The DIY Electronic Siren circuit described here can create three different US-style siren sounds: DIY police, DIY ambulance and fire engine. The desired sound can be selected using switch S1. The circuit can be used in toys (such as model vehicles), as part of an alarm system, and in many other applications. For use in a toy, a BC337 is an adequate device for driver T5, since it is capable of directly driving a 200mW (8Ω) loudspeaker. In this case the current consumption from a 9 V power supply is around 140 mA. If a louder sound is required, a BD136 is recommended: this can drive a 5W (8Ω) loudspeaker.This will be the sound produced with the switch S1 on this positions:
- a: Fire Brigade Siren
- b: Police Siren
- c: Ambulance Siren
The current consumption of the electronic siren from a 12 V supply will then be about 180mA. If still more volume is desired, then T5 (a BD136) can be used as a first driver stage, and a 15W (8Ω) loudspeaker can be connected via output transistor T6. Here an AD162 or an MJ2955 can be used, which, for continuous operation, must be provided with cooling. The peak current consumption of the circuit will now be about 500mA with a 12V power supply. Capacitor C1 is not required for battery operation.
Parts List
R1 = R9 = 2.2KΩ
R2 = 470Ω
R3 = 47KΩ
R4 = R8 = 22KΩ
R5 = R6 = R7 = 18KΩ
R10 = 3.3KΩ
C1 = 100µF/16V
C2 = 2.2µF/16V
C3 = 10µF/16V
C4 = 47µF/16V
C5 = 22nF
C6 = 33nF
C7 = 470µF/16V
T1 = T2 = T3 = T4 = BC547
T5 = see text
T6 = MJ2955, AD162
ref:http://electroschematics.com
