Electrical and Electronics

A simple homemade Van de Graaff generator

2011-05-01T10:36:00.000-07:00

A simple homemade Van de Graaff generator

In the previous two projects, we stole high voltage from a television set to power our high voltage motors. In this project we will build a device that can generate 12,000 volts from an empty soda can and a rubber band.

The device is called a Van de Graaff generator. Science museums and research facilities have large versions that generate potentials in the hundreds of thousands of volts. Ours is more modest, but is still capable of drawing 1/2 inch sparks from the soda can to my finger. The spark is harmless, and similar to the jolt you get from a doorknob after scuffing your feet on the carpet.

To build the toy, you need:

An empty soda can
A small nail
A rubber band, 1/4 inch by 3 or 4 inches
A 5x20 millimeter GMA-Type electrical fuse (such as Radio Shack #270-1062)
A small DC motor (such as Radio Shack #273-223)
A battery clip (Radio Shack #270-324)
A battery holder (Radio Shack #270-382)
A styrofoam cup (a paper cup will also work)
A hot glue gun (or regular glue if you don't mind waiting)
Two 6 inch long stranded electrical wires (such as from an extension cord)
Two pieces of 3/4 inch PVC plumbing pipe, each about 2 or 3 inches long
One 3/4 inch PVC coupler
One 3/4 inch PVC T connector
Some electrical tape
A block of wood

That sounds like a lot of stuff, but take a look at the step-by-step photos below, and you will find that the whole project can easily be put together in an evening, once all the parts have been collected.

We'll start at the bottom, and work our way up.

Click on the image for a larger picture

The first thing to do is to cut a 2 to 3 inch long piece of 3/4 inch PVC pipe, and glue that to the wooden base. This piece will hold the generator up, and allow us to remove it to more easily replace the rubber band, or make adjustments.

The PVC "T" connector will hold the small motor. The motor fits too loosely by itself, so we wrap paper or tape around it to make a snug fit. The shaft of the motor can be left bare, but the generator will work a little better if it is made fatter by wrapping tape around it, or (better) putting a plastic rod with a hole in the center onto the shaft to act as a pulley for the rubber band.

Next, we drill a small hole in the side of the PVC "T" connector, just under the makeshift pulley on the motor. This hole will be used to hold the lower "brush", which is simply a bit of stranded wire frayed at the end, that is almost touching the rubber band on the pulley.

As the photo shows, the stranded wire is held in place with some electrical tape, or some other tape or glue.

The rubber band is now placed on the pulley, and allowed to hang out the top of the "T" connector.

Click on the image for a larger picture

Next, cut another 3 or 4 inch piece of 3/4 inch PVC plumbing pipe. This will go into the top of the "T" connector, with the rubber band going up through it. Use the small nail to hold the rubber band in place, as in the photo below. The length of the PVC pipe should be just enough to fit the rubber band. The rubber band should not be stretched too tightly, since the resulting friction would prevent the motor from turning properly, and increase wear on the parts.

Click on the image for a larger picture

Cut the styrofoam cup about an inch from the bottom, and carefully cut a 3/4 inch diameter hole in the center of the bottom of the cup. This hole should fit snugly onto the 3/4 inch PVC pipe.

Click on the image for a larger picture

Now drill three holes near the top of the PVC union coupling. Two of these holes need to be diametrically opposite one another, since they will hold the small nail which will act as an axle for the rubber band. The third hole is between the other two, and it will hold the top "brush", which, like the bottom brush, will almost touch the rubber band.

The top brush is taped to the PVC union coupler, and the coupler is placed on the 3/4 inch pipe, above the styrofoam cup collar. The rubber band is threaded through the coupler, and held in place with the small nail, as before.

Bare the top brush (so it has no insulation) and twist it to keep the individual wires from coming apart. You can solder the free end if you like, but it is not necessary.

The free end of the top brush will be curled up inside the empty soda can when we are done, and thus electrically connect the soda can to the top brush.

Click on the image for a larger picture

We need a small glass tube to act as both a low-friction top pulley, and as a "triboelectric" complement to the rubber band, to generate static electricity by rubbing. Glass is one of the best materials to rub against rubber to create electricity.

We get the tube by taking apart a small electrical fuse. The metal ends of the fuse come off easily if heated with a soldering iron or a match. The solder inside them drips out when they come off, so be careful. The glass, the metal cap, and the molten solder are all quite hot, and will blister the skin if you touch them before they cool.
Save the metal caps -- we will use them in a future project!

Click on the image for a larger picture

The resulting glass tube has nice straight, even edges, which are "fire polished" for you, so there is no sharp glass, and no uneven edges to catch on the PVC and break the glass.

The next step is a little tricky. The small nail is placed through one of the two holes in the PVC union coupler, and the small glass tube is placed on the nail. Then the rubber band is placed on the glass tube, and the nail is then placed in the second hole. The rubber band is on the glass tube, which is free to rotate around the nail.

Click on the image for a larger picture

Now we glue the styrofoam collar in place on the PVC pipe. I like to use a hot glue gun for this, since the glue can be laid on thickly to stabilize the collar, and it sets quickly and does not dissolve the styrofoam.

Click on the image for a larger picture

At this point we are ready for the empty soda can. Aluminum pop-top cans are good for high voltage because they have nice rounded edges, which minimizes "corona discharge".

With a sharp knife, carefully cut out the top of the soda can. Leave the nice crimped edge, and cut close to the side of the can so as to leave very little in the way of sharp edges. You can smooth the cut edge by "stirring" the can with a metal tool like a screwdriver, pressing outward as you stir, to flatten the sharp edge.

Tuck the free end of the top brush wire into the can, and invert the can over the top of the device, until it rests snugly on the styrofoam collar.

Click on the image for a larger picture

The last step is to attach the batteries. I like to solder a battery clip to the motor terminals, and then clip this onto either a nine-volt battery, or a battery holder for two AA size batteries. The nine-volt battery works, but it runs the motor too fast, making a lot of noise, and risking breakage of the glass tube. It does, however, make a slightly higher voltage, until the device breaks.

Click on the image for a larger picture

To use the Van de Graaff generator, simply clip the battery to the battery clip. If the brushes are very close to the ends of the rubber band, but not touching, you should be able to feel a spark from the soda can if you bring your finger close enough. It helps to hold onto the free end of the bottom brush with the other hand while doing this.

Click on the image for a larger picture

To use our generator to power the Franklin's Bells we built in the previous section of the book, clip the bottom brush wire to one "bell", and attach a wire to the top of the generator, connecting it to the other "bell".

The pop-top clapper of the Franklin's Bells should start jumping between the soda cans. It may need a little push to get started.

Click on the image for a larger picture

How does it do that?

You may have at one time rubbed a balloon on your hair, and then made the balloon stick to the wall. If you have never done this, try it!

The Van de Graaff generator uses this trick and two others to generate the high voltage needed to make a spark.

The first trick

When the balloon made contact with your hair, the molecules of the rubber touched the molecules of the hair. When they touched, the molecules of the rubber attract electrons from the molecules of the hair.

Then you take the balloon away from your hair, and some of those electrons stay with the balloon, giving it a negative charge.

The extra electrons on the balloon repel the electrons in the wall, pushing them back from the surface. The surface of the wall is left with a positive charge, since there are fewer electrons than when it was neutral.

The positive wall attracts the negative balloon with enough force to keep it stuck to the wall.

If you collected a bunch of different materials and touched them to one another, you could find out which ones were left negatively charged, and which were left positively charged.

You could then take these pairs of objects, and put them in order in a list, from the most positive to the most negative. Such a list is called aTriboelectric Series. The prefix Tribo- means "to rub".

The Triboelectric series

Most positive
(items at this end lose electrons)

asbestos
rabbit fur
glass
hair
nylon
wool
silk
paper
cotton
hard rubber
synthetic rubber
polyester
styrofoam
orlon
saran
polyurethane
polyethylene
polypropylene
polyvinyl chloride (PVC pipe)
teflon
silicone rubber
Most negative
(items at this end steal electrons)

Our Van de Graaff generator uses a glass tube and a rubber band. The rubber band steals electrons from the glass tube, leaving the glass positively charged, and the rubber band negatively charged.

The second trick

The triboelectric charging is the first trick. The second trick involves the wire brushes.

When a metal object is brought near a charged object, something quite interesting happens. The charged object causes the electrons in the metal to move. If the object is charged negatively, it pushes the electrons away. If it is charged positively, it pulls the electrons towards it.

Electrons are all negatively charged. Because like charges repel, and electrons are all the same charge, electrons will always try to get as far away from other electrons as possible.

If the metal object has a sharp point on it, the electrons on the point are pushed by all of the other electrons in the rest of the object. So on a point, there are a lot of electrons pushing from the metal, but no electrons pushing from the air.

If there are enough extra electrons on the metal, they can push some electrons off the point and into the air. The electrons land on the air molecules, making them negatively charged. The negatively charged air is repelled from the negatively charged metal, and a small wind of charged air blows away from the metal. This is called "corona discharge", because the dim light it gives off looks like a crown.

The same thing happens in reverse if the metal has too few electrons (if it is positively charged). At the point, all of the positive charges in the metal pull all the electrons from the point, leaving it very highly charged.

The air molecules that hit the metal point lose their electrons to the strong pull from the positive tip of the sharp point. The air molecules are now positive, and are repelled from the positive metal.

The third trick

There is one more trick the Van de Graaff generator uses. After we understand the third trick, we will put all of the tricks together to see how the generator works.

We said earlier that all electrons have the same charge, and so they all try to get as far from one another as possible. The third trick uses the soda can to take advantage of this feature of the electrons in an interesting way.

If we give the soda can a charge of electrons, they will all try to get as far away from one another as possible. This has the effect of making all the electrons crowd to the outside of the can. Any electron on the inside of the can will feel the push from all the other electrons, and will move. But the electrons on the outside feel the push from the can, but they do not feel any push from the air around the can, which is not charged.

This means that we can put electrons on the inside of the can, and they will be pulled away to the outside.

We can keep adding as many electrons as we like to the inside of the can, and they will always be pulled to the outside.

Putting all three tricks together

So now let's look at the Van de Graaff generator with our three tricks in mind.

The motor moves the rubber band around and around. The rubber band loops over the glass tube and steals the electrons from the glass.

The rubber band is much bigger than the glass tube. The electrons stolen from the glass are distributed across the whole rubber band.

The glass, on the other hand, is small. The negative charges that are spead out over the rubber band are weak, compared to the positive charges that are all concentrated on the little glass tube.

The strong positive charge on the glass attracts the electrons in the wire on the top brush. These electrons spray from the sharp points in the brush, and charge the air. The air is repelled from the wire, and attracted to the glass.

But the charged air can't get to the glass, because the rubber band is in the way. The charged air molecules hit the rubber, and transfer the electrons to it.

The rubber band travels down to the bottom brush. The electrons in the rubber push on the electrons in the wire of the bottom brush. The electrons are pushed out of the wire, and into whatever large object we have attached to the end of the wire, such as the earth, or a person.

The sharp points of the bottom brush are now positive, and they pull the electrons off of any air molecules that touch them. These positively charged air molecules are repelled by the positively charged wire, and attracted to the electrons on the rubber band. When they hit the rubber, they get their electrons back, and the rubber and the air both lose their charge.

The rubber band is now ready to go back up and steal more electrons from the glass tube.

The top brush is connected to the inside of the soda can. It is positively charged, and so attracts electrons from the can. The positive charges in the can move away from one another (they are the same charge, so they repel, just like electrons). The positive charges collect on the outside of the can, leaving the neutral atoms of the can on the inside, where they are always ready to donate more electrons.

The effect is to transfer electrons from the soda can into the ground, using the rubber band like a conveyor belt. It doesn't take very long for the soda can to lose so many electrons that it becomes 12,000 volts more positive than the ground.

When the can gets very positive, it eventually has enough charge to steal electrons from the air molecules that hit the can. This happens most at any sharp points on the can. If the can were a perfect sphere, it would be able to reach a higher voltage, since there would be no places where the charge was more concentrated than anywhere else.

If the sphere were larger, an even higher voltage could be reached before it started stealing electrons from the air, because a larger sphere is not as "sharp" as a smaller one.

The places on our soda can where the curves are the sharpest are where the charge accumulates the most, and where the electrons are stolen from the air.

Air ionizes in an electric field of about 25,000 volts per inch. Ionized air conducts electricity like a wire does. You can see the ionized air conducting electricity, because it gets so hot it emits light. It is what we call a spark.

Since our generator can draw sparks that are about a half inch long, we know we are generating about 12,500 volts.

Some fun with the Van de Graaf generator

One of the fun things to do with a Van de Graaff generator is to show how like charges repel.

We take a paper napkin, and cut thin strips of the lightweight paper. We then tape the ends of the paper together at one end, and tape that end onto the Van de Graaf generator.

The effect will look somewhat like long hair cascading down the soda can.

Now turn the Van de Graaff generator on. The thin strips of paper all get the same charge, and start to repel from one another. The effect is "hair raising". The strips start to stand out straight from the can, like the hair on the back of a scared cat.

Click on the image for an animated movie

A high voltage ion motor

This motor is very simple to build, and goes together in a few minutes. All you need is two pieces of wire, the small metal cap from the fuse we took apart in the previous project, and some cellophane tape.

The motor creates an ion wind that spins it around like a helicopter.

Click on the image for a larger picture

First, take one piece of wire (a straightened paper clip will do), and cut the end at an angle so it is sharp. Bend the other end into a rough loop or triangle, so the wire will stand up with the sharp point facing straight up. A little tape will help hold it onto the table, or a block of wood.

Click on the image for a larger picture

The armature (the part that spins) is made from the other piece of wire and the metal cap we saved when we took apart the fuse. Sharpen both ends of the wire by cutting the ends at a diagonal, like we did with the base wire. Bend the wire into an S shape. The pointed ends of the wire should point at 90 degrees from the center straight part of the wire.

Click on the image for a larger picture

Attach the metal cap to the center of the wire with tape. Place the cap onto the pointed end of the base wire, and bend the S shaped ends of the armature wire down, so it will balance easily on the sharp end of the base wire.

The armature should now spin freely if you tap it gently.

Connect a source of high voltage to the base wire using an alligator clip or a wire. The high voltage source can be the Van de Graaff generator, or just a couple square feet of aluminum foil pressed against the front of your television set, as we did in earlier projects.

As the high voltage is turned on, the armature will start to spin in the direction away from the sharp points. The Van de Graaff generator may need a good ground, or a person holding onto the ground wire. The television will give the motor a good kick every time it is turned on or off, and turning it on and off every second will get it spinning quite rapidly.

How does it do that?

The motor works by ionizing the air, and then pushing against the ionized air.

As we explained in the previous project, electric charges are concentrated by sharp points. The sharp points on the ends of the armature concentrate the charges so much that the air around the points becomes charged as well.

Since the air has the same charge as the wire, the two repel one another. You can actually feel a small wind coming from the sharp point. As the wire pushes on the charged air, they both move away from one another. The air blows away, and the wire spins.

proteus at 89c2051 Layout

2010-10-18T07:58:00.000-07:00

basic line follower robot..

2010-10-05T04:44:00.001-07:00

AT89C52 RF ID BASED SECURITY SYSTEM DOOR OPEN AND CLOZ..

2010-10-03T07:47:00.000-07:00

cell phone operated robot.........

2010-10-02T13:22:00.000-07:00

Microcontroller Based Automatic Railway Gate Control system...

2010-10-02T13:00:00.000-07:00

basic microcontroller interfacing circuits and programs

2010-10-02T12:47:00.000-07:00

lcd interfacing with 89c52..................

; ***********************************************
; * PRAVEEN LABS..... *
; * LCD INTERFACING *
; ***********************************************
ORG 0000H ; RESET ENTRY POINT
;;;;;;;;;;;; LCD PROG..... ;;;;;;;;;;;;;;;;;;;;;;
MAIN:
MOV A,#38H
ACALL COMMAND1
MOV A,#0EH
ACALL COMMAND1
MOV A,#06H
ACALL COMMAND1
MOV A,#0CH
ACALL COMMAND1
MOV A,#01H
ACALL COMMAND1

;;;;;;;;;; DISPLAY POINT ;;;;;;;;;;

ACALL DELAY
MOV A,#80H
ACALL COMMAND1
MOV DPTR,#DATA0
ACALL PASS_DATA1
ACALL DELAY

MOV A,#0C0H
ACALL COMMAND1
MOV DPTR,#DATA1
ACALL PASS_DATA1
ACALL DELAY
ACALL DELAY

SJMP MAIN

;;;;;;;;;;;;DISP COMMANDS ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
PASS_DATA1:

JUMP1: CLR A
MOVC A,@A+DPTR
ACALL DATA_D1
acall secdel
acall secdel
INC DPTR
CJNE A,#00H,JUMP1
RET
COMMAND1:
ACALL READY1
CLR P2.0
CLR P2.1
SETB P2.2
MOV P0,A
CLR P2.2
RET
DATA_D1:
ACALL READY1
SETB P2.0
CLR P2.1
SETB P2.2
MOV P0,A
CLR P2.2
RET
READY1:
SETB P0.7
CLR P2.0
SETB P2.1
HEX1: CLR P2.2
SETB P2.2
JB P0.7,HEX1
RET
;;;;;;;;;;;;;;; 1 BY 1 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

SECDEL:
MOV 75H,#0FFH
MOV 76H,#0FFH
HERE8:
DJNZ 75H,HERE8
DJNZ 76H,HERE8
RET
;;;;;;;;;;;;;;;;;;;;; DELAY ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
DELAY: MOV 70H,#0FFH
MOV 71H,#0FFH
MOV 72H,#02H
LOOP:
DJNZ 70H,LOOP
DJNZ 71H,LOOP
DJNZ 72H,LOOP
RET
;;;;;;;;;;;;;;; DISPLAY DATA ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
DATA0: db "PRAVEEN LABS....",00
DATA1: db " LCD INTERFACING",00

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
END

dtmf based home automation 6 devices control....

