Tag Archives: Alarm Siren

Two Tones (Ambulance) Alarm Circuit

Posted on December 8, 2010 by Rend

Using very popular multivibrator 555 IC, we can build an alarm circuit which is similar to old ambulance siren. There are two sections inside the circuit, first is a low frequency oscillator for two level frequency modulation, and the second … Continue reading →

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Ambulance (Hee-Haw) Siren

Posted on July 18, 2010 by Rust
Ambulance 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 … Continue reading →

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Fastest Quiz Bell/Alarm

Posted on June 25, 2010 by Rend
QUIZ TIMER

This is aquiz bell/alarm circuit. This circuit indicate “fastest finger first”. This circuit has one bulb for Quiz master and one for each contestant. The bulb will illuminate when a button is pressed. the cathode of the 9v1 zener sees … Continue reading →

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