The siren circuit is what importance in various alarm. For example : the emergency alert, burglar alarm circuits, Fire alarm circuits, Timer , sensor controls, etc. If we have not these circuit, We will not able to recognize the functionality of the circuit,we set out.
Operation of the circuit is Q1 and Q2 will work with R3, R4 and C2 is a frequency generator circuit with output connected to LED1 and speakers SP1. When I press the switch S1 to the C1 will begin to charge allows the voltage to pin B of Q1 increase other. The Q1 is working and Q2 is working with at the C1 charge full cycle will stop oscillator speaker is not.
The LED1 light and hold the release the pressure switch S1, resulting in C1 will start discharger through R3, Q1 to ground. The oscillator circuit sound Sirens in the lower out. If we press the switch S1 and then quickly leave many. The sound will be as continuous as C1 to charge and discharge alternately continuously.
This is simple circuit than upper.let’s build now!:) Simple Siren by 2N2907 Transistor