2010-10-02T12:29:00.000-07:00

coming soon....speed breaker electricity generation..

2010-10-02T06:01:00.000-07:00

mechanical designs..............................

running brake lights.. for bikes.....

2010-09-21T08:43:00.001-07:00

AT89C2051 based DANCING LEDS

2010-09-20T04:17:00.000-07:00

guest article by Barbara Young

2010-06-18T12:07:00.000-07:00

Here’s a simple option to learn how solar panels work

What is solar energy ?

Solar power is radiant energy which is produced by the sun. Daily the sun radiates, or sends out, an incredible quantity of energy. The sun radiates more energy in a second than people have used since the beginning of time!

The energy of the Sun originates from within the sun itself. Like other stars, the sun is really a big ball of gases––mostly hydrogen and helium atoms.

The hydrogen atoms in the sun’s core combine to create helium and generate energy in a process called nuclear fusion.

During nuclear fusion, the sun’s extremely high pressure and temperature cause hydrogen atoms to come apart and their nuclei (the central cores of the atoms) to fuse or combine. Four hydrogen nuclei fuse to become one helium atom. But the helium atom contains less mass compared to four hydrogen atoms that fused. Some matter is lost during nuclear fusion. The lost matter is emitted into space as radiant energy.

It takes an incredible number of years for the energy in the sun’s core to make its way to the solar surface, and then just a little over eight minutes to travel the 93 million miles to earth. The solar energy travels to the earth at a speed of 186,000 miles per second, the velocity of sunshine.

Simply a small portion of the energy radiated from the sun into space strikes the earth, one part in two billion. Yet this quantity of energy is enormous. Each day enough energy strikes the usa to supply the nation’s energy needs for one and a half years!

Where does all this energy go?

About 15 percent of the sun’s energy that hits the earth is reflected back to space. Another 30 percent is used to evaporate water, which, lifted in to the atmosphere, produces rainfall. Solar energy is absorbed by plants, the land, and the oceans. The rest could be employed to supply our energy needs.

Who invented solar technology ?

People have harnessed solar energy for years and years. Since the 7th century B.C., people used simple magnifying glasses to concentrate the light of the sun into beams so hot they would cause wood to catch fire. More than a century ago in France, a scientist used heat from a solar collector to make steam to drive a steam engine. At first of this century, scientists and engineers began researching ways to use solar technology in earnest. One important development was obviously a remarkably efficient solar boiler invented by Charles Greeley Abbott, a united states astrophysicist, in 1936.

The solar water heater gained popularity at this time in Florida, California, and the Southwest. The industry started in the early 1920s and was in full swing just before World War II. This growth lasted until the mid-1950s when low-cost propane took over as primary fuel for heating American homes.

The public and world governments remained largely indifferent to the possibilities of solar power before oil shortages of the1970s. Today, people use solar energy to heat buildings and water and to generate electricity.

How we use solar power today ?

Solar power is used in several different ways, of course. There's two very basic types of solar energy:

* Solar thermal energy collects the sun's warmth through one of two means: in water or in an anti-freeze (glycol) mixture.

* Solar photovoltaic energy converts the sun's radiation to usable electricity.

Here are the five most practical and popular ways that solar energy is used:

1. Small portable solar photovoltaic systems. We have seen these used everywhere, from calculators to solar garden products. Portable units may be used for everything from RV appliances while single panel systems are used for traffic signs and remote monitoring stations.

2. Solar pool heating. Running water in direct circulation systems via a solar collector is a very practical method to heat water for your pool or hot spa.

3. Thermal glycol energy to heat water. In this method (indirect circulation), glycol is heated by natural sunlight and the heat is then transferred to water in a hot water tank. Using this method of collecting the sun's energy is much more practical now than ever before. In areas as far north as Edmonton, Alberta, solar thermal to heat water is economically sound. It can pay for itself in 36 months or less.

4. Integrating solar photovoltaic energy into your home or business power. In many parts on the planet, solar photovoltaics is an economically feasible solution to supplement the power of your home. In Japan, photovoltaics are competitive with other types of power. In america, new incentive programs make this form of solar energy ever more viable in many states. A frequent and practical way of integrating solar energy into the power of your home or business is through the use of building integrated solar photovoltaics.

5. Large independent photovoltaic systems. For those who have enough sun power at your site, you could possibly go off grid. It's also possible to integrate or hybridize your solar energy system with wind power or other types of renewable power to stay 'off the grid.'

How can Photovoltaic panels work ?

Silicon is mounted beneath non-reflective glass to produce photovoltaic panels. These panels collect photons from the sun, converting them into DC electrical power. The power created then flows into an inverter. The inverter transforms the power into basic voltage and AC electricity.

Solar cells are prepared with particular materials called semiconductors like silicon, which is presently the most generally used. When light hits the Photovoltaic cell, a specific share of it is absorbed inside the semiconductor material. This means that the energy of the absorbed light is given to the semiconductor.

The energy unfastens the electrons, permitting them to run freely. Pv cells also have more than one electric fields that act to compel electrons unfastened by light absorption to flow in a specific direction. This flow of electrons is a current, and by introducing metal links on the top and bottom of the -Photovoltaic cell, the current can be drawn to use it externally.

What are the advantages and disadvantages of solar power ?

Solar Pro Arguments

- Heating our homes with oil or natural gas or using electricity from power plants running with fossil fuels is a reason behind climatic change and climate disruption. Solar power, on the contrary, is clean and environmentally-friendly.

- Solar hot-water heaters require little maintenance, and their initial investment may be recovered in just a relatively small amount of time.

- Solar hot-water heaters can work in nearly every climate, even just in very cold ones. You just have to choose the right system for your climate: drainback, thermosyphon, batch-ICS, etc.

- Maintenance costs of solar powered systems are minimal and the warranties large.

- Financial incentives (USA, Canada, European states…) can aid in eliminating the price of the initial investment in solar technologies. The U.S. government, for example, offers tax credits for solar systems certified by by the SRCC (Solar Rating and Certification Corporation), which amount to 30 percent of the investment (2009-2016 period).

Solar Cons Arguments

- The initial investment in Solar Hot water heaters or in Photovoltaic Electric Systems is higher than that required by conventional electric and gas heaters systems.

- The payback period of solar PV-electric systems is high, as well as those of solar space heating or solar cooling (only the solar domestic hot water heating payback is short or relatively short).

- Solar water heating do not support a direct combination with radiators (including baseboard ones).

- Some air conditioning (solar space heating and the solar cooling systems) are expensive, and rather untested technologies: solar air conditioning isn't, till now, a truly economical option.

- The efficiency of solar powered systems is rather determined by sunlight resources. It's in colder climates, where heating or electricity needs are higher, that the efficiency is smaller.

About the Author - Barbara Young writes on motorhome solar power in her personal hobby web log 12voltsolarpanels.net. Her efforts are related to helping people save energy using solar energy to eliminate CO2 emissions and energy dependency.

The Morph concept

2010-06-16T20:45:00.000-07:00

The Morph concept

WATCH ITS VIDEO HERE
http://www.youtube.com/watch?v=IX-gTobCJHs

Launched alongside The Museum of Modern Art “Design and The Elastic Mind” exhibition, the Morph concept device is a bridge between highly advanced tec

hnologies and their potential benefits to end-users. This device concept showcases some revolutionary leaps being explored by Nokia Research Center (NRC) in collaboration with the Cambridge Nanoscience Centre (United Kingdom) – nanoscale technologies that will potentially create a world of radically different devices that open up an entirely new spectrum of possibilities.Morph concept technologies might create fantastic opportunities for mobile devices:

Newly-enabled flexible and transparent materials blend more seamlessly with the way we live

Devices become self-cleaning and self-preserving

Transparent electronics offering an entirely new aesthetic dimension

Built-in solar absorption might charge a device, whilst batteries become smaller, longer lasting and faster to charge

Integrated sensors might allow us to learn more about the environment around us, empowering us to make better choices

In addition to the advances above, the integrated electronics shown in the Morph concept could cost less and include more functionality in a much smaller space, even as interfaces are simplified and usability is enhanced. All of these new capabilities will unleash new applications and services that will allow us to communicate and interact in unprecedented ways.

Flexible & Changing Design

Nanotechnology enables materials components that are flexible, stretchable, transparent and remarkably strong. Fibril proteins are woven into a three dimensional mesh that reinforces thin elastic structures. Using the same principle behind spider silk, this elasticity enables the device to literally change shapes and configure itself to adapt to the task at hand.A folded design would fit easily in a pocket and could lend itself ergonomically to being used as a traditional handset. An unfolded larger design could display more detailed information, and incorporate input devices such as keyboards and touch pads.Even integrated electronics, from interconnects to sensors, could share these flexible properties. Further, utilization of biodegradable materials might make production and recycling of devices easier and ecologically friendly.

Self-Cleaning

Nanotechnology also can be leveraged to create self-cleaning surfaces on mobile devices, ultimately reducing corrosion, wear and improving longevity. Nanostructured surfaces, such as “Nanoflowers” naturally repel water, dirt, and even fingerprints utilizing effects also seen in natural systems.

Advanced Power Sources

Nanotechnology holds out the possibility that the surface of a device will become a natural source of energy via a covering of “Nanograss” structures that harvest solar power. At the same time new high energy density storage materials allow batteries to become smaller and thinner, while also quicker to recharge and able to endure more charging cycles.

Sensing The Environment

Nanosensors would empower users to examine the environment around them in completely new ways, from analyzing air pollution, to gaining insight into bio-chemical traces and processes. New capabilities might be as complex as helping us monitor evolving conditions in the quality of our surroundings, or as simple as knowing if the fruit we are about to enjoy should be washed before we eat it. Our ability to tune into our environment in these ways can help us make key decisions that guide our daily actions and ultimately can enhance our health.

Press Material

Other resources

To learn more about the “Design and The Elastic Mind” exhibition at The Museum of Modern Art visit MoMA webpage

To learn more about the Cambridge Nanoscience Centre visithttp://www.nanoscience.cam.ac.uk/

Photonics: The key to life in the 21st century

2009-12-16T21:42:00.000-08:00

"The more you know about it, the more you can make it work for you"
Written by The Welsh Opto-electronics Forum
This article will give you a taste of the technology that now affects everyone’s life, and is becoming increasingly important in the 21^st century. The 19^th century is often seen as the golden age of steam, the 20^th century an incredible advancement in electronics; whilst the 21^st century is set to be age of photonics or light. This article will also give you an insight into careers that make use of this technology.
WHAT ARE PHOTONICS and OPTO-ELECTRONICS?
Photonics and Opto-electronics are often used interchangeably. However, photonics is concerned with thegeneration (e.g. lasers), control (e.g. optics) and the detection (e.g. photo-multipliers) of light. Opto-electronics is the innovative combination of optics and electronics hardware to produce an exciting new range of products. This technology is powerful because it enables many new technical systems to work effectively. It includes any combination of light or images that works with electronics and can be as simple as the red light emitting diode (LED) that shows you that the TV is on, or as complex as the Hubble telescope in space.
WORLD LEADERS
Wales has many companies working in this area and several of them are recognised as world leaders in the technology. The work can be exciting; to stay in this position the companies need to use state of the art technology in design, manufacturing and testing. Two examples where this can be found are in military systems and in space
Try this experiment: look out of the window, then look back at this text for long enough for your eyes to re-focus and the words to become clear, then look out of the window and refocus your eyes again. How long did this take? 1 second? 2 seconds? When a pilot is flying a fighter aircraft at the speed of sound he cannot spend this amount of time looking away from the target, so the information from the critical instruments is displayed on a special glass panel in front of him, imaged so that his eyes do not have to change focus to read it. To do this well needs very good optical design, high-precision manufacture and advanced technology in holography and optical coatings....and Wales leads the world in this technology, with two companies in North Wales supplying to UK, USA and other Air Forces
On TV you will have seen satellites in space with large solar panels attached. These convert the sunlight directly into electricity, and the material to make solar cells for some of these satellites is made in South Wales. Space is a harsh environment for these electronic materials, and if unprotected the electrical output would fade away in about 18 months - which would mean no satellite TV programmes. To prevent this, greater than 50% of the satellites put up by the western world have their solar cells protected by an extremely thin piece of special glass made in North Wales.
OPTO-ELECTRONICS IN THE HOME
Without realising it, you are using opto-electronics throughout the day; look around for these examples, and imagine how modern life would be without them
Displays. How many displays of numbers that glow red or green do you have in your house? They are to be found on the alarm clock, the TV and video recorder, the microwave cooker and some ovens. There are even more liquid crystal displays which look black on grey; you will find them on watches, calculators, telephones, portable radios, tape and CD players and office machines such as faxes and copiers. Most laptop computers have liquid crystal displays and those in colour include other optoelectronic technology as well. Large flat screen TVs that you can hang on the wall are now available, and the price will soon be down to prices a home can afford.
Communications. When you make a phone call outside your local area you are almost certain to be using an optical fibre link with a laser sending the message down the fibre, and a detector receiving it at the other end. About 70% of the UK trunk lines are now optical fibre, and the rate at which optical fibre is being installed world wide now exceeds Mach 1! Optical fibre can carry far more information than copper wire and is the best way to link computers, outside broadcast TV cameras, Banks, Stock Exchange dealing rooms, etc. Again, in North Wales we have world class companies who make the fibre, the cables, and the electronics and control systems to go with it.
Cameras. Camcorders and Digital still cameras depend on a high quality multi- component optical lens, often with zoom capability - which needs an advanced computer programme to design. The picture is imaged onto an electronic detector with a regular array of extremely small picture elements (pixels). There can be more than 1000 x 1000 of these on an area the size of your thumbnail.
Entertainment. To control your TV you use a controller that sends a coded infra-red beam to the set. This light is detected at the set and converted to the control information. Your CD player uses a laser diode which is imaged onto the surface of the disc by a tiny precision lens made of plastic. Did you see the images of the football players projected onto the Arc de Triomphe after the World Cup final?. This was done using optoelectronic devices - lasers where the beam is switched on and off to create the image as it scans back and forth.
Manufacturing. Lasers are being used more and more for cutting and welding as the beam covers a small area, and can be directed by computer exactly where it is required. Most clothes made in large quantity for High Street stores have been cut to shape using a laser. The gears in your family car have probably been welded to the shaft using a laser. Also, the symbols all over the dashboard that show you (in the dark) where the heater controls are located, have been produced using a different type of laser to remove the black overcoat from a coloured, light transmitting piece of plastic to reveal the symbols.
Energy. The effect of sunlight on various materials, generating a voltage and flow of electrons, give rise to enormous possibilities in generating electricity with no CO₂ production. The material most commonly used is silicon. Sharp the world leader in the manufacture of solar cells has its factory in North Wales, supplying 200MW for the European market! At the Technium OpTIC in North Wales the south facing part of the building is covered with 1000m² of photovoltaic cells (solar cells). This can achieve up to 95kW peak on good days of strong sunshine in summer. However, it will also work on dull days and during the winter months.
IS OPTO-ELECTRONICS HARD TO UNDERSTAND?
Yes and No! If you are a research worker developing a new blue laser for use in the next generation of computer discs, you will be using skills that require more than a University degree, but the great importance of opto-electronics is that it finds many applications in life where what it does is important, and it is not necessary for the user to appreciate completely how it does it. After all, you can make good use of a TV controller without knowing what optics or electronics are inside it, or being able to design one.
But it does help to have some knowledge of the basic concepts, as this will help you to get the best out of the equipment - if you know that light has to come out of the red window on the controller you won’t cover it with your finger.
There are several different types of lasers and they are critical to many optoelectronic applications. What is a laser and how does it differ from a light bulb? There are two main differences; the light from a bulb is produced continuously from a white hot wire; it contains light of all colours and is emitted in all directions. A laser emits light of one colour (or light frequency), in a controlled way in one direction only and because of this high intensities can be achieved. Light can be emitted continuously or in a short burst. The latter gives a high power output over that very short time.
One way of understanding this difference in the way light is emitted is to compare it to sound. Imagine the River Dance group was on a stage and walking around in any direction they liked. The sound would be approximately continuous (but not very loud) and all frequencies are present as there is no control of the time when their feet touch the floor - this is like the light bulb. When they dance in time together, the sound of each footstep is much louder, and the beats come at a regular frequency - this is like the laser. If they all jump in the air and come down at the same time the sound is loudest, and this is like the pulse of the laser. In the laser, special mirrors at each end ensure that all the light comes out in one direction only.
WHAT OPPORTUNITIES ARE THERE FOR CAREERS USING OPTO-ELECTRONICS?
Because it finds application in so many fields, careers that need an understanding of opto-electronics are numerous: doctors use lasers for surgery as do civil engineers for surveying; biochemists use the detection of light emission to monitor the effectiveness of anti-cancer drugs, and even supermarket managers rely on the everyday bar code scanner used for controlling their stock. In depth examples follow.
Knowledge and understanding of opto-electronics comes from studying subjects like Maths, Physics, Chemistry and of course, Technology; studying at GCSE level will introduce you to opto-electronics, and you could go into a lot of depth by choosing an opto-electronics theme for your major project in Technology. Beyond 16, choosing apprenticeships, traineeships, or ‘A’ Levels can all lead to careers with opto-electronics companies in North Wales and beyond. Many employees have studied at Degree level, and they are now influencing the technologies we use everyday, both now and in the future.
CAREERS INVOLVING OPTO-ELECTRONICS
Careers using opto-electronics are for people with a wide range of skills and knowledge at different levels, and include the manufacture of components, design, assembly and testing of systems, technical sales and fundamental research. Some examples of occupations and their use of opto-electronics are:-
Biological Researcher and Technician - uses microscopes with video camera attachment so that images of samples can be enhanced by computer to bring out information not normally visible. By chemically attaching firefly-like molecules to drugs, and by measuring the weak light emitted after treatment, it is possible to measure how effectively they target cancer cells using sensitive opto-electronics.
Civil Engineer - uses a laser beam with a theodelite to create a straight line over long distances to measure the angle of a proposed road bridge from a reference position.
Autofocus camera lens designer - is part of a team who use computer programmes to design the lens, the sensors and electronics to measure the sharpness of the image to control the focus, and CAD (Computer Aided Design) to design the components and housings. Such components may be made with machines which depend on optoelectronic equipment to achieve the required accuracy.
Heating Engineer - uses a Thermal Imaging camera to give a high quality picture showing the temperature distribution across a scene, which enables them to measure heat loss from a poorly insulated factory or the discharge of hot effluent into a river.
Communications System Installer - couples optical fibres to electronic systems to route the information between computers, monitors etc. or to control a production machine.
Conservation Specialist - uses laser beams to blast away the grime that has built up on buildings and statues with less damage than other abrasive techniques.
Environmental Inspector - uses a laser beam projected into the smoke plume from a factory to monitor the levels of the different gases emitted to see if they are within permitted limits.
Quality Control Inspector - uses apparatus which measures the precise colour spectrum of the food product so that e.g. bad beans can be automatically rejected . Sorting of produce of different sizes into bins can be done using the dimensions of the video image.
Surgeon - uses a slip-on device over the patients thumb which monitors an infra-red beam to continuously measure the pulse rate. Also, inserts a fibre optic endoscope into the patient with a camera attached, and when the defect has been located cuts it away with a laser beam which is transmitted down the fibre optic.
Skilled Machinist - uses various types of laser beam under computer control e.g. to cut holes finer than a human hair, treat or decorate the metal surface, or join components together in a vacuum where there is negligible contamination of the weld.

