Circuit Project:Tiny Door Guard

This simple Door Chime
protects the door and gives a loud Alarm tone when there is an attempt
of theft. The circuit is too simple and battery operated. A Normally
Closed (NC) reed switch and magnet is used to trigger the circuit. Alarm
generator is the popular ROM IC UM 3561. This
8 pin IC has an inbuilt oscillator to generate 4 siren tones like,
Ambulance siren, Police siren, Fire brigade siren and Gun sound. The
different tones can be selected using its pin 6 connected to VCC,
Ground or not connected. Frequency of oscillation is determined by the
220K resistor connected to the pins 7 and 8 of the IC.UM 3561 is the low
power IC and its maximum voltage rating is 3 volts. So Zener diode ZD
is used to give 3 volts supply to IC. Medium power NPN transistor T1 amplifies the output pulses from IC1 to a loud siren.

Tiny Door Guard Circuit

Tiny Door Guard Circuit

Magnet can be a small sized one that is to be fixed in the door
using double sided adhesive tape. Fix the circuit board in the door
frame. Fix Reed switch in the door frame, very close to the door. So
that, when the door is closed, the magnet will pull the contacts of the
reed switch to break supply to the IC. When the door opens, contacts of
the reed switch make contact and IC gets power to give alarm.

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