an esq summer camp project - july 2001light. there are ir lasers and ir light emitting diodes (ir...

An ESQ Summer Camp Project - July 2001An ESQ Summer Camp Project - July 2001An ESQ Summer Camp Project - July 2001An ESQ Summer Camp Project - July 2001

http://www.esq.uwaterloo.ca

COM DEV SPACE - Light-Wave Communicator Project for ESQ1

INTRODUCTION............................................... 2

USING LIGHT TO TRANSMIT AND RECEIVESIGNALS.......................................................... 3

PROPERTIES OF LIGHT............................................................................................................................... 3VISIBLE LIGHT VS. INFRARED LIGHT ....................................................................................................... 4AM VS. FM TRANSMISSION..................................................................................................................... 4

LIGHT TRANSMITTERS AND DETECTORS.......... 7MAKING INFRARED LIGHT ......................................................................................................................... 7DETECTING INFRARED LIGHT.................................................................................................................... 7INTERFERENCE ........................................................................................................................................... 8

THE TRANSMITTER CIRCUIT .......................... 10TRANSMITTER CIRCUIT DESCRIPTION .................................................................................................... 10PARTS LIST AND DIAGRAM ...................................................................................................................... 11ASSEMBLY INSTRUCTIONS ...................................................................................................................... 12

THE RECEIVER CIRCUIT................................. 14RECEIVER CIRCUIT DESCRIPTION........................................................................................................... 14PARTS LIST AND DIAGRAM ...................................................................................................................... 15ASSEMBLY INSTRUCTIONS ...................................................................................................................... 16

USING THE COMMUNICATOR ......................... 17

THINGS TO TRY ............................................. 18EXTENDING THE RANGE .......................................................................................................................... 18REDUCING INTERFERENCE ...................................................................................................................... 19SOUND QUALITY...................................................................................................................................... 20TRANSMISSION AND REFLECTION MEDIA ............................................................................................. 20OTHER SOURCES OF IR .......................................................................................................................... 20

APPENDIX A - THE RESISTOR COLOR CODE ... 21

APPENDIX B - LIST OF SUPPLIERS ................ 23

http://www.comdev.ca


IntroductionThe purpose of this project is to teach you something about infraredlight and its use in communications. You will build a light-wavetransmitter and receiver that is capable of sending and receiving voice,music or even data over an invisible beam of light. The uses that youwill find for it are limited only by your imagination! This paper is foryou to take home and read at your own convenience. It explains indetail why and how this project works. It provides you with enoughinformation to explore infrared light communications and applicationsand learn more on your own.

Although this paper describes the project in detail, your instructors willprovide additional information and help in building the circuit. In theprocess of learning about light-wave communication, we hope that youwill enjoy building, tinkering with and using your circuits. Building anelectronic circuit will teach you about electronic components,component identification, proper handling, soldering and allow you topractice your mechanical building skills.

CAUTION: Please read these precautions before starting your project.

The light-wave communicator described here is for experimentationand demonstration purposes only. Do not attempt to use this circuit tobuild audio transmission equipment for your own use or for anybodyelse. The sounds from the speaker can be loud. Protect your hearing!Don't place your ears close to the speaker! Never attempt to replacethe speaker with a headphone or earphone set. Place the transmitterand receiver at least 5 feet away from each other while testing thealignment and sound levels. Do not attempt to increase the powersupply voltage without reading this paper completely.

But don't be afraid to experiment safely and try out your ideas!Remember, the most important requirement for learning is having fun!

Ian A D'Souza


Using Light to Transmit and Receive Signals

Properties of lightLight is an electromagnetic (EM) wave. Other EM waves that you arefamiliar with are radio waves, microwaves, x-rays and gamma rays.The only difference between all these types of waves is that they aredifferent frequencies of EM waves. Most communication equipmentuses some type of EM waves because they are quite easy to generateand manipulate and they travel at the speed of light - 300,000,000m/s. That certainly minimizes the time delay between sending asignal and receiving it!

