Marconi Challenge: Infrared Data Transmission as the 21 st Century Crystal Radio Dennis Silage ECE Temple University 2006 ASEE K-12 Workshop

Marconi Challenge:Marconi Challenge:Infrared Data TransmissionInfrared Data Transmission

as theas the2121stst Century Crystal Radio Century Crystal Radio

Dennis SilageDennis SilageECE Temple UniversityECE Temple University

2006 ASEE K-12 Workshop2006 ASEE K-12 Workshop

Marconi ChallengeMarconi Challenge


• A simple and A simple and inexpensive yet inexpensive yet challenging challenging project project



• 2121stst century crystal century crystal

radio radio



• Guglielmo MarconiGuglielmo Marconi pioneered pioneered wireless telegraphy at a wireless telegraphy at a wavelength of about wavelength of about 1500 meters and 1500 meters and succeeded in sending succeeded in sending an RF signal with an RF signal with kilowatts of power across the kilowatts of power across the Atlantic Ocean in 1901 Atlantic Ocean in 1901



• The The Marconi ChallengeMarconi Challenge for for students is to send an students is to send an IR signal at a IR signal at a wavelength of about wavelength of about 950 nanometers with 950 nanometers with milliwatts of power to milliwatts of power to a detector over the largest a detector over the largest distance distance



• Inexpensive infrared Inexpensive infrared semiconductor semiconductor emitter and detector emitter and detector



• IR emitter diodeIR emitter diode

• 5 Volts5 Volts

• 0.15 Amperes0.15 Amperes

• 15 milliwatts15 milliwatts

• 950950 nanometers nanometers



• IR emitter is aIR emitter is a semiconductor semiconductor diode diode

• No currentNo current flow flow



• IR emitter diodeIR emitter diode

• Current flowCurrent flow



• Ben Franklin’sBen Franklin’s current flow current flow



• Georg Simon OhmGeorg Simon Ohm

• Ohm’s LawOhm’s Law

V = I RV = I R



• IR emitter diode IR emitter diode transmitter transmitter circuit circuit

R1 = (3.2 – 1.3) V / 0.075 AR1 = (3.2 – 1.3) V / 0.075 AR1 = 1.9 V / 0.075 A R1 = 1.9 V / 0.075 A R1 ≈ 25 ΩR1 ≈ 25 Ω



• 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 diode transmitter circuit transmitter circuit

• Calculate R1Calculate R1

• 0.075 A0.075 A diode diode current current



• IR emitter diodeIR emitter diode transmitter circuit transmitter circuit

3.2 V = (0.075 A) R + 1.3 V3.2 V = (0.075 A) R + 1.3 VR = (3.2 – 1.3) V / 0.075 AR = (3.2 – 1.3) V / 0.075 AR = 1.9 V / 0.075 A ≈ 25 ΩR = 1.9 V / 0.075 A ≈ 25 Ω

• R1 is four 100 R1 is four 100 ΩΩ resistors in resistors in parallel parallel



• IR detector phototransistorIR detector phototransistor

• 70 Volts70 Volts

• 0.05 Amperes0.05 Amperes

• 850850 nanometer nanometer



• IR detector phototransistorIR detector phototransistor

• Like a transistorLike a transistor it but only has a it but only has a collectorcollector and and emitteremitter

• PhotonPhoton input input



• IR detector phototransistor IR detector phototransistor receiver circuit receiver circuit




• Sounder resistanceSounder resistance

R = V / I = 3 /.015 = 200 ΩR = V / I = 3 /.015 = 200 Ω




• Calculate collectorCalculate collector current current

I = (3.2 – 0.2) V / 200I = (3.2 – 0.2) V / 200 I ≈ 0.015 A = 15 mA I ≈ 0.015 A = 15 mA




• 15 mA sounder15 mA sounder current current

• 50 mA50 mA phototransistor phototransistor maximum current maximum current




• Sounder producesSounder produces 70 dB intensity or 70 dB intensity or about 0.00001 about 0.00001 W/m W/m22



• IR transmitter-receiverIR transmitter-receiver

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 and andmodern 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.com www.radioshack.com Total cost Total cost ≈ ≈ $12$12RS 275-142 InfraredRS 275-142 Infrared

emitter detector emitter detectorRS 273-053 MiniRS 273-053 Mini

buzzer buzzer



• Marconi Challenge PartsMarconi Challenge Parts

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

holder (4) holder (4)RS 271-1331 100 Ω resistorsRS 271-1331 100 Ω resistors AA batteriesAA batteries



• Marconi ChallengeMarconi Challenge Optional Parts Optional 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 turn-on tostudents to turn-on toengineeringengineeringandandscience. science.




No, it’s not an No, it’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.edu/~silageastro.temple.edu/~silage

www.arrl.orgwww.arrl.org



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

Documents

Marconi Challenge: Infrared Data Transmission as the 21 st Century Crystal Radio Dennis Silage ECE Temple University 2006 ASEE K-12 Workshop