First Aid Siren
Électronique / Electronic
NE5532

The sirens we built in In the three previous projects ("Hand-Operated Sweep Oscillator," "Falling Bomb Sound," and "Emergency Siren," respectively) change the pitch of their sounds smoothly between low and high, but this siren is a little different. It gives off alternating high and low sounds.

Slide the switch to position OFF and assemble the circuit. After you finish the wiring and slide the switch to position ON, the power turns on and the speaker makes the sound of a two-pitch siren.

This siren is made up of two astable multivibrators. IC 2 provides the normal beep sound that we heard in Project ("Operational Amplifier Buzzer"), and IC 1 produces the signal that changes the pitch of its sound at regular intervals.

Let's perform a small experiment now. Detach the 22K ohm resistor, and you find that the siren gives out an intermittent beep instead of the two-pitch sound. Can you figure out why?

Yes, IC 1 interrupts the siren sound produced by IC 2.