Multi-Tone Siren Circuit

This Multi-Tone Siren Circuit enables the users to select Police, Ambulance, and Fire & Staccato siren with 8W amp O/P. The siren kits available in the market generate normally a single tone. With Multi-Tone Siren, one can generate different types of siren tones for different purposes like ambulance, police fire, etc. This unique feature of the circuit makes it versatile and useful in wide range of applications like burglar system, lift door open alarm, smoke detector and any other alerting application.
About the circuit :
Versatile UM 3561, 8 pin IC is used here to generate four different audible ones. Basically IC has built in oscillator, control circuit, address counter, ROM and Tone generator etc .The predefined programs generate different tones only with few external components. The IC operates at low voltage of 3 volts upwards. Its quiescent current is as low as 150 microamperes.
A single resistor between pin7 and pin 8 decides the frequency of oscillations. Pin 1 and 6 are tone selector pins. The center - off toggle switch S1 helps in selecting the tone desired in the output. Output is available on pin 3.The selection table gives the switch poison and tone selected. The power supply used is from eliminator or battery measuring about 3-9 volts. A zener D1 of 2.7 volts is used to regulate the supply forIC1. R2 is the biasing resistor for zener D1.

The AF section consists of IC2, which is low power audio amplifier IC specially designed to deliver 1 – 8 watts of power at 4 ohms load (Speaker).The output of this amplifier exhibits low distortion and low noise. The input to this amplifier is fed through pin 3 through variable resistance VR1 to adjust the input signal. This acts as volume control. The output of this amplifier (pin 7) is fed to the speaker.