Elenco Upgrade Kit SC500 to SC750 - Manual (Page 39)

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Project #582
OBJECTIVE: To create a sound circuit.
Loud Sounds
Turn the slide switch (S1) on and you should hear a tone from the
speaker (SP).
Project #583
OBJECTIVE: To see and hear the output from the Space War
Swinging Meter
with Sound
Set the meter (M2) to the LOW (or 10mA) scale. In this project, you
will see and hear the output from the space war IC (U3). The power
amplifier IC (U4) amplifies the signal from U3 in order to drive the
whistle chip (WC) and meter. Turn on the slide switch (S1). The meter
deflects back and forth, as the LED (D1) flashes and the whistle chip
sounds. Replace the whistle chip with the speaker (SP) for a louder
sound. Note that the meter will deflect very little now. Almost all the
signal is across the speaker due to its low resistance.