marconi challenge: infrared data transmission as the

Marconi Challenge:Marconi Challenge:Infrared Data TransmissionInfrared Data Transmission

as theas the2121stst Century Crystal RadioCentury Crystal Radio

Dennis SilageDennis SilageECE Temple UniversityECE Temple University

2006 ASEE K2006 ASEE K--12 Workshop12 Workshop

Marconi ChallengeMarconi Challenge


•• A simple and A simple and inexpensive yet inexpensive yet challengingchallengingprojectproject



•• 2121stst century crystal century crystal radioradio



•• Guglielmo MarconiGuglielmo Marconi pioneered pioneered wireless telegraphy at awireless telegraphy at awavelength of aboutwavelength of about1500 meters and1500 meters andsucceeded in sendingsucceeded in sendingan RF signal withan RF signal withkilowatts of power across the kilowatts of power across the Atlantic Ocean in 1901Atlantic Ocean in 1901



•• The The Marconi ChallengeMarconi Challenge forforstudents is to send anstudents is to send anIR signal at aIR signal at awavelength of aboutwavelength of about950 nanometers with 950 nanometers with milliwatts of power tomilliwatts of power toa detector over the largest a detector over the largest distancedistance



•• Inexpensive infrared Inexpensive infrared semiconductorsemiconductoremitter and detectoremitter and detector



•• IR emitter diodeIR emitter diode

•• 5 Volts5 Volts

•• 0.15 Amperes0.15 Amperes

•• 15 milliwatts15 milliwatts

•• 950950nanometersnanometers



•• IR emitter is aIR emitter is asemiconductorsemiconductordiodediode

•• No currentNo currentflow flow



•• IR emitter diodeIR emitter diode

•• Current flowCurrent flow



•• Ben FranklinBen Franklin’’sscurrent flowcurrent flow



•• Georg Simon OhmGeorg Simon Ohm

•• OhmOhm’’s Laws Law

V = I RV = I R



•• IR emitter diode IR emitter diode transmittertransmittercircuitcircuit

R1 = (3.2 R1 = (3.2 –– 1.3) V / 0.075 A1.3) V / 0.075 AR1 = 1.9 V / 0.075 A R1 = 1.9 V / 0.075 A R1 R1 ˜̃ 25 25 OO



•• Resistors in seriesResistors in series

V = I RV = I RV = I (R1 + R2)V = I (R1 + R2)

•• Equivalent resistor: Equivalent resistor: R1 + R2 R1 + R2 sumsum



•• Resistors in parallelResistors in parallel

V = I R V = I R R = V / I R = V / I 1 / R = I / V1 / R = I / Vnow now I = I1 + I2I = I1 + I21 / R = (I1 + I2) / V = I1 / V + I2 / V1 / R = (I1 + I2) / V = I1 / V + I2 / V1 / R = 1 / R1 + 1 / R21 / R = 1 / R1 + 1 / R2



•• Resistors in parallelResistors in parallel

1 / R = 1 / R11 / R = 1 / R1+ 1 / R2+ 1 / R2

•• Equivalent resistor:Equivalent resistor:R = (R1 R = (R1 ×× R2) / (R1 + R2)R2) / (R1 + R2)

product over the sumproduct over the sum



•• IR emitter diodeIR emitter diodetransmitter circuittransmitter circuit

•• Calculate R1Calculate R1

•• 0.075 A0.075 Adiodediodecurrent current



•• IR emitter diodeIR emitter diodetransmitter circuittransmitter circuit

3.2 V = (0.075 A) R + 1.3 V3.2 V = (0.075 A) R + 1.3 VR = (3.2 R = (3.2 –– 1.3) V / 0.075 A1.3) V / 0.075 AR = 1.9 V / 0.075 A R = 1.9 V / 0.075 A ˜̃ 25 25 OO