Some other properties of EM waves are also very useful. Radio waves,for example, can come right through the walls of your house so thatyour stereo and CD player as well as your television can receive them.

Radio signals are severely reflected by structures that are goodconductors of electricity and can be absorbed by those that are verythick or lossy (absorbing). If you lived in steel cage, it would bedifficult to receive these signals as they would be reflected instead ofpenetrating the building. Submarines must surface before they cantransmit or receive radio waves (or they must launch an antenna tothe surface). This is because sea water is an excellent conductor ofelectricity. If you lived deep inside the earth, it would again be hard toreceive signals as the earth can absorb the signal. Some materialsabsorb EM waves more than others for a particular frequency of wave.For communications, you need to make sure that your transmittedwaves are not absorbed.

Because light is an EM wave, it behaves in much the same way asradio waves. Light is reflected by conductive materials such as metal.. On the other hand light is absorbed in non-metallic materials tovarying degrees depending on the material, window glass does notconduct well at visible light frequencies - it lets visible light passthrough because it does not absorb visible light too much. In fact, agood picture to keep in mind is that ALL materials reflect, transmit andabsorb EM waves (like light) in varying amounts. Think of all thethings that light can penetrate and compare with what radio waves,microwaves or x rays do.


Visible light vs. infrared lightIn the same way that you can tune in to different radio stationsbecause they are on different frequencies, light too comes in differentfrequencies. To people, different frequencies of light are experiencedas different colors, in fact, light is the only electromagnetic wave thatwe can detect directly with our senses. The lowest frequency of lightthat we can see is red light. The highest frequency of light that wecan see is violet in color. Red and violet are the ends of an infinite'spectrum' of colors that we can see. This spectrum is referred to asthe visible light spectrum. Roughly, the colors are (lowest frequencyto highest): the reds, the oranges, the yellows, the greens the blues,the indigos and the violets.

When the frequency of the light is too high or too low, our senses can'tdetect it any more. If the light is too high in frequency, we say that itis ultraviolet (UV), meaning higher in frequency than the color violet.If the light is too low in frequency to see, we say that the light isinfrared (IR), meaning lower in frequency than the color red.

In this project we will be working with IR light. Most sources of light -e.g. the light bulbs in your house - emit light in both the visible andinvisible spectrum. That is, your house light bulbs includingfluorescent bulbs emit infrared as well as visible light. You only seethe visible part of course. Sunlight also contains a large portion of IRlight. Warm objects also emit IR light. As a hot object (like a fireplacelog) cools, it goes from a bright color to orange to red until it looks likeit has stopped giving off light. But it continues to give off light in theinfrared. Our bodies, being at 37°C (98.6°F) also give off infraredlight. There are IR lasers and IR Light Emitting Diodes (IR LED's) thatare designed to emit infrared light.

Our project will be using IR LED's to transmit an invisible signal to adetector capable of detecting IR light. We will use electronics toconvert sound waves or audio signals into light waves, transmit thelight and then convert the received light back to sound.

AM vs. FM transmissionIn this project we have chosen to use infrared light. How do we usethe light to send a signal?

To understand what is happening, imagine that we are using visiblelight - say red light, instead. How would you send a signal to your


friend? Perhaps the first question that pops into your head is "whatam I signaling about?"

Suppose that you just want to say "hello". You could, in advance,decide that when the light is on, it means "hello". If it is off, …well… itjust means that it's off.

So you turn your light on and your friend sees it. She understandsthat it means hello. Perhaps she has a similar light and sends a "hello"back. Great! You have sent a signal using light!

Of course, just being able to say "hello" is not very practical. What ifyou want to send a whole sentence? You could invent a code for eachletter of the alphabet, e.g. three short flashes means 'S' and threelong flashes means 'O' etc. Then you could each learn Morse code andsend messages. Better... but still not very efficient or very good. Youcouldn't send actual music or sounds, for example.

