Elenco Projects 102-305 - Manual (Page 15)

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Project #120
OBJECTIVE: To show how information can be transmitted
using light.
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 inside 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 music IC (U1) creates a music signal
and transmits it as 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 for this to work, but better
communication systems (such as fiber optic cables), can transmit
information over enormous distances at very high speeds.
Optical Transmitter &
Receiver
Project #121
OBJECTIVE: To change the sounds of a multiple space war with
light.
The space war IC (U3) will play a sound continuously. Block the light
to the photoresistor (RP) with your hand. The sound will stop. Remove
your hand and a different sound is played. Wave your hand over the
photoresistor to hear all the different sounds.
Press the press switch down and now two space war sounds are
played. If you hold the press switch down the sound repeats. Press
the press switch again and a different sound is played. Keep pressing
the press switch to hear all the different combinations of sounds.
Space War Sounds
Controlled By Light