•• R1 is four 100 R1 is four 100 OO resistors in resistors in parallelparallel



•• IR detector phototransistorIR detector phototransistor

•• 70 Volts70 Volts

•• 0.05 Amperes0.05 Amperes

•• 850850nanometernanometer



•• IR detector phototransistorIR detector phototransistor

•• Like a transistorLike a transistorit but only has ait but only has acollectorcollector andandemitteremitter

•• PhotonPhoton input input



•• IR detector phototransistor IR detector phototransistor receiver circuitreceiver circuit




•• Sounder resistanceSounder resistance

R = V / I = 3 /.015 = 200 R = V / I = 3 /.015 = 200 OO




•• Calculate collectorCalculate collectorcurrentcurrent

I = (3.2 I = (3.2 –– 0.2) V / 2000.2) V / 200I I ˜̃ 0.015 A = 15 mA0.015 A = 15 mA




•• 15 mA sounder15 mA soundercurrentcurrent

•• 50 mA50 mAphototransistorphototransistor

maximum currentmaximum current




•• Sounder producesSounder produces70 dB intensity or70 dB intensity orabout 0.00001about 0.00001W/mW/m22



•• IR transmitterIR transmitter--receiverreceiver

Is the IR photodetector circuit Is the IR photodetector circuit sensitive to other sources? sensitive to other sources? Yes, Yes, incandescent lamps and bright incandescent lamps and bright sunlight can causesunlight can causethe sounder tothe sounder to

operate.operate.




Can you apply opticalCan you apply opticalprinciples to increase theprinciples to increase thedistance? distance? Yes, lens andYes, lens andmirrors can be used quitemirrors can be used quiteeffectively in lessoneffectively in lessonmodules on optics andmodules on optics and

ray tracing.ray tracing.




Can we encode information on the Can we encode information on the sounder? sounder? Yes, we can introduce Yes, we can introduce semaphores such assemaphores such asflagsflags, , Morse CodeMorse Code andandmodern modern ASCIIASCII coding.coding.




Can more advanced experiments be Can more advanced experiments be supported?supported? Yes, IR data Yes, IR data transmissiontransmissioncan be used tocan be used tointroduce digitalintroduce digitalsignaling.signaling.



•• Marconi Challenge PartsMarconi Challenge Parts

www.radioshack.comwww.radioshack.com Total cost Total cost ˜̃ $12$12RS 275RS 275--142 Infrared142 Infrared

emitter detectoremitter detectorRS 273RS 273--053 Mini053 Mini

buzzerbuzzer



•• Marconi Challenge PartsMarconi Challenge Parts

www.radioshack.comwww.radioshack.com TotalTotal cost cost ˜̃ $12$12RS 278RS 278--149 PC Board (2)149 PC Board (2)RS 270RS 270--401 AA battery 401 AA battery

holder (4)holder (4)RS 271RS 271--1331 100 1331 100 OO resistorsresistors

AA batteriesAA batteries



•• Marconi ChallengeMarconi ChallengeOptional PartsOptional Parts

Lens, mirrors, brackets,Lens, mirrors, brackets,ruler, telegraph keyruler, telegraph keyand an inexpensiveand an inexpensivedigital voltmeter.digital voltmeter.



•• A Challenge for You!A Challenge for You!

The simplicity and excitement of the The simplicity and excitement of the Marconi Challenge could be the 21st Marconi Challenge could be the 21st century equivalent of century equivalent of the crystal radio. the crystal radio.




The crystal radio provided the The crystal radio provided the impetuous for many high school impetuous for many high school students to turnstudents to turn--on toon toengineeringengineeringandandscience. science.




No, itNo, it’’s not an s not an iPodiPod but at least the but at least the students canstudents canunderstandunderstandhow it works!how it works!



•• For More InformationFor More Information

astro.temple.eduastro.temple.edu/~silage/~silage

www.arrl.orgwww.arrl.org



Dennis Silage,Dennis Silage, PhD K3DSPhD K3DSProfessorProfessorTemple UniversityTemple [email protected]@temple.edu

marconi challenge: infrared data transmission as the

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