If instead of turning your light just on and off, what if you could varythe brightness continuously from off to bright? Then each nuance ofbrightness or dimness could stand for something. You could actuallysend sound using this idea, here's how it would work: To send thenote 'A' on the musical scale, you would make your light go from dimto bright 440 times each second. That is because the note 'A' in astandard concert tuning corresponds to a vibration of 440 times persecond, or 440 Hertz. If you wanted to send a loud 'A' note you wouldmake your light go from very dim to very bright 440 times a second.A soft 'A' would go from medium dim to medium bright, 440 times asecond. In general, the range of the change in brightness correspondsto the loudness, while the number of changes per second through thedim-bright range corresponds to the frequency of the sound. If thelight remains steady at medium brightness all the time, it means thatno signal is being sent.

Hmmm…Great! But how would you change the brightness that fast?And how would the person looking at the light get the sound from thisinformation? - assuming that she could even notice the slightdifferences in brightness with any accuracy! Simple…. Our circuit willdo that!

When we transmit the sounds, we first convert the sound to anelectrical signal which we will use to make the light brighter ordimmer. How do we get an electrical signal from sound? We do thisusing a sound to voltage converter: a microphone! If we already have


a converted signal, say from a CD player output jack, we simplyconnect the output to our circuit since it is already in 'electrical voltageform'!

Then at the receiver end, we detect the light with a sensitive lightdetector that generates a voltage proportional to the brightness of thelight… the brighter the light, the greater the voltage. This voltage isused to operate a speaker. The fluctuating speaker voltage willreproduce the sounds that are sent.

This method of encoding the information onto the transmitted beam iscalled amplitude modulation (AM). Modulation is the act of encodingthe data to be transmitted onto a carrier medium. In this case ourcarrier is IR light and our modulation method is to vary its brightness.The extraction of information from a modulated carrier is called de-modulation or detection. The variation in brightness (modulation) isreceived by our detector, an IR photodiode, which converts thebrightness fluctuations into a voltage fluctuation.

Our transmitter and receiver will be AM devices that use light. In asimilar way, your home radio can detect AM radio waves sent by theradio station. The station uses sound to modulate radio waves insteadof light waves using very similar circuit techniques to what we will beusing.


Light Transmitters and Detectors

Making infrared lightThe sun, indoor light bulbs and fluorescent lighting as well as warmobjects are some sources of readily available infrared light. For thisproject we will be using infrared light emitting diodes or LED's in thetransmitter circuit.

These semiconductor devices are designed to emit light at awavelength of about 900 nanometers. That wavelength of lightcorresponds to a color that is not detectable by human vision. ManyTV or stereo remote controls make use of IR LED's to send an invisiblebeam of modulated signals to a detector inside the TV or stereo. Thecircuitry of the detector de-modulates the signal and sends the code toa built in computer or decoder circuit to act on the command sent.

IR LED's are semiconductors and should be handled with care. Do notexpose these to extremes of temperature. When soldering them toyour circuit, work quickly and use a heat sink clip if you are unsure ofyour soldering abilities.

The LED's you will be using have two pins that are notinterchangeable. They must be wired into the circuit with the correctpolarity.

Detecting infrared lightThe receiver circuit uses an infrared photodiode, which is a lightsensitive semiconductor detector.

The particular device that we will be using incorporates a built-invisible-light optical filter. This is because photodiodes can detectvisible light as well as IR and we will need to minimize visible lightgetting to the sensitive area of the photodiode. The photodiode caselooks black and you would think that light could not get inside. This isjust the optical filter that blocks visible light, but transmits infraredlight through the case of the photodiode. The detection area of thephotodiode is about 7 mm2.

The pins of the photodiode are not interchangeable, they must bewired into the circuit with the correct polarity.


InterferenceBecause light bulbs produce infrared light as well as visible light, thiscomponent of IR will get through the optical filter to the photodiodesensitive area. In your homes, the light bulbs work on an alternatingvoltage that cycles 'negative' to 'off' to 'positive' to 'off' at 120 timesper second. Thus, the light bulbs in your home are actually switchingon and off at 120 times per second. You don't see this because (a) itis too fast and (b) the bulb does not have time to cool down too muchduring the switching. Nevertheless, there is enough amplitudemodulation (AM) of the brightness from this switching that yourphotodiode will pick up the 120 Hz 'hum' from these 'flashing bulbs'infrared signal.

