UM 3561 Siren Generator Sometimes we need a Siren sound generator to add in a Burglar alarm circuit or in Robot based circuit. The simple solution is the Siren generator IC UM3561. By using only a few components around this IC, it is easy to make a Siren Generator. By selecting the Pin connection of Sel 1 (Pin 6) and Sel 2 (Pin 1) we can select different tones.UM 3561 is a programmed ROM IC with an inbuilt oscillator.
Only one external resistor and a speaker driver transistor are sufficient to make a simple siren generator. The IC requires 3 volts so it works off 2 Pen cells. If the power supply is a higher voltage , use a 3.1 volt Zener to regulate the power to the IC. Internal circuits of UM3561 Inside the IC, there is an Oscillator circuit and the frequency of oscillations is controlled by the external resistor connected to OSC 1(Pin 7) and OSC2 (Pin 8). A 240 K resistor is the recommended value but a 220K will give satisfactory results. Do not change this value, it will change the tone. The oscillations thus generated will be then transferred to a control circuit which functions based on the tone selection through the connections of SEL 1 (Pin 6) and SEL2 (Pin 1) . The control circuit passes the signal to an address counter and then to the ROM. The tone pulses thus generated will be available from the output pin 3. Since the sound is weak, an amplifier is necessary to get loud sound. A single NPN transistor will amplify the sound. If loud sound is needed, use a Darlington transistor. Speaker should be 8 ohms 0.2 watts. A small Mylar Speaker is an ideal choice. Tone Selection 4 Sounds like Police Siren, Fire Brigade sound, Ambulance Siren and Machine Gun sound can be selected by changing the pin connections of Sel.1 (Pin6) and Sel. 2(Pin 1).
