Ambulance (Hee-Haw) Siren

The circuit below consists of two multivibrators. The first multivibrator provides the speed of the change from “hee” to “haw” and operates at a low frequency. By allowing full voltage to appear at the bottom of the 220R and then a slightly lower voltage when LED is illuminated will modified the voltage to the tone multivibrator.

Ambulance Siren