There is not much one can do about that other than shielding thephotodiode in a tube made of say cardboard to protect it from theoverhead lights while pointing it at the IR LED's from the transmitter.One could also turn the lights off.

As the transmitter is moved away from the detector, the light from theLED's is spread out over a larger area. The density of light getting tothe detector will drop and the signal will get weaker. At somedistance, the intensity of the light from the LED's will be equal to thesignal from the stray sources of light (e.g. the light bulbs overhead)and at greater distances, the stray noise will dominate. At that point,the signal will fade into the noise.

Because the LED's tend to produce light in a forward cone with about a20 degree cone angle, you will need to align the transmitter andreceiver more carefully as you move them further apart. One way ofincreasing the distance over which the units will operate is to uselenses to focus the light. Normally, in a room with subdued light, thedevice will transmit well over a distance of about 30 feet. If lensesare used, the operating range can be extended to hundreds of feet atnight. This is described in more detail at the end of this paper.

Since this is basically a line-of-sight transmitter/receiver, there is littlechance that the signal will interfere with other devices or that thesignal will be detected by other devices. Such transmitters aresometimes used for security reasons.

The receiver incorporates a sensitive amplifier. The amplifier has ahigh gain and will amplify even small signals at the input. Touching


the input leads or pins can cause the pickup of stray EM signalscoupled through your body into the amplifier. You can get it to humby touching certain pins at the input.


The Transmitter Circuit

Transmitter circuit descriptionThe transmitter circuit is shown in Figure A. The signal to be sent iscoupled into the circuit at C1. The signal may be from a radio ormicrophone plugged into the jack or any other source. This signal iscoupled via capacitor C1 into the input of a integrated circuit, the 741operational amplifier. The gain of the amplifier is set to a value ofabout 120 by resistors R1 and R4. Resistors R2 and R3 maintain theinput DC bias point of the amplifier. The output of this amplifier at pin6 is fed via C2 to transistor circuit Q1, R5 and R6 which are wired as acurrent amplifier. The transistor circuit used is called an emitter-follower and it provides the drive current for the infrared light emittingdiodes D1 and D3. The 33 ohm, 1/2 watt resistor R7 limits themaximum current through the LED's.

Transmitter Schematic


Transmitter Assembly

Parts list and diagramC1 0.1 uF capacitorC2 1.0 uF, 16V, electrolytic capacitorD1,3 LD271, 12 mW infrared LEDR1 8k2, 1/4 watt resistorR4 1M, 1/4 watt resistor


R2,3,5,6 5k6, 1/4 watt resistorR7 33 ohm, 1/2 watt resistorU1 LM741 operational amplifierQ1 2N2222A npn transistor, TO18 case style

Assembly instructionsThis should be a straight forward assembly. Make sure that yoursoldering iron is clean and well tinned. The tip should appear shiny. Itis assumed that you have been instructed in the art of creating a goodsolder joint. Work neatly and quickly, minimizing heating of thecomponents. If you are unskilled at soldering, consider using heat-sink clips on the leads of the semiconductor components.

A good rule to follow is to assemble the heat sensitive componentslast. That is the semi-conductors like the transistor, integrated circuitand the light emitting diodes should be soldered in last. Reversing thiscould potentially expose these devices to excessive temperaturesduring the soldering of other components.

In this case, solder the resistors and capacitors first. Observepolarities on electrolytic (polarized) capacitors. Be sure to familiarizeyourself with the resistor color code to ensure that you have theresistors correctly in their places. If you have a socket for theintegrated circuit, it should also be soldered in at this time.

Next, solder in the transistor and LED's. Make certain that the leads(pins) are not interchanged - these components can be permanentlydamaged if power is applied to incorrectly installed semiconductors.The LED's pins should be bent so that they point off the edge of theboard prior to soldering. Use a pair of long nose pliers to bend thepins at right angles prior to assembly. The integrated circuit goes inlast (note if you have a socket, carefully press the chip into place -watch out for bent pins!) be certain to install the chip in the correctdirection. Pin 1 on integrated circuits is usually marked with a dot, ora cutout appears on one side to help you locate pin 1.

