Marconi Challenge: Infrared Data Transmission as the 21 st Century Crystal Radio

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1 : Infrared Data Transmission as the 21 st Century Crystal Radio Dennis Silage ECE Temple University

2 A simple and inexpensive yet challenging project

3 21 st century crystal radio

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

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

6 Inexpensive infrared semiconductor emitter and detector

7 IR emitter diode 5 Volts 0.15 Amperes 15 milliwatts 950 nanometers

8 IR emitter is a semiconductor diode No current flow

9 IR emitter diode Current flow

10 Ben Franklin s current flow

11 Georg Simon Ohm Ohm s s Law V = I R

12 IR emitter diode transmitter circuit R1 = ( ) V / A R1 = 1.9 V / A R1 25 O

13 Resistors in series V = I R V = I (R1 + R2) Equivalent resistor: R1 + R2 sum

14 Resistors in parallel V = I R R = V / I 1 / R = I / V now I = I1 + I2 1 / R = (I1 + I2) / V = I1 / V + I2 / V 1 / R = 1 / R1 + 1 / R2

15 Resistors in parallel 1 / R = 1 / R1 + 1 / R2 Equivalent resistor: R = (R1 R2) / (R1 + R2) product over the sum

16 IR emitter diode transmitter circuit Calculate R A diode current

17 IR emitter diode transmitter circuit 3.2 V = (0.075 A) R V R = ( ) V / A R = 1.9 V / A 25 O R1 is four 100 O resistors in parallel

18 IR detector phototransistor 70 Volts 0.05 Amperes 850 nanometer

19 IR detector phototransistor Like a transistor it but only has a collector and emitter Photon input

20 IR detector phototransistor receiver circuit

21 IR detector phototransistor receiver circuit Sounder resistance R = V / I = 3 /.015 = 200 O

22 IR detector phototransistor receiver circuit Calculate collector current I = ( ) V / 200 I A = 15 ma

23 IR detector phototransistor receiver circuit 15 ma sounder current 50 ma phototransistor maximum current

24 IR detector phototransistor receiver circuit Sounder produces 70 db intensity or about W/m 2

25 IR transmitter-receiver receiver Is the IR photodetector circuit sensitive to other sources? Yes, incandescent lamps and bright sunlight can cause the sounder to operate.

26 IR transmitter-receiver receiver Can you apply optical principles to increase the distance? Yes, lens and mirrors can be used quite effectively in lesson modules on optics and ray tracing.

27 IR transmitter-receiver receiver Can we encode information on the sounder? Yes, we can introduce semaphores such as flags, Morse Code and modern ASCII coding.

28 IR transmitter-receiver receiver Can more advanced experiments be supported? Yes, IR data transmission can be used to introduce digital signaling.

29 Marconi Challenge Parts Total cost $12 RS Infrared emitter detector RS Mini buzzer

30 Marconi Challenge Parts Total cost $12 RS PC Board (2) RS AA battery holder (4) RS O resistors AA batteries

31 Marconi Challenge Optional Parts Lens, mirrors, brackets, ruler, telegraph key and an inexpensive digital voltmeter.

32 A Challenge for You! The simplicity and excitement of the Marconi Challenge could be the 21st century equivalent of the crystal radio.

33 A Challenge for You! The crystal radio provided the impetuous for many high school students to turn-on to engineering and science.

34 A Challenge for You! No, it s s not an ipod but at least the students can understand how it works!

35 For More Information astro.temple.edu/~silage

36 Dennis Silage, PhD K3DS Professor Temple University

The Marconi Challenge: Infrared Data Transmission as the 21 st Century Crystal Radio

The Marconi Challenge: Infrared Data Transmission as the 21 st Century Crystal Radio Dennis Silage, PhD Electrical and Computer Engineering Temple University silage@temple.edu Introduction The Marconi