seminars

2009-09-09T04:04:00.000-07:00

hello every one ,

i found a good site for paper presentations plz go through this site if u need any seminar topics

http://techalone.com/index.php/category/electrical-seminar-topics/

Some UnderGraduate Project Ideas

2009-05-24T00:57:00.000-07:00

Here are some undergraduate ( B.Tech 4th year) project ideas that are related to robotics and A.I which you can do to increase you experience and exposure in the field. Remember these projects are not quick fix projects generally carried out ( VB ,Oracle, ASP crap , or some simple copying of EFY circuit ) these will require lots of work and research from your side, sometimes loads of money too.

If you need any help regarding these please go to http://www.roboticsindia.com/

AUTOMATED MISSILE GUIDANCE SYSTEM {Aeronautics/EC} : The idea is a blend of
aeronautics(amateur),mechanics,mathematics,A.I.,electronics and communication(embedded systems) and of course some real innovative minds.but im sure u gonna blow'em up.No this is'nt a joke.These kinda projects have been done before by undergraduates from different universties.The project needs a fine understanding of mechanics and some state of art virtual processors like MATLAB (the one and only).this one needs real talent.

3-D PAINTER {EC , CS} : First of all this project is a state of art combination of graphics programming and embedded system designs. Its kinda fun making this project.. Actually it works like this -> you move an electronic pen or a small electronic stylus attached to your finger in the AIR and the computer will decode the motion of the stylus(attached to the computer with an embedded system) and convert it into a real time design. Yes this project will be a real time system.Ofcourse the stylus will be having accelerometers.

Autonomous Chess/Checkers Robot [CS/ME/EE]: This project is a big project and will involve expertise in many fields like micro controllers, A.I, kinematics, image processing, speech processing and recognition. This project will involve building a robot arm, which will pick and place the pieces on the board. The board recognition will be provided by web cam and the arm will be controlled by servos (SSC). Voice recognition and Synthesis will be used to interact with the user. You can use chess/checkers module or write your own (min-max).

Autonomous De-mining Vehicle [CS/EE]: This project though not very big is quite interesting. A Big Study WMR will have to be built, equipped with GPS and other navigational aids it will be able to map an area and detect metal objects and other irregularities in the terrain using metal detectors and web cam. Either is can drop a marker to mark the position of mine or simulate de-mining (place a small charge above the mine and detonating it from a safe distance]. All this data will also build a map of the area, which is available remotely.

Legged Robots [ME/EE]: These projects mainly involve lots of Mechanical design and some basic Electronics to control the robot. You can also put in some sensors and some basic object avoidance. If you want to go ahead make the robot a little advanced make it learn how to walk and put in some kind of behavior.

Home Robot [CS/EE]: This robot will be quite interesting and you might even keep it at your home once its done. The aim is to build a personal robot equipped with video/audio/speech which will be able to carry out basic tasks like switching off kitchen lights when your in the bedroom, by going to the kitchen and then using IR, switching channels on TV. Talk back to you using some basic NLI. The robot will be a WMR with ability to map its environment and successfully navigate it. All the processing will be done offline using a PC. The camera will be a Wireless blue tooth camera. And you can also use a High bandwidth RF data link to the PC. If you want to save or RF and Wireless cams (they are EXPENSIVE) you can go in for a ITX based embedded system board.

Balancing Robot [CS/EE]: Though not a very complicated robot this is a iteresting one.You have to build a robot which balances itself and can manover around on two wheels only. The balnce is provided using a combination of Gyroscope and Accelometer. One the balance is achived slight bend towards a direction will make your robot move in that one.REquire more prgramming than electronics / Mech also makes for a interesting project.Search the net as people have built many balacing bots. THere are also ones which balance inverted pendulums etc.

Roomba clone [CS/EE/ME]: Try and clone the functionality of Roomba in our own version of a robot. This robot is usefull as well as cool. Insted of a vaccum u can use a sweeper mechanism like swivel sweeper ( Goole to search for it ). You can put quite some inteligence in your tiny robot if you want to like aumated map building, path finding and other such cool learning features( Depending on the time you have ) . Have fun project is not very exp yet is quite fun and usefull after the thing has been achived.

Autonomous Surveillance robot:These ahve been commen today.We hear of some students doing bots that can track down a person who is struck up inside the debris of a collapsed building or one that can see(actually sense) if a soldier is severely wounded so that he cannot move and carry him to a safer place.Such bots need a high degree of automation and sensing.

plz read according to the numbers given in the titles

2009-05-18T10:48:00.000-07:00

I am sorry for the order of posts in embedded electronics...!

kindly read the topics in embedded electronics according to the page numbers given in the title of the posts

Beginning Embedded Electronics - 11

2009-05-15T04:01:00.000-07:00

Common Mistakes, Tips and Tricks

All grounds need to be connected together.
TX/RX loop back trick: When in doubt of a serial conversion circuit, short the TX and RX pins together to get an echo.
Normal length wires for breadboard connections: Don't use a 9" wire where a 2" wire will do.
Minimize short potential in your breadboard wiring: Don't expose an inch of wire from the insulation if all you need is 1/4".
You will learn best when you have a *simple* project to work on. Don't create the 'house-pet robot' just yet.
Google is, of course, your friend. When you don't know, go do some research.
for(x = 0 ; x <>
Soldering basics: Wet your @#$% sponge.
Take your time with ground plane solder joints. Do not be fooled by a cold joint.
Never trick yourself into thinking you're that good. Print out a 1:1 and compare the footprints!
Check that TX and RX are wired correctly to all peripherals. TX/RX swap is the one of the greatest causes of PCB failures.
When laying out a PCB with SMD micros, don't forget to include the programming port!
Don't run silkscreen across pads.
Connector PCB footprint mis-numbering: always check the pin number on your connector - they can have very obfuscated schemes.
In Eagle, use vector fonts only!
Review your gerber files before submitting them.

Beginning Embedded Electronics - 10

2009-05-15T03:55:00.000-07:00

Lecture 10 - Eagle: Creating a new part

You can dig around the Eagle libraries all you want. Very quickly you will discover that you need to create a new part. This can be very daunting at first. The following tutorial breaks down how we create a new part in Eagle. There are some recommendations here that are good to follow, but we are by no means experts at Eagle. This is going to be very long and painful, just try to get through it. These basics will hopefully form the foundation of all your future project layouts.

You are welcome to use stock Eagle libraries but use them under extreme caution. I rarely use other people's libraries. Trusting someone else' part or footprint can be a sure fire way to render a pile of PCBs worthless. I've done this far too many times! It takes lots of failures to get good at creating decent schematic parts and solderable footprints. You will mess up, but you have to mess up before you can be good at it.

To get 5V out of a 1.5V battery, we use something called a DC to DC step-up converter. This handy part is not in the stock Eagle library so let's create a new part for this controller IC - the NCP1400 (datasheet).

The NCP1400 is a neat little step-up IC - we input a low voltage and get 5V out!

To start your first parts library:

Once the Library Editor is open, hit the Save icon and save your library with your name on it:

Click on create a new symbol. Name it 'NCP1400':

Create a red box by clicking on the 'Wire' button:

Don't worry about centering the box at this time.

Key commands to try out:

Scroll the scroll wheel on the mouse to zoom in/out
Click the scroll wheel (on the main work area) and hold shift to move the work area around
If the work area image looks corrupt, just zoom in/out to refresh the area

Add 5 pins to the box:

Press F4 and click on a pin. Name them according to the datasheet.

Pins are named, but we need to clean up how this part is sized and where the center is at. To grab the group press Alt+F7, click and hold, and drag from one corner of the work area to the opposite corner - boxing in the pins and part:

Once you have everything selected (everything should be highlighted red), press F7 and right click to move the group over the center cross. In my example part, I the right side was one block too far over so I sucked in the right side one square.

The image above shows the part centered and symmetrical.

NEVER change the grid size in the library editor or in the schematic layout editor. Leave it on 0.1inch steps and don't use the alternate 0.01 step. If you do, you won't be able to hook wires to the pin tie points.

Name and Value tags are always nice. Click on the text button and type '>NAME' and '>VALUE'. (Ok I lied. It's okay to use the alternate step size when moving around non-critical items like text. Hold the Alt key down while your placing the Name and Value tags to get them where you want them):

Once you have Name and Value placed, you'll notice that these are red when they are normally gray in color. Be sure to modify what layer these two strings are on. We need to change the >NAME tag to the Name layer, and >VALUE tag to the value layer. To do this:

Click on the wrench, then Layer.. Choose the layer you'd like to change the object to

Here is the final schematic part, centered and happy. If you want, you can change the pin definitions to indicate which pins are inputs, outputs, pwr, etc. I find these settings useful in a handful of situations. This is a simple enough part, we'll skip it.

Now for the footprint. Remember, when in doubt create your own footprint. Trusting anyone else' footprint without scrutinizing it closely is a very bad idea. If you're lucky, your datasheet will include a recommended footprint for the part you are working with. If it does not, google for the words 'recommended land pattern SOT-23' or whatever package you are looking for. The words 'land pattern' is the key.

Lucky us! The NCP1400 datasheet has a recommend footprint:

This takes some getting used to. There are two numbers from every dimension, and not all the dimensions are indicated?! Lower left corner shows mm/inches meaning the top number is the dimension in mm and the bottom number is that same dimension in inches. Sorry folks, it's a metric world. More and more devices are spec'd in mm only (connectors, ICs, etc). From the Library editor, click on Package and let's start creating the footprint for this device. This is actually a pretty common package type called SOT23-5, so let's use that name:

Throw down 5 pads:

Hmm, some of the layers are not showing - let's turn them all on:

Click 'All' and then 'Ok'. You should now be able to view the solder mask (in Eagle as the 'Top Stop' layer) and solder paste layers (aka 'Top Cream' layer).

Now back in your datasheet you will find the width of each pad to be 0.7mm and the height to be 1.0mm. Before we can go editing the pads, we need to put Eagle into metric mode. Press Alt+F10 and you should see the coordinates in the upper task bar switch to mm. To alter the size of the five pads to 0.7x1.0mm, click on the wrench, then Smd, then '...':

You will then be prompted to enter the X and Y dimensions in mm with an 'x' in between:

Remember the X dimension always comes first.

Now click on all 5 pads. All 5 pads should now be the correct size. I really prefer to center the footprint with the center of the work area. This means we need to work out the various dimensions:

Let's start with the easy pad - pin #2 will be located at (0,1.2). Before we can start moving pads, we need to adjust the alternate grid so that we can get the the side pads to 0.95mm. Click on the points/grid box:

Change the Alt: box from 0.1 to 0.05 and click on ok. Now lets move pin 2. In the work area, press F7, then hold control and click on a pad:

F7 issues the move command. Holding control while clicking on a pad causes the pad to try to center to the cursor (this way you know that the coordinates displayed in the upper left task bar are displaying where the very center of the pad is at and not where your cursor may have been off when you first clicked on the pad). Because the pads are locked onto the 1mm grid, you'll notice the pad jump from 3mm to 4mm, etc. While holding control, hold alt as well. The pad should now jump on the alternate grid of 0.05mm instead of 1mm. Important buttons to know:

Again, the scroll wheel will zoom in/out
Clicking the scroll wheel will drag the work area around
Holding the shift key will allow you drag the work area further

To position this pad to (0,1.2) I literally had to:

Hold Control and click on the pad
Hold Alt, Shift, and control with one hand
Scroll in with the scroll wheel
Click+drag the scroll wheel to get the work area centered
Release Shift
Move the cursor to position (0,1.2) (Remember to hold alt!)

This sounds really scary but after creating two footprints, you'll have it down without thinking about it.

Nifty

Press F4 and click on each pad renaming them to match the datasheet numbering:

Did you number them wrong? Double check. Make sure you get it right! We need to add a dimensional layer to indicate the size of the device. This is different than a silkscreen indicator. I like to use layer 51 (named 'tDocu' meaning top document layer?). This layer will only be displayed while we're playing on the layout window and won't show up on any production files. This allows us to display the physical size of awkward parts, hopefully avoiding collisions between bulky parts when we go to populate the PCB.

Why should be even care about these layers?

Here is our NCP1400 (label U4) next to three capacitors. See how crazy board layout can get? Notice C1 is next to U4 but the distance between them looks ok? When we add in the tDocu layer:

Whoa! That cap is way too close to the body of the NCP1400. You might be able to get those two components soldered onto the board, but it would be a mash up job. We need to know the rough physical outline of components during layout. To do that, we need to add a frame to our footprint.

Before we add lines to our footprint to indicate the physical size of our part, let's change the layer color - gray is a horrible color to try to see! Click on the 'Display' button, scroll down to layer 51 and double click on the gray box next to 'tDocu':

Then click on the gray 'Color' box and change it to something interesting like lemon yellow, then click ok. Anything you do on this layer will now be yellow.

Click on the 'Wire' button. Select layer 51 (this layer will be yellow in the drop down box the next time you close/open the Library editor).

You should now be able to lay down yellow lines. Put four of them down in a box:

Press escape to stop drawing. Now we need to move the edges of the box to the outside edge of our part. Checking the datasheet again:

Ahh manufacturing tolerances. They can't really tell us how big the B and A dimensions will be, so I always pick a value in the middle of the min/max. A = 3mm, B = 1.5mm. Remember we have to center the frame so the upper right corner of the frame will be at (1.5, 0.75).

Now go back to the footprint, press F7 to issue the move command. Hold the control key and click on the upper right corner of the frame. When you do this, the 1 pad may light up - this is because Eagle does not know which part you are trying to move - the pad or the line? If you left click, Eagle will begin moving the 1 pad because it is highlighted. Right click and the frame should highlight. Now left click and you should be moving the upper right corner of the frame. I know, its really confusing at first. It's actually really handy once you're used to it!

Once you've got the corner at (1.5,0.75), left click to anchor the corner at that location and adjust the other three corners.

I can almost see it now! Notice how the part extends past the edges of the pads? If we would have put a component (like an 0603 resistor) next to pads 3 and 4 the two component may have been bumping into each other. Electrically, the layout would have been fine but when we would go to populate the PCB, this regulator might have been right up against the neighboring part.

Finally, I highly encourage you to add a bit of silkscreen to this part. What does a board look like without silkscreen?

Can you tell where the components go and how they are supposed to get oriented without a silk indicator? I can't.

Add a little silkscreen and it's suddenly very apparent where the NCP1400 is supposed to go.

When you get a PCB with nothing but silver pads, the 4/5 pads on this part look a lot like the spot for an 0805 capacitor! Select layer 21 tPlace. You may notice this layer is gray as well! I hate gray. Re-color this layer to white. When you get your PCBs, the silkscreen is white, right? Might as well make them agree.

I zoomed way in, held alt to get onto the alternate grid, and ran the line from (-0.25, -0.75) to (0.25, -0.75). You really do not want to put silkscreen across your pads. This will negatively affect how the pads react to solder. It would foul a board or anything, it's just best to keep the silkscreen layer away from pads. You could butt the white line right up against the pad, but the silkscreen layers has the worst tolerances and the greatest skew. The white lines in your beautiful layout could end up a couple mm to the left or right when you get your PCBs from the fab house. Besides, 0.25 is such a nice start/finish number!

Create silkscreen lines for the sides as well. Don't worry about itty-bitty silkscreen lines inbetween the upper pads or the little corners. Very small silkscreen lines will either be ignored by the fab house or else they will just flake off.

