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39
Project #101
Hissing Foghorn
OBJECTIVE: To build a transistor oscillator that can make a
foghorn sound.
Build the circuit on the left and move the adjustable resistor (RV)
setting. Sometimes it will make a foghorn sound, sometimes it will
make a hissing sound, and sometimes it will make no sound at all.
Project #103 Video Game Engine Sound
Modify the circuit in project #101 by replacing the 100kΩ resistor (R5) with the
photoresistor (RP). Move the adjustable resistor (RV) setting until you hear hissing
sounds, and then shield the photoresistor while doing so and you hear clicking sounds.
Remove the photoresistor (RP) from the circuit in project #102 and instead
touch your ngers between the contacts at points A4 and B2 on the base grid
while moving the adjustable resistor (RV). You hear a clicking that sounds
like the engine sound in auto-racing video games.
Project #102
Hissing & Clicking
Project #104
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 ber optic cables), can transmit
information over enormous distances at very high speeds.
Optical Transmitter &
Receiver
OBJECTIVE: To show how information can be transmitted
using light.
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