Elenco Upgrade Kit SC100 to SC500 - Manual (Page 63)

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Project #274
Pressure Alarm
OBJECTIVE: To build a pressure alarm circuit.
Connect two jumper wires to the whistle chip (WC) as shown. Set the
control of the adjustable resistor (RV) to the far left and turn on the
switch. There is no sound from the speaker (SP) and the LED (D1) is off.
Tap the center of the whistle chip. The speaker sounds and the LED
lights. The whistle chip has a piezocrystal between the two metal plates.
The sound causes the plates to vibrate and produce a small voltage. The
voltage is amplified by the power amplifier IC (U4), which drive the
speaker and LED.
Place a small object in the center of the whistle chip. When you remove
the object the speaker and LED are activated. In alarm systems, a siren
would sound to indicate the object has been removed.
Project #275
Power Microphone
OBJECTIVE: To build a power microphone.
Use the circuit from project #274.
Replace the whistle chip with the microphone (X1), and hold it away from
the speaker (SP). Set the control of the adjustable resistor (RV) to the far
left. Turn on the slide switch (S1) and talk into the microphone. You now
hear your voice on the speaker. The sound waves from your voice vibrate
the microphone and produce a voltage. The voltage is amplified by the
power amplifier IC (U4) and your voice is heard on the speaker.