UM3561 IC Based Security Alarm

This switch, when hidden under the floor mat, triggers an alarm when the person walks over it. Mat switch can be used as a security measure in a restricted area. Just put the switches beneath the mat after regular intervals so that when anybody who puts his feet on switch will engage the alarm.

This circuit is built around the CMOS UM3561 IC which is mostly used in toys and alarms because of its low cost and power saving ability.

Advantage-

1 The circuit does not consume the battery current in standby mode therefore lead to longer battery life.

2 You can also stabilize 9V DC mains adaptor in place of the battery.

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Assemble the circuit and mount the switches under the mat. When anyone presses the switch, the signals are provided to the base of the transistor T1. The base voltage of transistor T1 increases in comparison to emitter voltage and T1 starts conducting. Conduction mode in T1 makes transistor T2 to start conducting which in turn switches on the MOSFET BS170. This will provide the supply to IC1 Pin 5 which makes the output pin 3 of IC1 high. This high is provided to Darlington pair transistor T4, T5 and the loudspeaker connected to it starts sounding. We have connected the Zener diode at pin 5 of IC1 because the operating voltage of UM3561 varies from 3V to 4.5V therefore excess voltage may damage the IC.

In the circuit, UM3561 IC generates a tone similar to police siren and resistor R6 is used to control its oscillation. You can also increase the number of switches to increase the capability of the circuit. (Also check the luggage security alarm circuit)