Install the battery clip.

Carefully inspect your solder connections for shorts. Remove anyaccidental shorts with a dull knife.

Double check that all component values and pin orientations arecorrect.


Apply power to the transmitter and check the following:

With a voltmeter, connect the common or ground lead of the meter tothe transmitter ground and measure the voltage at the junction of R5and R6. This reading should be about one-half of the power supplyvoltage of 9 volts, i.e. 4.5 V. Measure at the junction of R2 and R3,and again you should get approximately the same reading. Nowmeasure the voltage at the point where R7 connects to transistor Q1.This should be about 0.5V less than your previous measurement -about 4 volts. Don't worry about exact values, these are meant to beapproximately correct. If your values differ greatly, first check thatyour battery is 9 V, if it is, disconnect the battery immediately and re-check your work - soldering, component values etc. That's it, you'retransmitter is ready.


The Receiver Circuit

Receiver circuit descriptionThe light from the transmitter is received by the photodiode D2(SFH235). Note that this diode is biased with its cathode towards thepositive supply rail. The signal is coupled via C3 to the 741operational amplifier, which has a gain set near 1200 by R13, R11 andbias set by R10 and R12. The output of the 741 is coupled to theLM386 power amplifier, which is capable of driving a small speaker.Note that the power supply of the 741 is buffered, or de-coupled, fromthe power supply of the 386 by an RC filter consisting of R8 and C4.This is to keep voltage spikes, that can occur when the 386 isdelivering large currents to speaker, from disrupting the high-gain 741via any voltage drops that can be impressed on the bias of thephotodiode.

Receiver Schematic


Receiver Assembly

Parts list and diagramC3 0.1 uF capacitorC4,5,6 100 uF, 16V electrolytic capacitorC7 1.0 uF, 16V electrolytic capacitorD2 SFH-235 infrared photodiode with optical filterR9 220k, 1/4 watt resistorR8 220 ohm, 1/4 watt resistorR11 820 ohm, 1/4 watt resistorR13 1M, 1/4 watt resistorR10,12 5k6, 1/4 watt resistorU2 LM741 operational amplifier


U3 LM386 power amplifierSPK1 miniature 8-ohm speaker, 2.25 inch diameter

Assembly instructionsThis should be a straight forward assembly. Make sure that yoursoldering iron is clean and well tinned. The tip should appear shiny. Itis assumed that you have been instructed in the art of creating a goodsolder joint. Work neatly and quickly, minimizing heating of thecomponents. If you are unskilled at soldering, consider using heat-sink clips on the leads of the semiconductor components.

A good rule to follow is to assemble the heat sensitive componentslast. That is the semi-conductors like the integrated circuits and theinfrared photodiode should be soldered in last. Reversing this couldpotentially expose these devices to excessive temperatures during thesoldering of other components.

In this case, solder the resistors and capacitors first. Observepolarities on electrolytic (polarized) capacitors. Be sure to familiarizeyourself with the resistor color code to ensure that you have theresistors correctly in their places. If you have a socket for theintegrated circuit, it should also be soldered in at this time.

Next, solder in the photodiode. Make certain that the leads (pins) arenot interchanged - these components can be permanently damaged ifpower is applied to incorrectly installed semiconductors. Theintegrated circuits go in last (note if you have sockets, carefully pressthe chip into place - watch out for bent pins!) be certain to install theIC in the correct direction. Pin 1 on integrated circuits is usuallymarked with a dot, or a cutout appears on one side to help you locatepin 1.

Install the battery clip and speaker. You should glue the speaker(face-up) to the component side of the board, making sure that themetal casing does not make contact with any component.

Carefully inspect your solder connections for shorts. Remove anyaccidental shorts with a dull knife.

Check all component values and pin orientations. Notice that U2 andU3 have their pin 1 oriented on opposite sides as shown in theassembly diagram by the location of the notches in the IC.


