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Intruder alarm / Burglar alarm based Home Security System


Himanshu Choudhary

This electronic device is designed to alert the user to an intrusion. The project consists of a sensor and a control unit which are connected to each other. The sensor detects the interruption whenever an object or person comes between its transmitter and receiver. This interruption results in a signal generation which is supplied to a speaker.

This way whenever an intrusion takes place, the speaker goes on. Such devices are installed at various locations in houses or offices, especially near doors, windows.

In this project, the transmitter part of the circuit is an Infrared (IR) Led which transmits continuous IR rays to be received by IR receiver. The reception of rays at IR receiver results in high voltage at the output. The output of this IR sensor remains low when no signal is received. 



The output of IR sensor is connected to the Reset pin (Pin 4) of NE555 in accordance to the push-pull concept. The Reset pin of NE 555 is active low, i.e., the output of NE555 remains low (0V) when the input voltage is low, regardless of the threshold voltage. The output frequency can be adjusted by different value combinations of resistors R1, R2 and capacitor




The transmitter and receiver are placed such that an interruption is observed when the receiver receives reflected IR rays. In this case, the output of sensor and therefore the Reset pin remains high. Under such condition NE555 starts generating pulse of certain fixed frequency. The output of NE555 is filtered by a capacitor C2 (1uF) and fed to a speaker. Many sensor modules can be installed at different locations in a house or office and their outputs can be used to feed the Reset pin of a common NE555. Whenever any of the sensors detect the IR pulse, the RESET pin will go high and eventually the speaker will produce sound.


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...

LEDs | Light Emitting Diode
Light emitting diodes (LEDs) are semiconductor light sources. The light emitted...
IR LED | Infrared LED
Infrared LED
An IR LED, also known as IR transmitter, is a special purpose LED that transmits infrared rays in the range of 760 nm wavelength. Suc...
Presets | Variable Resistors
A preset is a three legged electronic component which can be made to offer varying resistance in a circuit. The resistance is varied by adjusting the rotary control over it. The adjustment can be done by using a small screw driver or...
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...
555 Timer | IC 555 | NE555
555 Timer IC

555 is a very commonly used IC for generating accurate timing pulses. It is an 8pin timer IC and has mainly two modes of operation: monostable and astable. In monostable mode time delay of the pulses can be precisely controlled by an external resistor and a capacitor whereas in astable mode the frequency & duty cycle are controlled by two external resistors and a...

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