Optical Transmitter & Receiver

Project Number: 120

OBJECTIVE: To show how information can be transmitted using light.

Description: Build the circuit shown. Connect the photoresistor (RP) to the circuit using the red & black jumper wires. Place the photoresistor upside-down over the red LED (D1), so the LED goes into the photoresistor. Turn on both switches (hold down the press switch button). Music plays on the speaker, even though the two parts of the circuit are not electrically connected. The left circuit, with the LED and the music IC (U1) creates a music signal and transmits it with light. The right circuit, with the photoresistor and speaker, receives the light signal and converts it back to music. Here, the photoresistor has to be on top of the LED to work, but better communication systems (such as fiber optic cables), can transmit information over enormous distances at very high speeds.