IC UM3561 is a CMOS LSI IC commonly used in alarm and toy applications. It is able to generate Police Siren, Ambulance Siren, Fire Engine Siren and Machine Gun Sound just by changing simple connections. It is a low cost and low power IC which can work down to 2.4V. We need only a few additional components as this Integrate Circuits has built in oscillator and selector circuits.

 About IC UM3561

IC UM3561 – Block Diagram

Basic blocks of IC UM3561 are shown in the above block diagram. There is an OSCILLATOR CIRCUIT, which generates the necessary clock for the operation of the IC. The frequency of the oscillation is determined by the resistor connected to OSC1 (PIN : 7) and OSC2 (PIN : 8) of the IC. A 220KΩ resistor connected across these pins will provide satisfactory results.

Pin Diagram

UM3561 Pin Out

 Pin Description

There is a tone generator, which is able to generate different tones using the oscillator clock and according to the data given by the ROM. Each data stored in the ROM corresponds to each tone and it can be selected by using the address of the data location. Address of the tone is provided by the ADDRESS COUNTER section of the IC.

I already said that this IC can generate 4 different sirens. These 4 sirens require 4 different sequence of tone generation, that means 4 different sequence of address counting. The address counting sequence is determined by the CONTROL CIRCUIT and SELECTOR blocks of the IC. We can select 1 of 4 sirens using SEL1 (PIN : 7) and SEL2 (PIN : 1) of the IC.

NC – No Connection
X – Don’t Care

Police Siren Circuit Diagram

Police Siren using IC UM3561

 Fire Engine Siren Circuit Diagram

Fire Engine Siren usingIC UM3561

 Ambulance Siren Circuit Diagram

Ambulance Siren usingIC UM3561

 Machine Gun Sound Circuit Diagram

Machine Gun Sound IC UM3561

The siren signal generated by the IC is available at PIN 3. As these signals are very weak to drive a speaker, we need an amplifier. Here BC548 transistor is used as an amplifier.

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