An Electronics Hobbyist in King Forrest's Court

By Robert Cong

Like many of you, I sometimes find myself wondering if I could solve a Forrest Mims Jameco Puzzler without any help. Just when I think I have the obvious answer, I turn out to be slightly off. Well, in Forrest's Jameco Puzzler: Voice Transmitter, I had no clue as to what the solution could be. Not that I would doubt the great Forrest M. Mims III, but I sort of doubted that the solution would really work. I set out to build a Photophone and hopefully prove one way or another if Forrest's solution would really work.

audio amplifier kit
Completed "Super Snooper Big Ear" Audio Amplifier Kit

This project creates a Photophone, which is a device that will transmit voice through light waves. It may sound a little intimidating at first, but it's a fairly simple project that just about any person with beginner-level experience can take on. The Photophone is an invention by Alexander Graham Bell in 1880, so this is not new technology at all. This project also proved to be a good way to better understand how the basics of voice communication and the foundation of fiber optic technology work.

Audio amplifier connecting the microphone input to
the solar module
Audio amplifier connecting the microphone input to the solar module

The first thing required is an audio amplifier. Jameco carries the "Super Snooper Big Ear" audio amplifier kit, which includes all the components needed to make the audio amplifier. Of course you'll need a soldering station as well. The through-hole components are very easy to solder and the instruction manual provides a schematic for correct placement of each component. When soldering the components, make sure not to include the microphone which will ultimately connect to the solar module. The solar module will act as the microphone.

inside look at the tube
Inside look at the tube where light waves will travel and hit the solar module

After soldering the rest of the components in the kit, you will need to add a speaker, as well as a 0.1µF capacitor. The speaker has a designated spot on the printed circuit board, but the capacitor will go in the positive terminal in place of the microphone, which will connect to the positive side of the solar module. The negative terminal of the microphone will have 22 AWG jumper wire connecting to the negative side of the solar module.

photophone transmitter
Photophone transmitter used to speak into and modulate light waves

Now that the PCB is completed, it's on to the receiver. Just like in the Jameco Puzzler, the tube was constructed out of a cardboard box. Using only a pair of scissors and some electrical tape (because it's black and doesn't reflect any sunlight), the tube was made as seen below. On one end of the tube, tape on the solar module securely, making sure that the terminals are still accessible. Remember that the inside of the tube should also be dark, so that direct sunlight cannot reach the solar module.

photophone system
The completed Photophone system

The Photophone transmitter was made out of a plastic water bottle, aluminum foil and a rubber band. Black electrical tape was placed around the edges to prevent any possible cuts or scrapes. Now, the Photophone is complete! Just pop in the 9V battery and you can begin testing.

When ready to begin testing, you should use the infrared remote method as mentioned in Infared Remote Control Tester Project. The speaker gives off a slight hum when certain buttons on the remote are pressed. This means that your amplifier is working correctly. Next, get a flashlight and reflect the beam of light off the aluminum foil and directly into the solar module. Keep angling the light until the speaker noise is the loudest possible in order to achieve to loudest volume from your voice. Once the angle is found, speak clearly and directly into the transmitter.

While I was successfully able to prove that it was possible to construct a Photophone using the parts available to the DJ in the Jameco Puzzler, I never achieved anything close to broadcast quality audio. The noise may be quite loud at times, I think you will quickly understand why the world is not communicating through Photophones. So for my money, Alexander Graham Bell's greatest achievement was the telephone. Nevertheless, my colleagues and I must have had something close to the same thrill Bell had when the Photophone actually worked!

Parts List

Description Manufacturer P/N
Audio Amplifier Kit AA-1D
Solar Module SP3-37
0.1µF Capacitor DC.1
Speaker 38MS30008
22 AWG Wire WJW-70B
9V Battery DURACELL PC1604
Electrical Tape 051128-60160
Aluminum Foil
Rubber Band
Plastic Water Bottle

Robert is a graduate from Cal Poly, San Luis Obispo in Electrical Engineering. He is originally from Lincoln Heights in Los Angeles, CA. His interests include sports, movies, music, and playing with cool, new gadgets.