When we laid out the tDocu layer, the wire thickness was 0.127mm or 0.005". 0.005" is also pronounced as '5 mil'. Time and time again, you will hear that fab houses can handle 8 mil traces and 8 mil spacing for their basic service (aka their cheap service). This means that no trace can be less than 0.008" in thickness and two traces cannot be closer than 0.008" to each other. Well guess what thickness our silkscreen traces are? The 5mil tDocu lines don't matter because they will not be printed or fabbed, but the 5mil silkscreen traces may give some fab houses fits! The fab house may increase the line thickness to 8mil, they may try to print the 5mil line as is and have it come out very thin with no weight, or they may not print it at all! Let's alter the thickness of the silkscreen lines to 8mil so that we are kosher with any fab house.

We're switching back to Imperial units! Press F10. Next click on the wrench, width, and '...':

Why doesn't Eagle have 8mil listed? I have no idea. Enter 0.008 into the box prompt. Click on the three silkscreen lines:

It looks a bit odd, but once you see it on a PCB, it will look great! The last things we need to do (I promise!) is to add a >NAME and >VALUE tag. Review the schematic component section to see how to do this in detail. Add two strings ('>NAME' and '>VALUE') and then modify the layers for these two strings to tName and tValue respectively.

And we're done with the footprint creation for this one part! Now you see why engineers and companies hoard their libraries. The first couple footprints you create will be totally botched and will probably kill your PCB layout. But once you get a part created, and you use it once or twice successfully, the part will be proven and you'll never have to worry about it again! With a collection of 20-30 known good parts, you'll be able to whip up very reliable PCBs in surprisingly little time.

To finish this part in our library, we need to relate the pin numbers on our footprint to the pin identifiers on our schematic part. Save your library and click on the Device button:

Name the new device NCP1400 and then click on the Add button:

Drop the schematic part in the center of the work area. Hit escape twice to get rid of the part window. Now click on the 'New' button in the Package area:

Double click on the SOT23-5 listing.

Notice the yellow exclamation point in the Package area? This means that a footprint is associated with the schematic part but the pins have not yet been assigned. Double click on the 'SOT23-5' text in the Package area:

Review page 1 of the NCP1400 datasheet to know what pins connect to what pad numbers:

Double clicking on a given name on one side will assign it to the highlighted choice on the opposite side. You've done a great job up to this point! Double check that your pad assignments are correct!

Right click on the Package name and click on Rename. Various different footprints can be associated with any given schematic part. To differentiate between parts, you can give the pin assignments different names. I mis-use this function a bit. I often name variants 'SMD', 'A', 'B', '8', '10', or in this case 'NCP1400'. Pick your poison.

It's ok if you do not give this device a variant name, but if you leave the default variant name as " and then try to add a new pad assignment you will get the "Package variant " already defined!" error:

Just rename one of the variants to a different name so that Eagle can add this new variant with the default " name.

Now let's add this newly created part to our schematic. Close the library editor and go back to the Eagle Control Panel. Click on File->New->Project. Name this new project - in this example we'll do 'Simon'. Right click on the Simon project and create a new Schematic:

The schematic editor should open. Now go back to the Eagle Control Panel and open your new Library:

You should see the NCP1400 part and the SOT23-5 footprint. Highlight the NCP1400 part and in the right screen click on ADD. The schematic editor will pop up allowing you to place the NCP1400.

And that's it! You now know how to create a component from scratch. Be sure to do a 1 to 1 print of your layout before sending it to the PCB fab house to verify all the parts against their respective footprints.

Beginning Embedded Electronics - 9

2009-05-15T03:53:00.000-07:00

Lecture 9 - Eagle: PCB Layout

To learn how to use Eagle, we are going to create a simple breakout board for a popular USB IC. The FT232RL is a USB to TTL serial converter. This section covers the physical layout of the PCB.

We've got the schematic captured and the connections should be made correctly. The next step is to arrange various components on a board and then send the board files out to a manufacturer (also called a fabrication or 'fab' house).

Layout is an art and engineers make bad artists. It's all about the small polishing - text labels, stand off holes, correct footprints. Just keep turning out PCBs and you'll see your layouts improve dramatically with practice.

Before you do anything, turn on vector fonts! If you don't, your silkscreen text will be off on every PCB you create:

From the Eagle control panel, click Options->User Interface

Select 'Always vector font'.

Above is a breakdown of all the different buttons in the Layout window. You can view the name of each button by hovering over the button with your mouse. Many of the short-cuts from the Schematic window still apply:

Press escape at any time to stop the current action and return to the Layout window
F7 to move a part
Alt+F7 to group a bunch together
F3 to delete a part
F4 to rename a part (change C7 to C2)
F5 to re-value a part (change 0.1uF to 10uF, etc)
F6 to smash a part (be able to move the name and value tags)
F9 to start routing a wire
Alt+F9 to rip up a wire

If you get this error while moving bits around:

This just means that you are trying to put a component outside of the allowed area. With the Light edition of Eagle, you can only place components in quadrant I (upper right quadrant), whereas the components show up by default in quadrant II (upper left quadrant). Just move the parts to a positive X and Y coordinate and you should be ok.

Starting with our current layout:

The first thing to do is correct the board outline. I don't know why Eagle slightly offsets the default border.

Make sure you're on a 0.1" grid by pressing F10. Then hit F7 and hold control while clicking near the origin. This will grab the frame corner and force it onto the 0.1" grid. Make the bottom left corner sit at (0,0):

Do this for the other three corners bringing them in to make a 1.5x1.0" square board size.

Now go to town bringing the components into the board area. Keep in mind the gold color un-routed 'air' wires. The less twisted you make these by creatively arranging your components, the easier the trace routing will be.

Remember:

Press F7 to move a component
Right click to rotate
Hold control to grab a component at its origin
Scroll wheel to zoom in/out

Hit the Ratsnest button from time to time to recalculate the air wires.

Here are the components arranged in a basic configuration. Another beef I have with Eagle is the default colors for the various layers make it impossible to see what is going to be printed on the silkscreen layer. Let's change the 'tPlace' layer to pure white and change the 'tDocu' layer to lemon yellow.

Click on the 'Display' button, scroll down to layer 51 and double click on the gray box next to 'tDocu':

Then click on the gray 'Color' box and change it to something interesting like lemon yellow, then click ok. Anything you do on this layer will now be yellow. Do the same for layer 21 'tPlace'.

Now this is starting to make sense! Anything in yellow is just there to indicate physical size. The yellow part of the USB connector is only there to indicate that the connector sticks over the edge that far. Only the white part of the USB connector footprint will actually show up on the silkscreen print on our PCB. Anything in light gray (tNames and tValues layers) will not print on the silkscreen layer. They're just there for your own reference. We can of course change how the various layers are processed (and include the value and name layers on the silkscreen) but this can cause a lot of squeezing and hassle. It's up to you and your design but we will leave the part indicators and values out of this layout.

The next thing we need to do, for all PCB layouts, is to add stand-off holes. These holes will allow you to insert a simple screw and hold a stand-off in place. Without standoffs, PCBs will sit uneven against a flat surface (because of the bumpy solder joints protruding on the bottom of the board). Having a PCB sit flat against a surface is also a bad idea electrically - I've sent $200 up in smoke because some bits of clipped wire shorted against the bottom of my board when I was troubleshooting it.

I like to use 4-40 screws and 0.25" diameter plastic standoffs on everything. These 4-40 screws need a 0.13" diameter hole and the standoffs have a 0.25" outside diameter that we will need to take into account. If you have not already done so, add four of the 'Stand-Off' components to the schematic (and therefore PCB). This component was created to couple the 0.13" drill with a keepout ring. This keepout ring helps show were the screw head will fall. If you fail to take this keepout layer into account, the screw will go through the hole, but the screw head may run into or short components.

Throw four standoff holes around the corners of your board.

Ahah! Now I see why I made that keepout circle. You can see where the standoffs would have run into the USB connector. Looks like we've got some bumping to do...

By using the group (Alt+F7) and the move (F7) commands, I increased the border to 1.5x1.2" which is a bit bigger than I would like, but for the purposes of this tutorial, we're not going to stress tight packing of components - rather we want to stress the basics for a good PCB. Notice how I flipped and dropped C3 and C4 down a bit? Time to add labels!

A 'C2' label is handy when you're populating a board or when you're troubleshooting a complex circuit, but on a day to day basis, you probably won't need to know where C2 is. On the other hand, the TX and RX pins will probably be used every time you use the board! You really should label anything that will be connected to the outside world. To add a text label to a pin, click on the 'Text' button:

A window will pop up asking you what text you would like to add. Type 'TX' and press enter. You will notice that the text may be appearing on an odd layer. Be sure that you add text on the tPlace layer.

Drop down the layer menu and select tPlace for top silkscreen text

Once you've placed 'TX', press escape. Eagle will now show the text window again. Enter 'RX' and press enter. Repeat for RX, VCC, and GND. When done, press escape twice to return to the layout window.

In this case we have VCC/GND/TX/RX to label:

Make sure you add your labels to the 'tPlace' layer!

To check which pin is connected to which net, hit the eye button and click on a pin.

Checkout the text at the bottom of the Eagle window - pin 1 is VCC. Do this for all the pins and arrange the labels accordingly. You should also take the font size down to 0.05:

To change the font size, click on the Wrench ('Change' button), select 'Size', then 0.05. Now click on each text that you want to change the size on.

Labels in place and lined up

Try to get all the labels with the same vertical and horizontal alignment. This is a nit picky aesthetic thing, but it shows on the final board.

You will have many board revisions. It's always good to add a date code to the board so that you can match your files to the board version in hand. Add text to the bottom copper layer to an inconspicuous spot. The easiest way to do this is to add text to the top copper layer then hit the mirror button (you can also hit the scroll wheel on the mouse to move the component to a different layer). This will automatically mirror the text and drop it to the bottom layer.

6-3-07 mirrored, on the bottom copper layer, and underneath the USB connector. There shouldn't be any signal traces in this part of the board so we're not wasting space. You could add text to the bottom silkscreen layer but some fab houses don't allow bottom silkscreen (it adds an extra printing step).

Also add some text to the top silkscreen layer indicating what the board is, what it does, who made it, etc.

Above is the completed board ready for trace routing.

Many people swear up and down that an auto-router is a bad idea. It may be, but if we're not concerned about trace impedance or high speed signals, an auto-router is a great way to whip up protos. Spend your time innovating, not routing mundane traces.

To auto-route the board, click on the 'Auto' button. The defaults are all fine except for the 50mil grid:

Change the Routing Grid to 8 (our fab house uses 8 mil traces and spaces).

Demo board auto-routed. Eagle files / PDF

It's not immaculate, but it will work just fine and the router took under 2 seconds to route. It would probably take me 5-10 minutes by hand. I will hand route sensitive parts of certain boards, but this is a very simple proto.

Things to check on every layout:

Date code
Silkscreen title and pin labels
Standoff holes
All connections routed
TX and RX routed correctly
Print off 1:1 and check footprints

Routing TX and RX correctly? What does this mean? I can't tell you how many times I've heard newbies say 'well my PCB would have worked, but the manufacturer swapped the TX and RX pins'. No, the manufacturer did not swap them, the newbie neglected to actually read the datasheet (RTFD!). Sometimes an RX pin is an input. Sometimes an RX pin is an output. If you get it wrong, you'll look like a dunce. Read the datasheet and verify that everything is kosher. In the case of our FT232RL breakout, the TX pin is an output and RX pin is an input (pretty standard). I'm going to change the silkscreen indicators to read 'RX-I' and 'TX-O'. This should remove any doubt in my mind when I'm using the board a year from now - and so I don't have to go digging up the datasheet.

The last thing to check - print off 1:1 means to print on paper and 1 to 1 scale of the board layout. Then place the components on top the paper to verify that everything fits their associated footprint.

Another quick note about printing layouts - this can be a great way to create an assembly sheet. While you've got the PCB editor open, press Alt+F11. This will turn off all the layers that are not pertinent to assembly. Print this, I normally scale it up 3 times, and hand write in what parts go where. Quick and effective way to create a cheat sheet for PCB population. Pressing F11 will bring back the normal layers but you may want to activate/deactivate a few others.

Now that we've got the board laid out, stand-off holes in place, date code in place, and accurate pin labels, it's time to mash up the layers and create some gerber files.

What's a gerber?

There are lots of different layout packages out there (Protel, Orcad, Eagle, PCB, etc). One way or another all the PCB fab houses out there need a way to control their machines to work with your layout files. The universal format is something called Gerber Files. Basically these are txt files with coordinates that tell the PCB machines to go to location X,Y and do something (drill, expose, etch, print, etc). Because there are different layers to your PCB, you need to create different text files for the different layers. This is where the Eagle CAM program comes into play.

Once you're good and happy with your PCB layout (there is no turning back after you submit the files!), click on the CAM button to bring up the processor. This window will allow you to do different things to different layers. Eagle comes with a couple default *.cam files. The most common ones are the gerb274x.cam and excellon.cam. I got tired of running two seperate processors. I am also a hold over from Protel and a different naming convention so I created my own single file CAM processor. You can snag it here. The sfe-gerb274x.cam is based on the default Eagle file with a few tweaks:

Layers are renamed for easier reading - top copper, bottom silkscreen, etc.
All the mirroring is turned off - this will make gerber inspection much easier
A top paste layer was added in case you want to create a solder paste stencil
Excellon drill file is created along with the 6 magic layers
Drill file is 2:4 Leading (remember this!)

What are these magical layers you ask of? Anytime you transmit a PCB layout to a gab house, you need to pass them 7 files, and 7 files only:

Top Copper (GTL)
Top Soldermask (GTS)
Top Silkscreen (GTO)
Bottom Copper (GBL)
Bottom Soldermask (GBS)
Bottom Silkscreen (GBO)
Drill File (2:4 leading - remember this)

What is this GTL, GTS? These are the file extensions that the CAM processor will produce. A silkscreen is also called an 'overlay' (hence, GTO). And for your reference, a soldermask is also called a solder 'stop layer' because the soldermask prevents solder from being where it is not wanted.

Some fab houses will charge extra for a bottom silkscreen layer. You can just ignore this layer if you need to. You will also see a GTP file extension. This is the Gerber Top Paste file. You can use this file to get a solder paste stencil cut it you want. One would think that a GTP file would be the same as the GTS (top soldermask file). But no!

On the left, the soldermask layer. On the right, the top paste layer. The soldermask layer exposes the pads and the vias. You wouldn't want solder paste in vias! So the paste layer only has the SMD component pads exposed.

To create these layers, click on File->Open->Job

And select the sfe-gerb274x.cam file. Then click 'Process Job'. Some status bars will blink by, and within a few seconds, you should have a handful of extra files in your project directory:

The magic 7 gerber files

Something I highly recommend is to review the gerber files before submitting them for fabrication. Viewing just what is going to the fab house can exposed potential problems that were shrouded before by all the extra layers and graphics in the Eagle layout window. There are some free viewers out there that will let you view the gerber layers together. Most of the free viewers require you to enter an email, require 15 seconds for them to advertise at you, limited to one layer, or other really annoying limitations. Luckily, Viewplot still exists. This free program will let you open and look at your layers easily and you don't have to fill out any silly forms to get to the download link! Be sure to select the drill file type '2:4 Leading' to matchup the holes to the layers.

Simple

But oh wait, what is that?

Silkscreen on top of a via

This silkscreen being broken up by the via is not a big deal. Mostly this is just to show how difficult it can be to detect problems from within the layout program. By viewing what you're actually submitting to the fab house, you can see exactly what they are going to deliver - be it good or bad. Review your gerber files before you submit! You'll save yourself time and monstrous amounts of money. If you want a $50 coaster, I'll sell you a truck full.

Zip these 7 files together and shoot them off to the fab house of your choice (Shameless Plug: we use BatchPCB). Depending on who you use and how deep your pockets are, you'll have to sit on your hands for 1 day up to 20 days. What do I do? I start other designs! While this board is being fabbed in 2 weeks, I create and submit a new design 7 days into it. That way I always have a new PCB proto coming in every few days. It's like Christmas every week! What am I getting this week? Is it going to work? I can't wait to test out my new cat tracker!

With the magic of television, I can jump 20 days into the future and show you...

In the flesh

It looks great! Time to whip out some parts and the soldering iron.

Assemble your new board!

Soldering was not too bad. Silkscreen looks good. Standoffs look good. Time for testing!

Always assume a proto will short out the first time you use it. Be very cautious and be ready to kill power immediately. Plugging this board onto the computer - guess what happens?

Uh-oh

What went wrong? Nothing is heating up. Nothing smoked or popped. The FT232 IC doesn't seem to be enumerating onto the USB bus. But why? Let's check the schematic one more time...

FT232 Breakout v1.0 Schematic

Son of a... This is why we prototype! Mistakes like this happens to the best of us. What is the problem you ask? Checkout the GND pin on the USB connector. It's not connected to anything. Without a ground connection to the board, no current can flow, the FT232RL will never enumerate. The board is shot! Or is it?

The green wire fix

(I know the wire is not green, but this is the nick-name for an oops! fix) This is my final thoughts on PCB layout - anyone can layout a PCB, but it takes a true magician to get a bad PCB working. Scratch, cut, splice, and otherwise modify your PCB until you get it working. This example was an easy fix. I've seen some really impressive fixes over the years.

From the SFE PCB History Museum

Don't immediately throw up your hands and layout a new board. Instead, make sure you get every bit of the functionality of your board working, by any means necessary, and then make all the revisions. Otherwise, you'll constantly spin your wheels with PCB revisions.