Apply power to the receiver by connecting the battery. There will be adelay during a charging period for the capacitors - about 30 seconds.After this, a soft hiss will be heard in the speaker (if the room lightsare off). If the room lights are on, you will hear a hum correspondingto the 120 Hz of the lights. Place your hand over the photodiode andthis should reduce the hum (or turn off the lights!).

Using the CommunicatorTo use your light-wave communicator, follow these steps.

1. Place the transmitter and receiver about 3 feet apart.2. Turn on the receiver. Due to the large capacitance, there may

be delay of 30 seconds or so before you hear 'static' from thespeaker. If the room lights are on, you will also hear a hum.Turn off the room lights to stop the hum.

3. To activate the transmitter, first connect the battery. Thenconnect the audio plug to a radio or some other audio sourcethat is set at LOW volume. It is important to connect thebattery first, audio jack second.

4. If the transmitter LED's are pointed at the photodiode, youshould hear the transmission.

5. Turn up the volume of your audio source slowly until the soundis distorted slightly… then reduce the volume to the loudestundistorted setting. Leave the volume at this setting.

6. Try moving the receiver away, try pointing the photodiode indifferent directions to get a feel for the sensitivity

Using a microphoneTo use a microphone with your transmitter, connect a microphone tothe audio jack input. It is best to use an electret microphone. Theserequire that you make an additional connection from the microphoneto the positive power supply via a resistor of about 1k ohm typically.Refer to the manufacturers instructions. You can solder this resistordirectly to the positive side of R2 or the positive side of R5 and theother side of the resistor to the appropriate pin of the microphone.Some electret mikes have a resistor built in, and have three wires.Simply connect the microphone as per the manufacturers instructions.For a list of suppliers that carry electronic parts see the appendix.


Things to Try

Extending the rangeThe range of the transmitter / receiver pair is limited by the amount ofcurrent that can be safely applied to the LED's, the distance betweenthe LED's and the photodiode detector, whether there is anyintervening medium between the LED's and the photodiode.

Increasing the power. One simple change to the circuit would involvepowering the transmitter circuit from a higher voltage battery. DoNOT exceed 18 volts. Resistor R7 would have to be changed andincreased in wattage and a heat sink should be placed on thetransistor. The maximum current that the LED's can handle is 130mA. One should take care to leave enough margin and operate awayfrom this maximum - operation at the max rating will reduce the life ofthe component. Assume that the voltage you apply is V, and thecurrent through the LED's is ILED. The resistor R7 will have a value of Rand can be calculated from this formula:

R = [V/2 - 3.3] / ILED

and the power rating of the resistor must be greater than or equal to

Resistor power rating = ILED2 x R (in watts)

Suppose that we wanted to operate the LED's with a current of 100mA (=0.1 amps), and we chose a supply voltage of 18 volts. Then theresistor R7 should be equal to [18/2 - 3.3] / 0.1 = 57 ohms. Thepower rating of this resistor would be (0.1)2 x 57 = 0.57 watts.

Optical collimating. Although the above method is simple, the rangewould not increase greatly. A more dramatic increase in the range canbe achieved by using optical lenses in front of the transmitter andreceiver. Magnifying glasses could be used. The idea would be toplace the lenses at the focal distances from the LED's and thephotodiode. Using this method the range of the devices can beextended to hundreds of feet at night.


The focal length of the lens f will be slightly longer for IR light than forvisible light. To determine f for your lens, focus the light from adistant light source (e.g. a light bulb from across the room) onto asheet of white paper. Try to get as clear an image as possible.Measure the distance from the lens to the paper. This will be the focallength at visible light frequencies. The focal length for IR light will beslightly longer than this. A larger diameter lens at the detector will bebetter. The lens at the transmitter only need be large enough tointercept the cone of light from the LED's, which emit in a cone angleof about 20 degrees.

Adjust the focus of the lens for maximum sound transmission (youmay need walkie-talkie's and a friend to help you set this up). Thefarther apart that the transmitter and receiver are, the more difficult itwill be to align them. Practice using a light bulb instead of the IRtransmitter. Then substitute the transmitter.

