UM3561 is an excellent ROM IC that can generate Multi siren tones simulating Police siren, Ambulance siren, Fire brigade siren and Machine gun sound. This 8 pin low power IC can work down to 2.4 volts.
The UM 3561 is a low cost siren generator designed for use in toy applications. The IC has an inbuilt oscillator and tone selection pins. It is easy to make a siren generator with only a few external components. Only one external resistor and a speaker driver transistor are sufficient to make a simple siren generator.
Inside the 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 220 K resistor will give satisfactory results. The oscillations thus generated will be then transferred to a control circuit which function 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.
Pin 1 Tone Sel.2
Pin 2 Gnd
Pin 3 Output
Pin 4 NC- Used for testing purpose
Pin 5 +3V
Pin 6 Tone Sel .1
Pin 7 Osc 1
Pin 8 Osc 2
By changing the pin connections of Sel.1 (Pin6) and Sel. 2(Pin 1) it is easy to change the siren tones.
Sel 1Sel 2Tone
Pin 6 Pin 1
NC NC Police siren
+3V NC Fire Engine sound
Gnd NC Ambulance Siren
NC +3V Machine Gun sound
UM3651 Siren Generator Circuit Diagram
Absolute Maximum ratings
Supply voltage Min. 2.4VTyp 3V Max 3.5V
Operating current Min - -180 uA