- UM3561 is an 8-pin low-power sound generator chip consisting of a programmed mask ROM and a tone generator.
- The tone generator produces different tones depending on the information written by the ROM. This low-power and the low-cost chip is suitable for simulating siren sounds in alarm circuits and toys. Additionally, we can attach an external speaker through a bypassing transistor.
- SEL2 Sound Effect Selection Pin No.2.
- 2 Vss Negative of Power Supply.
- 3 OUTPUT Mono-tone Output.
- 4 NC Internal Testing Pin: Leave Open for Normal Operations.
- 5 Vdd Positive of Power Supply.
- 6 SEL1 Sound Effect Selection Pin No.1.
- 7 OSC1 External Oscillator Terminal 1.
- 8 OSC2 External Oscillator Terminal 2.
- UM3561 IC generates a multitone output signal.
- Pin7 and piN8 are used to control the frequency of the internal oscillator by connecting an external resistor(usually 220KΩ) between these two pins.
- These oscillations are then transferred to the control circuit which selects a tone based on the inputs of pin6 and pin2 select pins.
- Then the control circuit will pass this signal to the address counter and from the address counter to ROM and then to an output pin.
- An NPN transistor is usually connected at the output to amplify the sound since the sound signal produced is very weak.
To create a police siren circuit you need to create connections as per shown in the below circuit.
- Adjust IC UM3561 on the middle of the breadboard.
- Leave pin 1 unconnected and connect pin 2 with the ground pin battery.
- Connect pin 3 with the base of transistor BC547 using a 1k resistor.
- Connect the negative end of the speaker with the collector of the transistor and the positive end with the positive end of the battery.
- Connect the emitter of the transistor with the ground battery.
- Leave pin 4 unconnected and connect pin 5 with the positive of the battery.
- Leave pin 6 unconnected. Connect pin 7 and pin 8 using a 220k ohm resistor.