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UM3561 IC Based Security Alarm


Anjali Sethiya

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.



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.


Hidden Security Switch Alarm




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)


Circuit Diagram


Resistor Image

Resistor is a passive component used to control current in a circuit. Its resistance is given by the ratio of voltage applied across its terminals to the current passing through it. Thus a particular value of resistor, for fixed voltage, limits the current through it. They are omnipresent in electronic circuits.

Capacitor image

Capacitor is a passive component used to store charge. The charge (q) stored in a capacitor is the product of its capacitance (C) value and the voltage (V) applied to it. Capacitors offer infinite reactance to zero frequency so they are used for blocking DC components or bypassing the AC signals. The capacitor undergoes through a recursive cycle of charging and discharging in AC circuits where the voltage and curre...

BC548 | Transistor BC548
Transistor BC548

BC548 is general purpose silicon, NPN, bipolar junction transistor. It is used for amplification and switching purposes. The current gain may vary between 110 and 800. The maximum DC current gain is 800.

BC558 Transistor Image
Transistor BC558
BC558 is a general purpose PNP transistor. It is used in switching and amplifier applications. The DC current gain varies in range 110 to 800. It is also used as a complement for transistors BC546 to BC550.
Speaker Image
A loudspeaker (or "speaker") is a transducer that converts electrical energy into acoustical energy. When an electric signal is applied to the input pin of speaker, it generates sound waves. The other pin is connected to ground. A speaker is commonly used to produce sound in response to a sensor output. For example, in an...



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