Things to remember:

Be sure to save your schematic as a new file name: *-v11
Be sure to update the date code on the board
Be sure to update the silkscreen on the board

Updated v1.1 schematic with GND connection on the USB connector

Updated v1.1 board layout with new GND connection, updated silkscreen and date code

Beginning Embedded Electronics - 8

2009-05-15T03:52:00.000-07:00

Lecture 8 - Eagle: Schematics

Welcome to the wonderful world of PCB creation! We've used a few software packages over the years (namely Protel DXP) and have found Eagle Layout Editor from CadSoft to be very easy to use, very cost effective, and very powerful.

Eagle is free! There are some limitations in place, but basic students and non-profit groups can use it. Protel is currently about $12,000 a seat.

Eagle is not the 'hobbyists' tool you may think it is. I've seen some very complex 8-layer BGA boards going into a firewall/router consumer product. I too was amazed to hear it was created in Eagle. It can be done, you just need to dream up the device!

There are a few files that you will need to download for this workshop.

Download Eagle itself. Currently we use v4.16 (~8MB). Versions are available for Windows, Linux, and Mac. If the above link does not work, google ’eagle pcb download’ to get the latest version.
Download the SparkFun Eagle Library. This is the collection of all the components SparkFun designs with and therefore components and footprints that have been tested. Unzip and place the SparkFun.lbr file into the Eagle\lbr directory. If the above link does not work, google ‘sparkfun eagle library’ to get the latest collection.
Download the SparkFun Eagle keyboard shortcuts. Place this file in the Eagle\scr directory. If the above link does not work, google ’sparkfun eagle shortcut’.
Download the SparkFun CAM file. Place this file in the Eagle\cam directory. This file is responsible for creating the gerber files for submission to a PCB fab house.

Note: The SparkFun Eagle shortcut key script file has an .scr extension. This is a common virus infiltration method. If you choose to download our keyboard shortcuts, and you don't trust us, rename the file to a .txt extension and view it in a text viewer. There's nothing there but text and Eagle commands. Just be sure to rename the file to the .scr extension so that Eagle will use it.

To learn how to use Eagle, we are going to create a simple breakout board for a popular USB IC. The FT232RL is a USB to TTL serial converter.

What is a USB to TTL converter?

Once the FT232RL is attached to the USB port on your computer, you will need to install some simple drivers (available for Windows, Linux, Mac), and then you will see a Virtual Com Port (VCP) appear on your computer. You can then use hyperterminal to open this new com port number. Any letters that are typed in hyperterminal are converted to a USB packet in the background, sent down the USB cable to the FT232RL where it reconstructs the serial information and passes these letters out the TX pin on the IC at whatever baud rate you choose. If you have a device connected to this TX pin, it will hear the serial letter and react. This will effectively give your device USB connectivity and you won't need to know a thing about how USB actually works!

This IC is very popular, but only comes in surface mount device (SMD) packages (sound familiar?). So let's spin a simple PCB that will allow us to use this handy IC.

When in doubt, follow the manufacturer's recommended circuit. This 'typical' application is just what we need.

This is a bare-minimum feature setup for the FT232R. Just what we need for simple TX/RX to USB. We want to plug the FT232RL on to the USB port, have it bus powered, and possibly power the rest of our circuit. Our ATmega8 uses 5V so we'll tie VCCIO to the USB 5V. A USB connector, a couple 0.1uF caps, a bigger tantalum cap, a ferrite bead, this doesn't look so bad!

Before we can get started, we need to create or locate a library part for the FT232RL. I really don't like using other people's footprints and schematic parts but in this case, FTDI has created some free libraries for their parts. This page should have the Eagle library (search the page for FT232RL) but if not, google 'ft232rl eagle footprint'. We also have this part proven in the SparkFun.lbr library. Use their library, use ours, create your own, it doesn't matter. But because we are most comfortable with our own parts (we know they work!) we will be using the SparkFun.lbr file for this tutorial.

Now let's add the FT232RL part to our schematic. Close the library editor and go back to the Eagle Control Panel. Click on File->New->Project. Name this new project 'FT232-Breakout'. Right click on the FT232-Breakout project and create a new Schematic:

The schematic editor should open. Now go back to the Eagle Control Panel and expand the SparkFun Library:

You should see a long list of parts. Highlight the FT232RL-Basic part and in the right screen click on ADD. The schematic editor will pop up allowing you to place the FT232RL.

Now save your schematic!

I like to use a board name and a version number within the file name. -v10, -v11, v12, etc as 1.0, 1.1, and 1.2 advance through layout changes.

Now add these other items to your schematic:

1 x FRAME-LETTER : This will add a nice frame to your schematic. Add all parts inside this frame.
3 x CAP (Device name CAP0603) : 0.1uF/0.01uF 0603 capacitors
1 x CAP_POL (Device name CAP_POL1206) : 10uF tantalum capacitor
1 x INDUCTOR (Device name INDUCTOR0603) : Ferrite bead
4 x STAND-OFF( Device name STAND-OFF): This part will add a hole and a keepout ring for a #4-40 screw. These can be used to raise your board up off a surface or to mount your board to an enclosure.
USB (Device name USBPTH) : USB Type B through-hole connector
M04 (Device name M04PTH) : Four pin 0.1" connector
GND (Device name GND) : Ground connections
VCC (Device name VCC) : Power connections

Parts added to the schematic

You can click on the button you need on the menu on the left side of the screen. You can also hover over each button and its name will pop up. This works great for beginners but as you advance, you'll want to speed up layout by using keyboard shortcuts. Here are some of the basic quick keys:

Press escape at any time to stop the current action and return to the schematic window
F7 to move a part
Alt+F7 to group a bunch together
F3 to delete a part
F4 to rename a part (change C7 to C2)
F5 to re-value a part (change 0.1uF to 10uF, etc)
F6 to smash a part (be able to move the name and value tags)
F9 to start a wire
Alt+F9 to add a label to a wire

NEVER change the grid size in the schematic editor. Leave it on 0.1inch steps and don't use the alternate 0.01 step. If you do, you won't be able to hook wires to the pin tie points.

Now we just need to begin wiring nets. Arrange the pieces so that there is as little net overlaps as possible.

Primordial FT232RL breakout

To wire a pin (TXD) to a far point (the 4-pin connector for example), instead of sending a wire half way across the page, we use net names. The green wire is not physically seen on the schematic, but Eagle knows to connect the two points on the layout because the two green wires have the same name.

Press F9 and click on pin 1 (TXD). Bring out the net a couple square widths and left click again to end the net. Press Alt+F9 to name the net. Click on the wire you just created. You should see a net name (like N$5) appear and be floating. Anchor it to the wire and TX pin:

To change the name on the N$5 wire, press F4 (Name command) and click on N$5. A window will appear - type 'TX' and press return. The TX pin should be correctly labeled and we have a few of the schematic connections.

To rename a device (change U$1 to U1), press F4 and then click on the device you want to rename. This also works to rename a net.

To change the value of a component (0.1uF to 10uF) press F5 and click on the device you want to change the value of. To move a device, press F7 (move command) and click on the device you wish to move. Now with a little renaming and rearranging the various components:

We've thrown a 4-pin connector into the schematic and used a very stripped down schematic symbol for the FT232R. For the purposes of this tutorial, we really only care about VCC/GND/TX/RX - the bare minimum. If you need access to more of the pins, use the more complete FT232R symbol and break them out!

Use the mirror command and rename the 4-pin connector (press F4 to rename a device):

Eagle files / PDF

I probably could have wired JP1 directly to the various pins but I wanted to demonstrate the net/name properties. This will also make it easier to label the pins on the PCB. Speaking of which, if you have not already, click on the 'Board' button to open the PCB editor:

All right! We've got the components onto a board and most of the nets connected, time for PCB layout!

How to copy and paste in Eagle Schematic:

This is perhaps the most counter intuitive part of Eagle. As with any new technical software, it's like learning a new language. Once you know the intricacies, you'll love it.

To copy one thing within a schematic is reasonably simple. Click on the 'Copy' button, then click on the thing you want to copy and that thing (component, wire, net name) will be duplicated and floating under your cursor. Drop it wherever you want it.

To copy a group of stuff within a schematic is completely wacky. First click on the group command:

You are going to create a frame around the stuff you want to group together. Left click and hold on one corner. Drag to the opposite corner. Now release the mouse button. The items that are part of the group should now be highlighted like this:

Now click on the Cut button. I know you don't want to delete these items - this is just how it works. Click on cut, move your mouse cursor to the middle of the group, and left click. Nothing happened right? That's okay. The group of items has been copied to the buffer. Now click on the paste button:

You should now have a copy of the group of items floating around. Drop these items wherever you need them in the schematic, or hit escape to return to the schematic window. I know, very odd but this type of group/modify steps comes in very handy over time.

Beginning Embedded Electronics - 7

2009-05-15T03:47:00.000-07:00

You can get all the parts for this lecture here.

Remember, 'Yes, I really can solder that'. It's time to put Simon together! This SMD kit will show you just what it takes to solder SMD components.

The SparkFun SMD Soldering Workshop is a pseudo-class that we've been working on at SparkFun. We hand out some paper materials and teach people these lectures and have them assemble a Simon kit. It's a lot of fun! You can download the handout here that contains the following material and a bit more.

Here are the various files you will need:

Simon Assembly Procedure (follow the steps!)
Simon Board (component print)
Simon Eagle Files (for trouble shooting)
Simon ATmega168 Firmware (for programming)
Simon (Old) ATmega8 Firmware (for programming)
Simon Schematic (for general reference)

Here is some good information for SMD soldering:

SMD Soldering Basics (big 4MB)
SMD Soldering Workshop

Here is some basic code examples to show how to control various parts of the Simon board:

Basic Simon Control

For more soldering tutorials, there are some great videos and instructions on the SparkFun website here. Read up on those basics as well.

Two words : solder wick. Get some. Actually, get a lot.

Simon SMD Kit

This is what we will be assembling today.

Assembled and blinking!

Make sure you've got all the components you need. Remember, SMD resistors are marked, capacitors are not so be sure to correctly identify the caps by writing on the tape immediately after you cut it off the reel. If you've just got a Digikey bag, make sure the correct components make it back into the correct bag.

Through-hole components:

1 x Simon PCB
2 x AA Battery Clips
1 x Buzzer
2 x Slide switches
1 x ISP Header
4 x LED (Yellow, Blue, Red, Green)
1 x Momentary Push Button
6 x Screws
6 x Plastic Standoffs
1 x Rubber 4-Button Pad

SMD components:

5 x 10k Resistors
4 x 220 Ohm Resistors
1 x 47uF Capacitor
1 x 10uF Capacitor
1 x 0.1uF Capacitor
2 x 22pF Capacitor
1 x 16MHz Crystal
1 x MBRA140 Diode
1 x 22uH Inductor
1 x NCP1400 SOT-23-5 IC
1 x ATmega168 TQFP IC

Parts and assembly sheet

We created an Eagle shortcut button to help us produce assembly sheets. Pressing Alt+F11 will turn off all the extraneous layers, and turn on only the layers we need for assembly purposes. Pressing F11 will turn all layers back on.

All layers vs. assembly layers

Once you have just the assembly layers turned on, you can print the assembly sheet. I like to scale this print out by 3 so that the printout is 3 times larger than actual size. This helps when writing component values next to tightly packed components. With the printout in hand, write in all the pertinent component values so that you know what goes where.

When soldering a mix of through-hole and SMD components, always start with the smaller, tighter pitch devices. If you go jumping into the easy ones (the power switch, LEDs, ISP header, etc), you will run the risk of touching the iron against these larger plastic items and melting them. Let's start with the power circuit:

The first thing we are going to build is the DC to DC step up power supply. This will take the 1.5V from the AA battery and boost it to 5V.

NCP1400 surrounded by inductor and diode

Be sure to start with the inner most parts and work your way out. Otherwise, it can be difficult to get the iron into tight spaces.

Let the videos begin!

Clean your iron on the wet sponge. Place a blob of solder on one or two pads on the PCB. Slide the component into the blob and remove the iron. If the IC is not lined up, or is not flat against the PCB, heat the blob back up and re-align the IC square and flush against the PCB. You can do this 3-4 times before you start to thermally stress the PCB.

Once you have the IC to your liking, solder the other pins. Don't worry about jumpers.

If you have jumpers, pull out the solder wick. Watch the video closely! First I put a blob of solder on the end of the iron, hold the wick over the jumper, then I hold the iron w/ blob against the wick. You will notice a change in color of the wick - this is the solder climbing the wick! The blob on the iron aids in transferring heat and flux to the wick and jumper. After a few seconds, the blob travels up the wick and pulls the jumper along with it. Remove the wick along with the iron (do not remove the iron and allow the wick to attach to the component). The jumper is removed.

Not so bad, right? Now let's solder the diode.

Add solder to one pad. Make sure the white mark on the diode lines up with the bar on the silkscreen. Slide the diode in, hold it in place while you remove the iron. If alignment looks good, solder down the other end.

NCP1400 with inductor and diode

The inductor requires a bit more solder and patience. The footprint is pretty tight. Make sure you slide the inductor all the way over your first pad so that you can solder the 2nd pad.

Solder on the 10uF cap and 47uF cap. Make sure you get the polarization correct. Solder in the power switch.

Solder in the AA battery lugs. They will require a bit more heat and time because they act like heat sinks. Once you have all these power components attached, insert a AA battery into the power clips. Be sure the '+' and '-' signs on the board match up to the battery.

Whip out your multimeter, cross your fingers, flip the power switch to 'On', and measure the voltage across the 47uF capacitor. It should read approximately 5V. 4.8V to 5.2V is fine. If you read something much lower, turn off the board immediately and check to see if anything is warm. Check your polarization of components (diode, caps, and battery). Check to make sure all the solder connections are sound. Touch up as necessary and re-test. Make sure you've got a solid 5V supply before moving on. Remove the battery to prevent accidental turn on during soldering.

Time to solder the ATmega168!

Same steps: put a blob of solder on one or two pads as the anchor. Slide the IC into the molten solder and align the IC. Once you have everything square and flush against the PCB, remove the iron. Do not worry about jumper, but do not solder more than 2-3 pads while you are doing this alignment step.

Soldering Side 1: Now that you've got the IC in place, jumper the opposite side like crazy. Make sure each pin gets heat/solder. Then go back with wick and wick away the excess.

Soldering Side 2: More of the same. Jumper, and wick away.

Soldering Side 3: If the wick starts to get in your way, cut off the used wick (once it's silver, it's not re-usable) and throw it away.

Soldering side 4: Same motions, but two of the pins should already have a jumper. Add solder to all pins like before, and wick away the extra.

The ATmega168 should now be soldered! Congrats! That was the hardest part! Let's solder the crystal next.

Add solder to an anchor pad, slide and and align the crystal so that you can see equal parts of all four pads. Solder the other four pads. Be careful not to allow solder to jumper from the pad to the top cover. The crystal packaging is ceramic (non-conductive) but the top is metal and will short pads together if you're not careful. This shouldn't harm the crystal, it just won't oscillate.

0603 Resistor pinned down

Now we have a handful of discretes to solder down. Be sure you get the 220Ohm, 10k Ohm resistors, 22pF, and 0.1uF capacitors in the correct places. They are not polarized.

Add solder to one pad (in the picture above I've added anchor solder to all components on the board), slide the component in, and remove the iron. Add solder to the 2nd pad. Add solder to the first pad if you want, to try to minimize the 'horns'.

220Ohm 0603 resistor all happy

Continue soldering all 0603 components.

Close-up of the ATmega168

Don't worry about the gunky brown stuff too much. That's residual flux and can be cleaned off with a little rubbing alcohol if it bothers you.

Now it's time for the easy stuff! Soldering in the through-hole components!

Use the weight of the PCB to hold the ISP connector in place. Be sure to solder the ISP connector so that the long pins point up when looking at the front of the board. You will be soldering from the back of the PCB. Tack one pin down and check that the ISP connector is flush against the PCB. If it's not, re-heat the one pin while lightly applying pressure to the connector/PCB until they are flush. Now solder the other 9 pins, finally touching up the original anchor pin.

Ground pins will require extra time/heat. Don't get speedy. Childs play compared to SMD components, right?

Now insert and solder the reset switch. The reset switch should lock into place so just make sure it's flush before soldering it.

Repeat these steps for all through hole components (sound switch, buzzer, etc).

Almost there!

Notice we have not yet soldered in the LEDs. Because they are clear, we don't know which LED goes where. Also, we've been tricked in the past by mistakenly marked LEDs (the flat mark on the LED did not correctly match with the silkscreen). We first need to program the board with Simon game firmware and then hold the LEDs in place for testing.

First step - add some stand-offs. This will levitate the board above your work area and avoid the possibility of shorting bits of scrap wire across the back of your PCB. Insert the AA and make sure we still have 5V on the board. If not, immediately disconnect power and check for shorts. Continuity probe if necessary. Now attach the AVR-PG2 programmer and open Programmer's Notepad as we did in Lecture 2. The AVR-PG2 programmer requires power from the board so be sure to turn on your board before attempting to program.

We will need to configure the ATmega168 to use its external 16MHz crystal. ReviewLecture 3 and in a command prompt send:

avrdude -p atmega168 -P lpt1 -c stk200 -U lfuse:w:0xff:m -U hfuse:w:0xc9:m

If the fuse programming throws an error (it always does on the first try for some reason), select 'n' and try again. The second time, it should complete successfully.

Here is the firmware for Simon for the ATmega168. Open Simon.c in PN2, select Tools->Program and the firmware should load onto your Simon board. Now insert one of the LEDs and hold it slightly at an angle. It should light up momentarily. Turn off Simon. Whatever color the LED is, insert it into the appropriate place on the PCB, bending the legs once it's flush against the PCB to hold it in place. Solder this LED in place and repeat these steps for the other three LEDs. If the LED does not light up, flip the LED around to see if it's an orientation problem. If the LED still does not light up, check to make sure the firmware is loaded correctly.

