Hand-Operated Sweep Oscillator
Électronique / Electronic
NE5532

The electronic buzzer we built in project Operational Amplifier Buzzer can only make a continuous beep, but we can make a similar circuit that produces various siren sounds. Now we're going to make a siren that gives out a sound with a variable pitch.

When you move the switch, this siren wails and then makes a continuous high-pitched noise. Slide the switch to position OFF and assemble the circuit.

When you finish the wiring, turn the power on by sliding the switch to position ON. You hear the speaker give out a sudden, roaring siren sound. The sound is low at first and becomes higher, then changes to a steady tone in about 3 to 4 seconds.

When you press the key and release it, the capacitor discharges and starts the siren sound again. Refer to the schematic.

U1:A works as a buffer and U1:B as an astable multivibrator. The pitch changes when the 100K ohm resistor increases the voltage applied to the 10 uF capacitor.