You might also try to place the detector photodiode at the 'bulblocation' of a flashlight reflector. That is, remove the reflector from anold flashlight (be careful not to cut yourself). Place the diode detectorwhere the bulb would have been, but facing backwards towards thereflector instead of away. The reflector is a paraboloid, and the bulblocation is the focus. Parallel rays of light entering the reflector aredirected towards the focus.

Reducing interferenceYou may have noticed that when the receiver is operated in roomlights, there is a humming sound in the speaker. This is due to the 60


Hz switching of the lights as described earlier in the text.Unfortunately there is no easy answer here. An FM circuit could avoidthis problem, but here are some things to try:

Create a tube to shield the photodiode from overhead lights and aim itat the transmitter.

Dim the lights or shut them off.

Increasing the range of the transmitter can increase theunderstandability of the signal, although it won't reduce the noiselevel.

Reduce the gain of the receiver by changing the 820 ohm resistor to alarger value. If this is coupled with increasing the range and power ofthe transmitter and a shield for the photodiode, a good compromisemay be achieved.

Sound QualityThe input capacitors on the transmitter and receiver are set at 0.1 uF.Try changing this value. Does increasing or decreasing the value ofthis capacitor affect the sound quality? What about changing thespeaker?

Transmission and Reflection MediaWhat materials can you find that block the transmission path? Thatdon't block the path? Can you find materials that block light, but thatdon't block the transmission? Try overexposed colour film negatives -sometimes the end of a set of negatives will contain dark sections.How do these behave?

What materials reflect IR light well? Bounce your transmitter signal offdifferent surfaces before receiving it with your receiver. Keep thesame relative positions between the transmitter and receiver duringthe comparison. Are materials that are good reflectors in the visiblerange necessarily good reflectors in the IR spectrum?

Other sources of IRUsing just your receiver alone will allow you to discover other sourcesof IR (that have an AC or changing component). Point your TV remoteat the receiver and try pressing different buttons? What happens?What does a light bulb 'sound like'? How about fluorescent lamps?Does sunlight have any components that vary in the audio range?Lightning flashes? Campfires? Computer monitors? TV screens?


Appendix A - The Resistor Color CodeA resistor's value can be determined from its colored bands. Use thistable to determine resistance values and tolerances.

Notice that the 4 colored bands are not centered on the resistor body,but start at one side and end in the mid region. Hold the resistor sothat the end at which the colors begin is on your left. The colors areread left to right.

The color of the first three bands determine its value while the fourthband determines the tolerance.

The first band gives the first digit, the second band gives the seconddigit while the third band gives the number of zeros to add.

COLOR 1st digit 2nd digit MultiplierBlack 0 0 1Brown 1 1 10Red 2 2 100Orange 3 3 1,000Yellow 4 4 10,000Green 5 5 100,000Blue 6 6 1,000,000Violet 7 7 10,000,000Grey 8 8 100,000,000White 9 9 1,000,000,000Gold - - 0.1Silver - - 0.01

The fourth band color may be Gold, Silver or no color. Gold indicates atolerance of 5%, silver indicates 10% while no color means 20%.

Example: A resistor's color bands, from left to right are: yellow,violet, orange, gold.

Yellow = 4


Violet = 7Orange = x1000So the resistor value is 47000 ohms

The 4th gold band indicates that the tolerance on this value is 5%.


Appendix B - List of SuppliersThere are several suppliers of electronic components in the Kitchener-Waterloo-Guelph area. Others are located in Toronto or vicinity. Inaddition, Radio-Shack still carries a few components of interest andmay have what you need. Active Components in Mississaugua alsosells to hobbyists.

Waterloo: Sayal Electronics, 440 Phillip Street, Unit 1Guelph: Neutron Electronics, 450 Woodlawn WKitchener: Orion Electronics, 40 Lancaster W

an esq summer camp project - july 2001light. there are ir lasers and ir light emitting diodes (ir...

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