Once you have all four LEDs soldered in place and blinking correctly, add the button pad and secure it in two places with a screw and standoff.

Simon!

You should now have a functioning Simon game! Congratulations!

Now if you are the lucky type that runs into problems during assembly/testing, there are a few things that should be checked. In order of priority:

Test for shorts between VCC and GND
Check that the board has 5V
Test ISP pins for shorts to GND, or shorts to VCC
Probe connections from ISP connector to given pins on ATmega168
Probe connections from pins on ATmega168 to various components

If any one of these steps fails, you should be able to localize the problem and cut traces, green wire, whatever it takes to get the PCB working.

for further details go to

http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=107

you can find all the videos in the above mentioned link...

Beginning Embedded Electronics - 6

2009-05-15T03:45:00.000-07:00

Say it with me - 'Yes, I really can solder that'. Yes, you really can solder that and anything else.

First, we will solder a through-hole component kit. Here are the ground rules for soldering:

Rule 1: Irons get hot. Don't poke your lab partner in the eye with it.
Rule 2: You need to wet your sponge. This may seem counter-intuitive, just do it. I hate seeing people ruin irons because they're too lazy to get the sponge wet. This wet sponge is used to clean the corrosion on the tip of the iron. A dry sponge does nothing but damage the tip. Every time you pull the iron from the stand, it's a good idea to swipe the tip on the sponge just to clean it off and get a nice silver tip - it will allow you to solder much quicker and much cleaner.
Rule 3: The point on the iron-tip is NOT the hottest part. This takes some practice but learn to use the side of the tip near the point. It's all about getting the heat to flow from the iron to the joint. If you sit in one spot for a long period of time and nothing is flowing, take a step back, clean your tip, add a bit a solder to the tip, and try soldering the joint again.
Rule 4: The soldering iron is only there for heat, not solder. You use the iron to heat two things - the part and the board, and then you add solder to the two heated parts. You do not add a glob of solder to the tip and then rub this mess against the two things you're trying to solder together. Use the side of the iron (remember, not the point) to heat the two parts while adding solder from the opposite side.
Rule 5: Perfectionism kills. If you solder a joint, and it looks alright, let it be. Do not solder, then touch up, and re-solder, and then have to touch up a third time. This heating/reheating stresses the PCB (printed circuit board). You will quickly delaminate the board, lifting traces, pads, and destroying the board. Do this for fun on your own time.
Rule 6: This is really getting ahead of ourselves here, but it's good to hear as many times as possible. When soldering joints that have a lot of thermal weight, heat the joint up for an additional 5-10 seconds. When you solder to a big part or a pad that has a lot of copper attached to it (very common with GND connections), it takes a few extra seconds for the iron to pump enough heat into the part to get it to the correct temperature to form a connection. If you notice your iron tip feels 'sticky', or if you see the solder balling to the pin instead of flowing to the joint, this is because one part of the joint is not hot enough. Hold the iron on the joint for a few extra seconds and allow the solder to flow correctly.

Here is a short video to demonstrate how to clean your iron tip, solder a through hole component, and clip off the extra leads.

Now about irons:

This is my cheap-o Sunkko iron. It was under $100, it can solder lead-free solder just fine, and I use the standard included iron tip. You don't really need a digital read-out for home use, but do get an iron that has an adjustable temp dial. I set mine temp to about 350C for leaded solder. Notice my sponge is wet!

A cold iron tip. You can see the barrel and upper area of the iron are discolored by heat over time. No problem. You do not need an needle-sized iron tip to solder SMD devices. This is a common fallacy. This tip works very well!

Here's my solder. I stole this from work because 1) It's leaded and we use lead-free for production. 2) It's 0.020" diameter which is really too thin for production. Because it's so thin, the assemblers would have to use many many inches of solder to solder larger joints (like DB9 connectors). Smaller diameter solder helps you control how much solder goes into very tight pitch joints but it's not magic - it is not required. Just don't buy the solder at the hardware store that they sell for copper pipe plumbing, that stuff is ridiculously thick.

This solder is SN63PB37 meaning it's 63% tin and 37% lead. It's also called 'rosin core solder' because it has an organic core of rosin. As you melt the solder into the joint, a small amount of rosin inside the core will come out and help the solder flow. Rosin basically changes the surface tension of the solder allowing it to flow better (we're talking about liquid metal after all). Rosin will burn off and that's the small amount of smoke you see while you're soldering. Standard rosin smoke is not harmful! It has been known to irritate some people's eyes but I've never known anyone to have a problem with it. When in doubt, get a fan or open a window. Lead is known to be a carcinogen. In general, don't eat the solder. Wash your hands before you eat and you should be safe.

This is a 1lb spool which should last me until 2020. $18.95 from JB Saunders. JBSaunders is a surplus shop in Boulder, CO. They sell some handy tools and supplies but it's not your standard hobby shop - it can be tricky to get help some days. Solder aficionados may watch the DOM (date of manufacture) and claim that solder will go bad at some point. I have no idea. I imagine the rosin may change slightly over time but this solder is probably good for many years to come.

Here is a hot iron, with a blob of oxidized solder on the tip.

A quick double swipe on the sponge and the tip is clean and shinny. This is the iron you should be soldering with! Keep your tip clean and shinny. Clean it often. Wipe it on the sponge every time you take it out of the base. Add a bit of solder to the end of your cleaned tip to increase heat flow

That's the starters. Soldering takes practice! Just go and get your hands dirty already.

The Shifter board assembled

You will be assembling the 'Shifter board'. (Please note: the component placement on the shifter board in the photos in this tutorial might not be the same as the shifter board you purchase. Make sure to follow the silkscreen indicators on the board you receive for proper component placement.) This board is a MAX232 equivalent circuit meaning it does some dirty tricks to convert RS232 signals to TTL level signals. It does this with a few pennies worth of parts instead of a proper MAX232 IC.

The benefits of the shifter board vs. a conventional MAX232 circuit:

The shifter board is smaller than a MAX232 DIP with its charge-pump caps
Cheaper
Works at voltages down to 2.5V (compared to the MAX232 that only works at 5V)

Problems with the Shifter board:

It's a bit dirty, meaning it does not follow the proper RS232 +/-12V convention (shifter board only puts out -3V to +5V)
It will not operate faster than 115200bps (some MAX232 ICs can operate up to 1 mega-bit per second)
It only has TX/RX where a MAX232 has TX/RX/CTS/RTS (additional control lines)

In response to problem 1 - I've never come across a modern computer that the shifter board does not work. This is because the RS232 ports on modern computers are designed to deal with poorly designed serial devices! So even though our shifter board can't quite get to the -12V and +12V, the computer can still understand what it's trying to say.

Problem 2 - Windows simply can't handle serial speeds faster than 115200bps (well, not without some serious finagling). The shifter board works fine at this speed so the MAX232 has no real advantage for the every-day application.

Problem 3 - Almost all the serial interfaces you will be building, hardware flow control (CTS/RTS = clear to send and ready to send) is rarely used. The shifter circuit is simple. Replicate it twice if you want flow control.

So let us build up this kit and replace the MAX232 circuit in the breadboard with our shifter circuit. Always lay out all your parts to make sure you've got everything you need.

Plated through-hole (PTH) resistors have color bands on them. Surface mount device (SMD) resistors have readable numbers on them. I can't read the color bands on resistors to save my life, but your multimeter can! The shifter kit is easy to tell which is which - there are five 10k resistors and two 220Ohm resistors.

Resistors are non-polarized meaning they can be inserted into the board either way. You can pre-bend the resistor leads if you like. After the resistor is inserted into the board, bend the legs out the other way so that it stays in place. Pull out your iron and solder the resistor from the bottom side of the board.

Hold the iron against the PCB and the leg of the component. Insert solder into this trio. It should melt as you add it. If not, re-orient the iron to get better heat conduction. It's not hard, just practice. Once you've got the two joints soldered, clip off the legs.

Clip off the legs. Don't worry about clipping the legs absolutely flush. Doing so can stress the mechanical nature of the joint and the PCB.

The kit has various indicators showing the assembler how to orient parts. Pay close attention to these and the resistor values.

Notice the small pool of solder at the base of the resistor legs we just soldered in? This is good. Enough solder was applied to come through the holes from the bottom of the board to fill all the way through the via.

The single diode in the kit is polarized so you'll need to get the orientation right. In the picture above, the black line on the diode matches with the white line on the silkscreen.

Soldering the diode like this would be bad. Make sure you get the component flush against the PCB, within reason. Some components (like the transistors we're about to solder) ride above the PCB. Solder up the rest of the resistors.

All the resistors and diode

Soldered and trimmed. Notice the small amounts of residual flux - it's the clear, shiny, sticky material left of the board. For production assemblies, this flux is cleaned off with a light solvent or rubbing alcohol. Flux is slightly acidic and will degrade solder joints over a period of years. For our purposes, this flux is ok and shouldn't cause any problems.

Solder in the electrolytic capacitor noting the '-' sign polarization matching with the silk screen.

LEDs installed. Note the flat side of the LED matches the silkscreen polarization.

Install the 2N3904 and 2N2906 transistors. Note the flat side of the BJT transistor matches the flat side of the silkscreen. Make sure you get the correct '3904' and '3906' labeled parts in the correct spot.

Here is a short video to demonstrate how to clean your iron tip, solder a through hole component, and clip off the extra leads.

Install and solder the DB9 connector.

You can see now why it would have been a bad idea to solder the DB9 connector first. The PCB would have been at an angle during soldering.

Solder in the four connection wires - VCC, GND, TX, and RX. Pick your own color scheme. I only recommend that red and black go to VCC and GND respectively.

The shifter board, all assembled!

Guess how we're going to test it? A loop-back jumper of course! Plug the shifter board into your breadboard, VCC and GND, and insert the TX/RX wires into one row, shorting them together.

Power your board, pound some characters into hyperterminal and verify that you get an echo. You should see the TX and RX LEDs blink briefly. Congrats! You now have a serial connection for all your future breadboard prototypes! This should open up some significant space on your breadboard and allow you to skip building a MAX232 circuit for future breadboard projects.

In the end, I use the shifter board on all my breadboard prototyping and a conventional MAX3232 circuit on my PCB designs. Sorry to confuse you so much. When you solder together as many prototype PCBs as I do, you really want to limit how many solder connections you have to solder. Inserting through-hole components for the shifter circuits takes much more time than a MAX3232 circuit. I also like the MAX3232 circuit because it has fewer parts that could break.

Beginning Embedded Electronics - 5

2009-05-15T03:37:00.000-07:00

Lecture 5 - AVR GCC Compiling

Sorry for the confusion. When these tutorials were written and photographed, we used the ATmega8. We now carry the newer ATmega168. You will find all ATmega168 information in the following pages, but the pictures will show an ATmega8.

I know very little about the ins and outs of the AVR-GCC compiler. I've learned a few basics that helped me along the way, but when you run up against a jam, google and AVRfreaks.net are your friend.

First, we did the blinky. Open this code in PN2 and make sure you can compile it. Click on Tools->Make All. The window in the bottom screen should say 'Process Exit Code: 0' meaning the compilation was successful. If not, there should be a line number listing of the problem line of code. Be sure to check above and below the indicated line for problems.

In the second example C file called basic-out-atmega168.c (basic-out.c for the ATmega8), I've inserted a handful of functions and lines of code. First of the black magic:

#define FOSC 16000000
#define BAUD 9600
#define MYUBRR FOSC/16/BAUD-1

What is all this noise at the top of the file? This is a series of defines that calculates the MYUBRR variable with the correct number. Since serial communication depends on the fact that we will be transmitting and receiving at 9600 bits per second, it's crucial to tell the ATmega168 what bit rate to set. Because the ATmega168 is dictated by the oscillator that it is using, we must correctly calculate what value we need to load into the ATmega168 hardware so that the ATmega168 sends the serial pulses at the correct rate with a given oscillator type. In our case, we are using a 16MHz oscillator so we can setup the define statement as shown. MYUBRR is calculated at compile time and is loaded successfully into the hardware UART during run time.

A reader's untested submission:

The UBRR value calculation in Lecture 5 could be more accurate with the following macro:
#define MYUBRR (((((FOSC * 10) / (16L * BAUD)) + 5) / 10) - 1)
There is also pretty useful web form for UBRR calculation:
http://www.wormfood.net/avrbaudcalc.php

static FILE mystdout = FDEV_SETUP_STREAM(uart_putchar, NULL, _FDEV_SETUP_WRITE);

This line creates a buffer for the printf statement to post to. I'd rather not explain it, simply because I don't understand it. When I am working on a new coding project I never start from a blank page, I *always* start from a known working program and slowly bring in bits of other projects to get the code I need, writing bits along the way. Please start from this printf example and build away. The purpose here is to get your printing string to the terminal window.

Checkout the ioinit() function. You'll notice some new commands.

UCSR0B = (1<

This is the really funky, but very practical, method of setting bits on the AVR series. RXEN0 is defined in some file as '5'. 1<

Finally, we see the very comfortable line of code:

printf("Test it! x = %d", x);

What did you say? This is not a comfortable line of C code for you? Ok - printf is somewhat of a universal function to pass serial strings and variables to the outside world. The line of code above will pass the string "Test it! x =" to the serial port and it should display on the terminal window. After that, the %d gets converted to an actual decimal number so that whatever digital number is currently stored in the variable x gets printed to the terminal screen. So what? This simple printf statement allows you to print variable contents and see what's going on within your C program.

Time to load the basic-out-atmega168.c file onto your breadboard. Open up PN2, compile basic_out-atmega168.c. Power up your board, click on Tools->[WinAVR] Program from within Programmer's Notepad. The code should now be loaded onto your ATmega168. If WinAVR throws a verification error, try again. Open up the terminal window at 9600bps if you don't already have it open.

Text output from the ATmega168 and MAX232 circuit

All right! We've got output from the ATmega168! Now let's talk about some more of the code:

sbi(PORTC, STATUS_LED);

Another funky one if you're not used to the AVR series. To toggle a GPIO pin (general purpose input/output pin), you need to read the state of the port, mask the bit change into the state-word, and then write the 8-bits back onto the port effectively modifying just the one bit. Instead of doing all that by every time you want to toggle a port pin, there's this handy macro:

#define sbi(var, mask) ((var) |= (uint8_t)(1 <<>

SBI sets a bit. CBI clears a bit. You have to specify which port you're working with and which pin you want to alter. Throw another define at the top of your code:

#define STATUS_LED 0

Now you can control your STATUS_LED on PORT C using these two simple commands:

sbi(PORTC, STATUS_LED);

To turn on the LED and

cbi(PORTC, STATUS_LED);

To turn it off.

You should have an LED tied to pin 23 on the ATmega168. When in doubt, toggle your status LED to figure out where the code is hanging or use a printf statement.

There are also some tweaks to the delay_ms() routine. Because we increased the oscillator from 1MHz to 16MHz, I increased the loop iterations to tie up the processor for longer. I didn't do any real calculations so don't depend on my delay_ms routine. delay_ms(1000) looks to be roughly a 1 second delay.

Open basic-in-atmega168.c (basic-in.c for the ATmega8) and load up your breadboard:

Key presses and various responses

Here we see that whatever character we hit, the ATmega168 responds with 'I heard : ' and the character. Also, if you hit return, X, or g, you will see various special output.

key_press = uart_getchar();

printf("I heard : %c\n", key_press);

if(key_press == 'g') printf(" GO!\n");
if(key_press == 'X') printf(" EXIT\n");
if(key_press == 13) printf(" RETURN\n");

uart_getchar sits waiting for a character to appear in the UART. Once received, the ATmega168 outputs the character (%c) and goes to a new line (\n). It then checks to see if the key press was one of three special cases. If so, it prints an extra string accordingly. I hope you are starting to see the power of the input/act-upon/output that a microcontroller is capable of. With a little bit of work, you could program your own text-based adventure game. Go to town.

Remember back when you were struggling to get your power supply wired up? Nice job! Time to heat up your irons.

