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Door Alarm Circuit

2016-02-18 17:27  
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Optical Door Alarm Circuit

Here is an opticaldoor alarm circuitis easy to build and can be used in a variety of alarm applications. The compact alarm can also be used on some other equipment in addition to protecting the windows and doors (as a burglar alarm). It consists of a sender LED and a phototransistor receiver.

The door alarm has an easy way of working with just a block or release the block on the path between the infrared LED and phototransistor. When blocked, there is no output anything, and vice versa when the block is open, the output goes high and turn on the sound of the buzzer.

Door Alarm Circuit Diagram

The Optical door/window alarm consists of two 555 timer IC. The first IC serves as RC oscillator that drives the infrared LED at a frequency on a combination of value and 1K resistor and 4.7uF capacitor. 220 Ohm resistor serves as a current limiter that goes into LED. At the receiver, an IC 555 timer configured as a monostable oscillator to detect the incoming pulses at specific frequencies. When the frequency is not detected, the alarm sounds. Operation voltage of thedoor alarm circuitis 5V to 12V DC, and a single 9V battery can be used for this purpose.

Door Alarm Circuit Diagram

Door Alarm Circuit Diagram

The phototransistor type used in this circuit is the type MRD300 from Motorola is a 50mA / 250mW NPN phototransistor. Equivalent units that can be used to include TIL81, MTD6040, BPW14, L14G2, OP804, BPX43-3, also BPW40. In fact, each phototransistor can be used, and of course may vary according to a system response.

This simple security alarm circuit can be applied to places where possible. It may be useful for educational purposes for those who try to understand the workings of a simpledoor alarm circuit.

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