Photophone Re-invented

Abstract

The photophone, invented by Alexander Graham Bell in 1880, is a telecommunication device that allows transmission of sound waves through beams of light. Two key concepts involved are modulation and demodulation. Modulation is the process of varying one or more properties of a periodic waveform. Demodulation is extracting the original information-bearing signal from a carrier wave. There are two parts of a photophone, the receiver and the transmitter. The transmitter modulates the initial sound wave. The modulated signal is called the carrier signal. The carrier signal is a light wave carrying an audio clip. The light wave then is carried through a solar panel to an amplifier. The amplifier and capacitor demodulate the carrier signal, extracting the sound wave from the light wave. The sound wave is then sent to a speaker, playing the sound wave that was initially transmitted. The purpose of this project is to make a photophone that will serve as a basic prototype of an intergalactic photophone. Materials: Audio Amplifier Kit 3.3k Resistor 1k Resistor (3) 10k Resistors Trim Pot can be 5k, 10k, or $20\ \mathrm{k} 0. 1 \mu \mathrm{F}$ Capacitor 47uf Capacitor (2) 4.7uf Capacitor (2) 8 Pin IC Socket 9v Battery Snap 9v Battery Circuit Board Soldering Iron Solder Solar Module $0. 1 \mu \mathrm{F}$ Capacitor Speaker 22 AWG Wire 9V Battery Electrical Tape Aluminum Foil Rubber Band Plastic Water Bottle Cardboard Jumper Wire Alligator Clips Method: Create an Audio Amplifier (DIY Kit) Assemble the circuit board by placing each piece onto the corresponding location on a circuit board Solder each piece Attach a speaker to the circuit board Place the $0. 1 \mu$ Fcapacitor on the positive terminal of the microphone section of the amplifier Connect the other end of the $0. 1 \mu \mathrm{F}$ capacitor to the positive end of the solar panel Create a box out of cardboard. Then tape the solar panel to the end of the box. Add holes in the corners of the tube or box to allow a place for the alligator clips to connect to the solar panel Connect the negative end of the solar panel to the corresponding location of the amplifier Create a Transmitter Place a speaker behind a mirror. Adjust the transmitter until the sunlight is reflected down the box. Future Work/Applications: The photophone uses light waves to transmit sound over a certain area and time. This can be applied on a large scale. Challenges with using light waves to carry sound clips include that light on Mars can take over 3 minutes to travel between Earth and Mars. In spite of this, a future application can be an intergalactic photophone in which a person can transmit light waves across our solar system and be able to communicate with people back on Earth. This can be tested on the ISS, the moon and even a colony on Mars.