Beginning Embedded Electronics - 4

2009-05-15T03:33:00.000-07:00

Lecture 4 - UART and Serial Communication
Hello, Hello World
You can get all the parts for this lecture here.
Sorry for the confusion. When these tutorials were written and photographed, we used the ATmega8. We now carry the newer ATmega168. You will find all ATmega168 information in the following pages, but the pictures will show an ATmega8.
The ATmega168 has tons of hardware built into it. Let's unleash the serial communication. Everyone has programmed the 'Hello World' program. You've got your micro breadboarded and running at 16MHz. You've got WinAVR up and running. We've already demonstrated LED control. Now it's time to pass some serial data back and forth.
I am not a huge coder. I just want my printf() statement to do what it is supposed to do. I don't use a hardware debugger, I debug by printf statements. Sure, there are limitations with this, but for 90% of the applications out there, debugging with printf statements works just fine.
First, a quick history of RS232. What is RS232? It's just a name for a standard that has propagated from generation to generation of computers. The first computers had serial ports that used RS232, and even current computers have serial ports (or at least USB ports that act like RS232 ports). Back in the day, serial information needed to be passed from devices like printers, joysticks, scanners, etc to the computer. The simplest way to do this was to pass a series of 1s and 0s to the computer. Both the computer and the device agreed on a speed of information - 'bits per second'. A computer would pass image data to a printer at 9600 bits per second and the printer would listen for this stream of 1s and 0s expecting a new bit every 1/9600 = 104us (104 micro-seconds, 0.000104 seconds). As long as the computer output bits at the pre-determined speed, the printer could listen.
Zoom forward to today. Electronics have changed a bit. Before they were relatively high power, high voltage devices. The standard that is 'RS232' dictates that a bit ranges from -12V to +12V. Modern electronics do not operate at such high positive and negative voltages. In fact, our ATmega168 runs 0V to 5V. So how do we get our 5V micro to talk the RS232 +/-12V voltages? This problem has been solved by the IC manufacturers of the world. They have made an IC that is generically known as the MAX232 (very close to RS232, no?).
The MAX232 is an IC originally designed by a company called Maxim IC that converts the +/-12V signals of RS232 down to the 0/5V signals that our ATmega168 can understand. It also boosts the voltage of our ATmega168 to the needed +/-12V of the RS232 protocol so that a computer can understand our ATmega168 and vice versa. To get our ATmega168 IC sending serial characters to a computer, we have to send these serial signals through a MAX232 circuit so that the computer receives +/-12V RS232 signals. Don't worry if you're working with a chip labeled 'ICL232' or 'ST232' - these are just generics of the MAX232. Everyone says 'MAX232' just like they say 'Kleenex' or Coke. The ICs all function the same and nearly all have the same pinout.
The MAX232 circuit that we will be breadboarding looks like this:
MAX232 Circuit - Eagle schematic / PDF
This MAX232 IC uses three 0.1uF capacitors (C5, C6, C7) to operate (go read about 'charge pumps'). You must have these installed. The forth (C8) is what is called a 'decoupling cap'. As the MAX232 IC switches various signals (from +/-12V to 0/5V) it uses bits of current. Because it needs these bits of current in bursts, it can disrupt your 5V supply. The C8 0.1uF capacitor helps 'decouple' or remove the ill effects of this IC (switching back and forth) from your power supply. This decoupling cap should be placed near the VCC and GND pins of the IC. This helps remove noise from your power system. Will your breadboard work without decoupling caps? Sure it will! Go without! But the day will come when something stops working and you're not sure why. Could it be my code? Do I have a short somewhere? A disconnect? Or perhaps I don't have enough decoupling caps?
A decoupling cap is meant to provide a quick burst of energy if the power supply dips down - sort of like a UPS system for your IC. The further the decoupling cap is from the IC, the less ability it has to provide that quick burst (long wires have intrinsic capacitance of their own). It's always good engineering practice to have at least one 0.1uF cap near any IC. Placing them within 0.5" of the VCC and GND pins is good. Placing them all the way across your breadboard won't do harm, they just won't provide as much help.
JP2 is a DB9 connector. It's called a 'DB9' connector because it contains 9 pins and is used universally for serial connections. You'll need a male to female serial cable to connect your breadboard's DB9 connector to the computer. The 'male' end of the cable has the metal pins, the 'female' end has the black colored plastic that receives the pins. If you look very close at a DB9 connector in real life, you can just make out some small numbers next to the holes.
So what all does this do? The ATmega168 is going to send 5V signals to the MAX232 IC. The MAX232 IC in turn will convert those 5V signals to +/-12V RS232 signals that the computer can understand through the DB9 port on the back of the computer. Admittedly this can be a bit ugly to setup at first. Will you believe me that once setup, this will be your life-line to sanity? The serial connection is everything! You'll need one on almost every application you do.
Breadboard with MAX232 and large loop-back jumper installed
Once you have everything wired, you'll need to open up a terminal program. If you're playing under Windows, you can open up the included 'Hyperterminal' program normally located under Programs->Accessories->Communications. Linux and Apple people, you probably know how to get a terminal program running (sorry I can't be more help!).
All terminal programs have the same basic function: to do serial. All you need to specify is a few simple rules to get your micro playing successfully with your computer. Let's just get through the Hyperterminal screens:
Call it whatever you want
More than likely, the serial port on your computer is COM1
You want 9600bps 8-N-1 without flow control
The main settings are 9600bps and 8-N-1. This means that the micro and the computer agree to talk at a rate of 9600bits per second (bps) and that each byte will have 8 data bits, with no parity bit, and only 1 stop bit. This '8-N-1' is very common and basic. If you like pain, go read about parity, 1.5 stop bits, and 5 data bits. No one really uses it in the breadboarding world.
Mkay, you've got hyperterminal open and kicking. You've got your MAX232 (or equivalent circuit) built up and powered on. Before you connect it to your micro, you should test that the MAX232 circuit works. The easiest way to test a MAX232 circuit is to tie TX and RX together. It's called a 'loop-back' (the big yellow wire pictured above). Pretty self explanatory, but just follow along:
When you press the 'A' key on the computer in the hyperterminal window, a series of 1s and 0s get generated and pumped out the serial port on the back of your computer (8 bits: '01000001' to be specific = 65d = 41h - see www.asciitable.com for more info). These 0s and 1s hit the MAX232 on your breadboard which dutifully changes these RS232 signals to TTL signals. The 0s and 1s get asserted on the R1OUT pin. Because you've tied the TX and RX pins together (R1OUT should be shorted to T1IN) these 0s and 1s get sent right back out the MAX232 and down the DB9 serial cable. Upon hitting the computer, the computer 'sees' these 1s and 0s and says 'oh! there is a device passing me the ASCII character A'. The computer then displays the character 'A' in the hyperterminal screen. This is the essence of a loop-back test. If everything is kosher, you should be able to jam away on the keyboard and see those letters echoed back to the terminal window. Pull the jumper out and the characters should stop echoing. Got it? Use it! In the future, when you need to test a serial interface, short TX and RX together to make sure things are working correctly.
All right, you've got the MAX232 working correctly. Now connect the TX and RX pins of the ATmega168 to the MAX232 circuit.
ATmega8 with power supply and MAX232 circuit. Eagle schematic / PDF
You may have noticed C9 magically appeared next to the ATmega168 in the schematic above. This is a 0.1uF decoupling capacitor for the ATmega168. A 0.1uF capacitor places near the ATmega168's VCC and GND pins will help reduce power supply noise being injected into the ATmega168. Again, your board will more than likely run without decoupling caps but I just want to instill in you a habit of using 0.1uF like candy.
TX and RX connections between MAX232 and ATmega8
Savvy travelers will note (upside down) the picture MAX232 IC is actually a SP3232(EBCP). What is this 'SP3232'? It's a the Sipex generic of the MAX232. Notice the '3' in front of the 232? The original MAX232 ICs were designed to interface 5V logic to RS232. Because circuits started to run on lower voltages (3.3V for instance) the IC manufacturers had to redesign the MAX232 ICs to be more efficient so that they could take this lower voltage and boost it up to 12V for RS232. Hence the 3V designation 'SP3232'. This IC can input 3V TLL signals and successfully convert them to RS232. We are operating our breadboard at 5V but we are able to run our MAX232 from 3V up to 5V without problems.
Trivia: In the picture above, which IC is the older sibling? These ICs have simple date codes: 0641 and 0625 means both ICs were manufactured in 2006 in the 41st and 25th weeks of the year.
You should now have the hardware in place to allow you to do printf statements. Let's mess with some code!

Beginning Embedded Electronics - 3

2009-05-15T03:30:00.000-07:00

Lecture 3 - What is an oscillator?
You can get all the parts for this lecture here.
Sorry for the confusion. When these tutorials were written and photographed, we used the ATmega8. We now carry the newer ATmega168. You will find all ATmega168 information in the following pages, but the pictures will show an ATmega8.
You've got the LED blinking on your ATmega168 - congrats! That's a huge step. Now it's time to make it blink faster!
You loaded code onto the chip and the ATmega168 is running that code, but how is it running? And how fast? Any micro needs a clock source. Think of it like a a type of 'musical beat' that the micro uses to to execute its code in a set manner. Without a clock, the micro doesn't know how to run the code, and with a sloppy clock (one that varies a lot) the code runs at an undetermined rate. You must have a clock of some sort and sometimes you need a very accurate clock. You ever try dancing to a CD that skips? It can be very hard!
There are many ways to generate a 'beat' for the microcontroller. The ATmega168 gives many options. Here is a quick breakdown of the different types of beat generators:
External RC - This is generally used for *very low cost* applications. Using a resistor and a capacitor, the charge/discharge rate can be used as a clock input. I've never really used this type of clock.
Internal RC - This is the super cool oscillator. Found on newer micros, you can just ask the ATmega168 to generate its own clock! The silicon has a built in oscillator. Unfortunately it's not very accurate.
External Oscillator - The is the defacto standard. Attach a quartz crystal ('crystal' for short) to the two osc pins and the code executes at this given frequency.
External Resonator - A resonator is a bit cheaper than an oscillator but has worse tolerances.
External Clock - Instead of an oscillator, you can use a powered clock driver. Handy if you have multiple devices that need to run on the same frequency. I've never used this option.
For some great information about clock sources and their uses, checkout this app note fromAVRFreaks.
I really only use 3 out of these 5 options so I'm going to delve into them more:
Internal RC -
Atmel is very smart! They ship the ATmega168 preconfigured to use the 1MHz internal oscillator. The ATmega168 (and AVRs in general) can operate at 1 instruction per clock cycle. This means that every time the oscillator goes through one cycle, one instruction is completed (this is roughly true - there are some instructions that take more than one clock cycle). Because we are using stock ATmega168s, we are running the blink code at 1MHz or 1MIPS (million instructions per second). You read that right - 1 million things a second! That's pretty impressive. What's the problem with the internal osc? It has a tolerance of +/-5% and a max speed of 8MHz. +/-5% tolerance means your ATmega168 might run at 1,000,000 * 1.05 = 1,050,000 IPS while your neighbors' ATmega168 runs at 1,000,000 * 0.95 = 950,000 IPS. This may not sound like much difference but in the digital world, this is huge! Also, the ATmega168 has a max speed of 20MHz (the internal osc runs max up to 8MHz) so if you really wanna push this IC to the max, you'll need a to use an external oscillator.
External Oscillator -
This one is most common type of clock source.
Quartz crystal oscillators come in all different flavors and frequencies. Some of the more common freq are 20MHz, 16MHz, 10MHz, 4MHz. There are also some frequencies like 14.7456MHz, 9.216MHz, and 32.768kHz that are available because these frequencies are multiples of speeds needed for serial communications and for timing. For example - if you need really accurate 9600bps serial communications, 9.216MHz divided by 960 = 9600. There is no integer that divides nicely into 16MHz to get 9600. So serial communications at 9.216MHz will be very accurate while serial at 16MHz will always have some small amount of error.
Inside the metal housing is a small piece of quartz crystal that has been precisely cut in size so that the piece of crystal vibrates at a specific frequency. The ATmega's internal osc was +/-5% tolerant. On the other hand, a crystal is normally '+/-20ppm'. This means the frequency is accurate within +/-20 parts per million! So you might have a 16,000,020MHz crystal while your neighbor has a 15,999,980MHz. This is equivalent to +/-0.00000125%. The crystal is 4 million times more accurate than the internal oscillator!
Technical note: Sorry to swamp your brain with nitty gritty details, but this is reasonably important. The silver metal device shown above is a crystal. It is not technically an oscillator. Crystals are cheap. True oscillators are expensive ($2-$4 range). What is the difference? An oscillator uses power and creates a true frequency pulse. This pulse can be used to drive all sorts of peripherals. A crystal is a purely passive device that requires some external drivers to get it to become an 'oscillator'. Luckily for us and the purposes of this tutorial, 99% of all microcontrollers have built-in circuitry so that by attaching a cheap 'crystal' to the two input pins, the internal drivers will drive the crystal, create an oscillator, and the micro will have a good clock source. Please forgive us and all the other technical documents that incorrectly use 'oscillator' and 'crystal' interchangeably.
Some negatives of crystals:
Crystals are a bit expensive. $0.25 compared to $0.10 of a resonator.
They cannot be made as small as a resonator (crystals take up more PCB area).
Crystals require 'load capacitors'. Load capacitors start the crystal oscillating. Without the load caps, your crystal may function today, but someday it may not. Load caps are cheap, but they take more room on the PCB.
External Resonator -
Resonators fall in between the internal RC and a crystal.
A resonator is a piece of ceramic that is manufactured in such a way to oscillate at a given frequency. Unfortunately this process is difficult to do well. Resonators have a standard tolerance of +/-0.5%. So resonators are 10 times more accurate than the internal oscillator but they are still a bit 'loose' compared to crystals.
Resonators tend to be cheaper than crystals. Resonators tend to be lower frequency than crystals. Resonators are cool because they have the 'load caps' built into the 3-pin device! Resonators can be made *very small* and can minimize your PCB area.
So pick your poison. For many applications the internal oscillator is just fine! But if you're trying to do serial communication, 5% is usually too poor (serial tolerance is 1-2%). I've used crystals for most of my projects. But for the really small devices, I've used a resonator. Anything that deals with digital RF signals requires some really tight tolerance crystals. Any oscillator will fluctuate a bit over time (this is called 'aging') and any clock will vary with temperature.
As mentioned earlier, the ATmega168 ships configured with an internal 1MHz osc. But we can push it faster - and better! Let's setup the ATmega168 to run at 16MHz with an external crystal.
What are some of the side-effects of running the ATmega168 at this higher frequency? You will not be able to run the IC at this higher freq at lower voltages (such as 3.3V or 2.8V). Since we are dealing with a 5V supply, this is not a deal breaker. At 20MHz the micro will consume more power than at 1MHz. These are all things to consider when developing your own system.
How fast can I push it?
The max speed for the ATmega168 is 20MHz or 20MIPS! That's blindingly fast!
Get your 16MHz crystal out and find pins PB6/7.
Plug the crystal legs into these two pins and connect these pins to ground through two 22pF caps.
This completes the needed hardware, now we need to tell the ATmega168 to use the external crystal.
Fuse Bits -
This was one of the wildest, hardest thing to get used to with AVRs. The fuse bits are a very low-level configuration system. By setting or clearing these bits you can completely change how the AVR functions. I was a PIC guy for many years and PIC configuration bits were easy. You just clicked on a nice Windows GUI or programmed the bits directly into your C code. No fuss. AVRs are very different and you can literally break your AVR if you program the fuse bits willy-nilly.
There are two bytes on the ATmega168 that make up the 'fuse bits'. If you haven't already, download the full ATmega168 datasheet (currently it's 376 pages long!) and save it to your desktop. If you've never read a datasheet, don't worry! You don't need to know all 376 pages, you just need to know how to absorb information from it - and that's not trivial!
Let's do a search for 'fuse bits'. We get directed towards the 'Clock Sources' section. What a coincidence! (Be sure to have the book marks or section bar open so that you can see the different sections of the datasheet.) There are so many options for clock sources into the ATmega168. Let's start with tweaking the internal oscillator from 1MHz to 8MHz.
From page 34 (section 8.6): "By default, the Internal RC Oscillator provides an approximate 8.0 MHz clock. Though voltage and temperature dependent, this clock can be very accurately calibrated by the user. The device is shipped with the CKDIV8 Fuse programmed. See “System Clock Prescaler” on page 37 for more details."
So to get the internal oscillator to run faster, we need to change the CKDIV8 fuse bit.
Ahah! Here we see how the ATmega168 worked right out of the box. Atmel ships these to use the 'Calibrated Internal RC Oscillator' (8MHz) with the 'Divide clock by 8' set as well (1MHz). Very good. Now we just need to change the CKDIV8 bit.
Default Low Fuse Byte : 0b.0110.0010
New Low Fuse Byte : 0b.1110.0010
Using these new fuse bits, the ATmega168 should start running at 8MHz internal osc and we should see the LED blink 8 times as fast! There is a couple ways to do this, but the way that I've found to be most straight forward is a bit command line intense. Open up a command prompt and type 'avrdude'. You should get a mass of help text. If you're using a PG1 (serial) or PG2 (parallel) programmer, you'll need to select the right string:
To read the ATmega168 fuses:
PG1 (serial):
avrdude -p m168 -P COM1 -c ponyser -U lfuse:r:-:h -U hfuse:r:-:h
PG2 (parallel):
avrdude -p m168 -P lpt1 -c stk200 -U lfuse:r:-:h -U hfuse:r:-:h
Again, I am going to assume you're using the PG2, but you can modify the strings to work with a serial programmer. This basic string should cause avrdude to report back the default fuses for the ATmega168 - High fuse = 0xDF, Low fuse = 0x62
How do I form a new fuse byte? Keep searching for 'fuse bits' until you hit page 288. This shows the two fuse bytes (high and low) and their default values. All you need to do is change the lower fuse byte from 0x62 (0b.0110.0010) to 0xE2 (0b.1110.0010). Now we splice this into the previous read string and switch from read to write.
Internal 8MHz:
avrdude -p m168 -P lpt1 -c stk200 -U lfuse:w:0xE2:m
Run this string at the command prompt and wamm-o, your AVR should be running at 8MHz. I have had a few instances where avrdude reports some errors reading the fuses and prompts if I want to 'recover' the fuse settings or some such error. I'm not sure what the error is. You can say yes/no (doesn't matter), and then send the same string. The second try should successfully set the fuses. All right, the LED should be blinking like crazy, now let's take it up one more notch to 16MHz.
Notice how I don't have 22pF load caps on my 16MHz crystal? Bad engineer! Bad!
What are 22pF used for? These small capacitors help 'load' the crystal allowing it to oscillate. Without them, the crystal may not start oscillating - hence, your system might not run. This rarely happens, but in a full blown product, this would be disastrous! It's ok to skip them for bread boarding purposes, but good engineering practices require them.
You will need to have the 16MHz crystal attached to the oscillator pins as shown in the last schematic above. Go back to the 'Clock Sources' category in the datasheet and do a bit of research for the external crystal oscillator option. I'll give you a hint, it's going to look something like this:
CKDIV8 = 1
CKOUT = 1
SUT1 = 1
SUT0 = 0
CKSEL3 = 0
CKSEL2 = 1
CKSEL1 = 1
CKSEL0 = 0
16MHz external osc:
avrdude -p m168 -P lpt1 -c stk200 -U lfuse:w:0xE6:m
Once you get this programmed, the ATmega168 should be utilizing the external 16MHz oscillator blinking the LED super-fast. If not, check your load capacitors and the xtal connections. The ATmega168 has a maximum speed of 20MHz (20 MIPS!). Try overclocking your micro some day with a 30MHz or 40MHz crystal. More than likely it will work just fine, but you'd never want to design a real system around an out-of-spec clock speed.
Homework time. You will need to learn how to use your multimeter to measure current consumption. Because current is measured in series (voltage is measured in parallel) you will need to find a spot on your breadboard where all the current being used by your bread board can be interrupted and measured. Measure the current draw:
When the ATmega168 is in reset = ?
When the ATmega168 is running with 1MHz internal osc = ?
8MHz internal osc = ?
16MHz external osc = ?
A great resource that we use religiously is the AVR fuse calculator:
http://palmavr.sourceforge.net/cgi-bin/fc.cgi
Use it to double check your fuse settings and avoid permanently killing your AVR.
During each one of these experiments, do a quick temperature test of your voltage regulator. In general, the regulator should be cool enough to touch. If it's red hot (be careful!) you should turn off your breadboard and check for shorts.
Why do regulators heat up? We are using a very basic linear regulator. This type of regulator inputs a higher voltage (in my case 9V) and outputs a lower voltage (5V). The difference in voltage is expelled as heat through the metal tab. This heat is measured in wasted power or Watts. If your input is 9V, output is 5V, and your 5V system uses 50mA:
(9 - 5) * 0.050 = 0.2W or 200mW
200mW will cause the regulator to heat up a bit. How about an amp?
(9 - 5) * 1.000 = 4W!
That's some serious heat! The regulator will be very hot and may be permanently damaged if it's allowed to run at super-high temperatures for extended periods of time.
You may have noticed, by lowering the input voltage, we can reduce the amount of heat expelled. Why not just input 5V and call it a day? These cheap linear voltage regulators require something called 'drop-out voltage'. This is a very non-technical term for the extra voltage the regulator needs to output the required voltage. Anything below this voltage and the regulator will 'drop-out' the output voltage below the rated voltage. For LM7805 it's a good rule of thumb to have 1.5V of overhead meaning you need to input at least 6.5V to get 5V on the output. If you input less than 6.5V (4 AA batteries for instance), the 5V output is not guaranteed. Each voltage regulator is different so check the datasheet for the part in your hand! Some v-regs are specifically designed to have low drop out voltage. Some smaller v-regs have as low as 50mV! Our standard 3.3V regulator requires a minimum of 3.35V to output a solid 3.3V.
Many regulators have an internal shutdown feature that prevent the regulator from destroying itself if there is a short on the output. If you flip the power switch on your breadboard and the LED doesn't turn on, odds are your voltage regulator is trying so hard to output enough current (because you've hooked up a component backwards or worse) that the regulator shuts down and the LED has no power to illuminate. If this is the case, shut down your breadboard asap.
In general, voltage regulators will run warm. This is ok. It you ever smell something odd or you can feel a heat wave from your breadboard, just shut things down and take a second look.
You can get all the parts for this lecture here.
From now on we will run things with an external 16MHz crystal. Vary as your project needs it.

