So UM3561 activated and start producing sound with Speaker. This burglar alarm circuit is very simple, whenever PIR sensor detects any human body movement, its OUTPUT pin becomes HIGH, which is connected to UM3561’s Power supply PIN 5. So this property of Zener diode protects the UM3561 IC by preventing higher voltage supply to it. This voltage is called Breakdown Voltage or Zener Knee voltage. All the diodes allow flow of current in only one direction (forward), but Zener diode can allow current in reverse direction if the voltage goes beyond a certain limit.

Zener Diodes are just like the other diodes, with only one difference. Below is the table for 4 Playing modes, you can produce whatever sound you want. We can play four sound by using its 2 sound Effect selection Pins (SEL 1 and SEL 2), like here in our circuit we kept SEL 1 and SEL 2 open, to produce the Police Siren sound. Internal Testing Pin : Leave Open for Normal Operations Pin diagram and Pin description is given below, taken from its Datasheet: The output generated by the IC is not sufficient to drive a 8ohm small speaker, so to amplify the output of the IC, a transistor must be used at the output (PIN 3). UM3561 works in the range of 3-5 volts, voltage higher than 5V can damage the IC, so if we are using it with other circuit or using a high voltage source, a Zener diode must be connected, to protect the IC. It has inbuilt oscillators and circuitry to produce the sounds. It is a 8 pin IC, and only require a external resistor to work. UM3561 is a CMOS LSI IC which can generate four types of sound: Police Siren, Ambulance siren, Fire brigade siren and machine gun sound.

Project red buffer gate