Emergency Siren
Électronique / Electronic
NE5532

The sirens we built in Projects ("Hand-Operated Sweep Oscillator" and "Falling Bomb Sound," respectively) change pitch only in one direction, but this one makes a low sound that becomes higher, and goes back to its original low sound. The siren sounds only once when you press the key. Assemble the circuit after setting the switch to position OFF. Turn on the siren by sliding the switch to position ON.

When you press the key the siren starts over at the original low pitch. Do you hear the siren sound change pitch as you expected?

IC 1 is an oscillator that produces current that forms a triangular wave, so when you press the key, it produces a triangular wave output. Then the output is sent to IC 2 which acts as an astable multivibrator.

In projects Hand-Operated Sweep Oscillator" and "Falling Bomb Sound, and this projects the astable multivibrator produces the siren sound and the pitch changes according to the values of R3 and C3.

Find out how the pitch changes when you set C3 to 0.02μF and then to 0.1 μF.