Beginning Embedded Electronics - 2

2009-05-15T03:29:00.000-07:00

Lecture 2 - How to Get Code Onto a Microcontroller
You can get all the parts for this lecture here. We also highly recommend that you get a multimeter with a 'continuity' setting. A good quality multimeter with this setting goes for ~$60 and as high as $300 for a really spectacular one. We like our $60 cheapo.
Sorry for the confusion. When these tutorials were written and photographed, we used the ATmega8. We now carry the newer ATmega168. You will find all ATmega168 information in the following pages, but the pictures will show an ATmega8.
I'm assuming you've got your 5V supply tested and working. Next, we need to insert the ATmega168 into the breadboard and connect up power and ground.
ATmega8 (works the same with ATmega168) straddling the middle row of the breadboard
You will need to slightly bend in the legs of the DIP (dual inline package) to get the ATmega168 to straddle the breadboard center. Be careful! Do not bend the pins too far inward. The pins of the ATmega168 should insert into the inner two most rows on the breadboard. I find it best to to insert one side and then slightly push the IC sideways until the other side of pins can insert into the opposite row on the breadboard. Confusing, I know.
Note: The 5V 'rail' is the horizontal row of holes next to the red line. You should have a wire connecting your 5V power regulator circuit to one hole on the 5V rail. This will energize all the holes next to the red line with 5V. This is true about the blue line as well. All the horizontal holes next to the blue line are connected together. One of these holes should be connected to the ground pin on your voltage regulator, and to the ground connection of your wall wart. You can connect the VCC pins on the ATmega168 to any holes along the 5V rail, and you connect the GND pins on the ATmega168 to any hole along the blue GND rail.
Oh, hey! If no one ever told you, there is a really simple way to figure out where pin 1 is on an IC. The manufacturer of anything polarized (tantalum caps, electrolytic caps, LEDs, ICs, etc) will always put some sort of marking on the device to indicate the how the device is supposed to be oriented. For ICs, there is a small dimple on one end of the IC. The blue arrow in the picture is pointing to this dimple. The orange arrow points at pin 1, and the blue labels show how the pin numbers increase.
Pin labeling on an IC
Counting from the dimple, pin 1 is on the left and increases down the left side of the IC. The pin numbers jump to the right side row of pins and count up. See image from the ATmega168 datasheet below.
The ATmega168 should be in the breadboard, pin 7 (VCC) and pin 20 (AVCC) should be connected to your 5V rail and pins 8 and 22 (GND) should be connected to GND on your bread board. If you turn your power circuit on, the ATmega168 is now running, but it has nothing to run!
Actually this is not wholly true - there is one more connection that needs to be made before the ATmega168 starts running code. The RESET pin on the ATmega168 needs to be connected to VCC. You can either wire the RESET pin directly to 5V or you can 'tie it high' by connecting the RESET pin to VCC through a resistor. This will allow you to add a momentary reset button. What's this? The reset line on the ATmega168 is exactly what it sounds like - it resets the micro just like the reset works on your computer. If you look at the ATmega168 datasheet you'll see the RESET label is written with a line above it. This is nomenclature that indicates the reset pin is active low. What is 'active low'? The RESET pin is an input. A low level on this pin will put the micro into reset - i.e. the pin is activated with a low input, aka 'active low'. So unless you want your ATmega168 to stay in reset, you'll need to pull this pin high.
Now you need a reset button. A momentary switch is a switch that is activated (or closed) while you're touching it and open when you release the button. These are often called 'tactile switches' because they 'click' when you depress them giving the person pressing the button some 'tactile' feedback.
This is what the schematic part looks like. Notice pins 1 and 2 are connected together. 3 and 4 are connected together. And when you press 'de button, it temporarily connects 1/2+3/4 together.
Notice this button has five legs. If your button has five legs, just ignore the middle leg - it's not connected to anything and can be clipped off.
To test this button, whip out the trusty multimeter and set it to the continuity setting. This is the setting on nicer, mid-grade multimeters that is crucial to troubleshooting and experimenting. Touch the probes together - you should hear a tone indicating that there is continuity or a (nearly) zero resistance path between the probes. Insert the button into the breadboard and probe the two pins on one side of the button. If you picked pins 1/2 or 3/4 you should hear a tone. These pins are permanently connected inside switch. If you picked pins 1/3 or 2/4, you won't hear a noise - but hit the button. By hitting the button you will make an electrical connection between all four pins - and you should hear the tone! This means you have electrical continuity.
The schematic shows pins 1 and 2 of the reset switch connected together (connected to ground) and pins 3/4 connected together (connected to !RESET) . In practice, you just need the switch to work. Play with your multimeter and find two pins that don't make noise when the button is not touched, and do make noise when the button is depressed. Use these two pins.
The schematic shown above is what we're going for. The 10K resistor 'pulls' the reset pin high during normal activity. By pulling the reset pin high, the ATmega168 runs normally. When you push the reset switch (S2), the reset pin sees a continuous connection to ground. Since the resistance through the depressed switch is nearly zero, it wins (compared to the resistance of the 10K resistor!) and the reset pin is pulled low, RESET is activated and the ATmega168 goes into reset. Release the button and the reset pin is pulled high again and the ATmega168 comes out of reset. Nifty!
ATmega168 pinout
See the dimple from the ATmega168 datasheet? Looking at the top of the IC (legs down), with the dimple to the top, pin numbers increase starting from 1 in the top left corner. This is how every IC pin is number. However, the orientation marking varies a bit between manufacturers and between packaging types. Look for a non-congruent marking like a dimple, small dot, white arrow, a notched corner - anything that makes that area of the chip different from the other parts of the chip probably indicates pin 1. When in doubt, check the datasheet.
Reset wired next to a ATmega8 (same applies for the ATmega168)
Learn how to use the the continuity setting on your multimeter. It will be vital to troubleshooting down the road!
Each microcontroller manufacturer has a different method to get code in the flash memory of the micro. In the past few years there has been emphasis placed on ISP or "in system programming". ISP allows you to program the IC without having to disconnect the microcontroller from the application. This is not trivial! History was much more painful. Atmel has designed a relatively straight forward method that requires the control of a few pins (6 total). Because of this simple interface, the hardware programmer that is required to connect your computer to this SPI interface is very straight forward (cheap!) as well.
The red stripe indicates the location of Pin 1
Remember how we identified pin1 on the IC from the dimple? Well connectors also need polarization so that we don't reverse the orientation of the connector and fry things. Unfortunately the way connectors are numbered is opposite that of ICs. In the picture of the ISP connector, you see the red stripe indicating pin 1. An IC counts sequentially down one side. Connectors on the other hand, increase pin numbers, back and forth, as you work your way down the connector.
The programming chain looks something like this:
There is a free C compiler called AVR-GCC. User writes code in C and then compiles that code into HEX files
AVR-GCC can be installed on the Windows platform with an easy WinAVR install program
The user gets this HEX code onto an AVR via the ISP pins
Both a serial port programmer and a parallel port programmere have been designed to connect the computer port to the AVR ISP pins
The computer runs a command line program to transfer the HEX file from the computer, to the serial or parallel port, and out to the AVR ISP pins
The micro runs the machine code (*.HEX files) once powered or reset
What's a C compiler? This is a program that inputs a program written in the C language and outputs a HEX file. We prefer to program in C because it is easier for us than assembly and more flexible than BASIC.
What's a HEX file? This is a file that contains various hexidecimal characters. These hex 'codes' represent machine instructions that the ATmega168 understand. This file is what gets sent down to the programmer, and the programmer loads these machine instructions onto the ATmega168.
Before we can get too crazy, download and install WinAVR on the computer that you will be doing your code development on. If this link goes out of date, a google search should take you straight to it. The windows install should be fairly straight forward - follow all the defaults. WinAVR contains a version of the GCC compiler and various other tools including avrdude and Programmer's Notepad. avrdude is a simple command line program that takes a HEX file and sends it to the serial or parallel port for programming onto an Atmel microcontroller.
Working backwards up this list, I'll provide you with an example 'Hello World' HEX file that will prove that everything is working correctly on your micro. With any micro controller board, the first trick is always to get an LED to blink. This is the 'Hello World' of embedded systems. Guess what blink_1MHz.hex does?
With the blink hex file in hand, you now need to get it onto the micro. You will need to connect the AVR-PG1 (or the AVR-PG2) to the ATmega168. The easiest way to do this is with 9 wires running from your breadboard to the 10-pin connector on the ISP connector on the AVR-PG1/PG2.
Jamming wires into the ISP connector is not a good long-term solution but for the sake of getting the LED to blink, it'll do. I've cut short wires and stripped both ends. One stripped end is inserted into the end of the black programming connector, the other end is inserted into the breadboard.
The AVR-PG2 parallel programmer wired into the ATmega168. I've also wired up two 0.1uF caps. These decoupling caps are placed near the VCC and GND pins on the ATmega168 to help reduce noise into the IC. You may think you have a straight DC 5V but not really - these 0.1uF caps help reduce ripple on the 5V line. Yes, the ATmega168 will probably run without them but they're good to have installed.
AVR ISP Note: You really do have to wire all 4 GND pins. You cannot wire just one of the GND pins on the ISP connector.
Additionally we need an LED to control. This can be tied to any GPIO pin. PC0 looks like a good spot.
The resistor/LED order does not matter - just remember (from Tutorial 1) that you must have the resistor! The GPIO pin doesn't actually matter. blink_1MHz.hex will toggle all the pins on all ports so you can hook the resistor to any pin. As you add more peripheral hardware you will want to dedicate some pins for alternate use (such as TX and RX pins for serial communication).
You're getting closer! Time to program the chip!
Once WinAVR is installed, you should have a few new icons on your desktop. Programmers Notepad is a nice code editor and highlighter.
What's a code editor/highlighter? When programming, you will need a text editor on your computer so that you can create (type) code. Once you've created this 'code' on your computer (inside the code editor) you will pass this code to the compiler (you will click a button that runs the compiler with the C file you've typed) and the compiler will create a HEX file (assuming there are no problems or typos in your code). The highlighter? When creating code, it's often nice to have various parts of your program color coded so that you can tell a common things like for( ) and #define. This highlighting helps a lot when programming.
Use whichever text tool you like. Notepad will work, but is pretty rudimentary. I also likeJFE from my PIC days. Both have a 'tools' option which is great but JFE is better in my opinion because it lists the C functions that you can double click on and navigate to. If there is a way to do a similar trick in Programmer's Notepad 2, please let me know! Because Programmers Notepad v2 (aka PN2) comes with the WinAVR installation, we'll use it!
AVR-GCC is extremely powerful, very complex, and difficult to use initially. I am used to passing a *.c file to a PIC compiler (CC5x) and getting a HEX file back out. No fuss, no mess. Believe you me, the pain of getting AVR-GCC up and running is worth it. AVR-GCC is a truly nice compiler, and it's free. I've included a stock Makefile and blink_1MHz.c file inblink_1MHz.zip to get you started. I am by no means a Linux or make type of person. All you need to know is that when you type 'make' at the command prompt, the compiler is going to look for a file called 'Makefile' (no file extension!) and use that file to direct how to compile your C file.
These are the only two files you should need to get blink to compile. Open up blink_1MHz.c in programmer's notepad and click on Tools->Make All. This is the same as typing 'make all' from the command prompt from what ever directory you saved these two files. For example
C:\Code\Blink>make all
should compile your code as well. It's just a bit easier to do this through the Programmer's Notepad interface rather than toggling back and forth to the Command Prompt window. Once you have successfully compiled the C file into a HEX file, you now need to get that hex file onto the AVR. It's finally time to power up your system! The cheap AVR programmers require the target (that's your breadboard) to provide power to the programmer (that's the AVR-PG1 or PG2). Power up your bread board - you should see the power LED come on. From here on out, I will assume you're using the AVR-PG2 parallel port programmer.
There is only two spots in the makefile that you should be concerned about at this time. These two spots are located under the programming options section. This makefile is huge, but scroll down to the Programming Options (avrdude) section. Now put a '#' in front of lines you want to comment out.
If you're using the AVR-PG1 (serial port programmer) you edit like this:
#AVRDUDE_PROGRAMMER = stk200
AVRDUDE_PROGRAMMER = ponyser

# com1 = serial port. Use lpt1 to connect to parallel port.
#AVRDUDE_PORT = lpt1
AVRDUDE_PORT = COM1
If you're using the AVR-PG2 (parallel port programmer) you edit like this:
AVRDUDE_PROGRAMMER = stk200
#AVRDUDE_PROGRAMMER = ponyser

# com1 = serial port. Use lpt1 to connect to parallel port.
AVRDUDE_PORT = lpt1
#AVRDUDE_PORT = COM1
Of course the port numbers depend on your specific computer but once you get things working, you'll be set for life. Assuming you've edited and saved your makefile, go back to PN2. With your breadboard powered, click Tools->Program. This will send the command 'make program' to the command prompt. If everything is setup correctly, you should have successfully loaded blink_1MHz.hex onto your target ATmega168 and your LED should be blinking.
If you get an error :
can't open device "giveio"
Then read this page. Basically you need to copy the giveio.sys file from C:\WinAVR/bin to the C:\Windows directory, then type install_giveio.bat at the command prompt.
Typical Problems:
If you still are not able to program the AVR - this is where 99% of first time users end up. Dig in and troubleshoot.
Are the ISP connections correct? It's easy to get the ISP connector backwards. Take a look at the photos above.
Is there a loose wire? Pull out the multimeter and check that you've got 5V being delivered to the VCC and GND pins on the ATmega168. Do the wires going into the ISP connector have a good solid connection?
Do you have your ATmega168 connected to both power and ground?
Is your 5V supply outputting 5V?
Do you have the right COM port or LPT port selected in your makefile?
There is a multitude of things to check. It's hard! I know. But once you get things correctly set up, and that LED blinks - it will feel fantastic!
Ok - I'm going to assume that you got the code correctly loaded onto the AVR and that the LED is blinking. Congratulations! You are now well on your way to a whole world of pain! Once you get one thing working, it's hard to stop! GPS, datalogging, RF, PCB layout - it's all just a couple hops away.
You can get all the parts for this lecture here.
Here are some additional resources for AVR programming:
http://www.piconomic.co.za/avr.php
http://www.salvitti.it/geo/sequencer/dev_tools/tutorial/GNU_C_Tutorial.html
http://palmavr.sourceforge.net/cgi-bin/fc.cgi