Rongge

How make a Simple Siren with Four Transistors. This circuit requires only small 6V power from the speaker to generate sound two tones. Simple Siren with Four Transistors Circuit Diagram The circuit is more than simple. The first two transistors (left) are responsible for forming a flip-flop. This means that the 10K resistor will have a pulsed signal. The 4.7μF capacitor is charged and discharged in this signal are almost pulsating. Applied this to the oscillator (formed by the other two transistors) we obtain the desired sound output. The speaker can be any 8 ohm 1 watt the type used in portable radios.

 Simple Siren Circuit Diagram This circuit will generate siren sound when S1 pressed and increate sound frequency becuase capacitor C1 charged when switch S1 released the frequency will decreated(C1 discharged). Try to change resistor R3 if you need to change time interval from low to high frequency and vise versa.

This circuit will generate siren sound when S1 pressed and increate sound frequency becuase capacitor C1 charged when switch S1 released the frequency will decreated(C1 discharged). Try to change resistor R3 if you need to change time interval from low to high frequency and vise versa.