Security Alarm

Topics: Electronics, Physical security, Infrared Pages: 3 (559 words) Published: July 27, 2011
Infrared security alarm


Not so long ago an alarm was a fairly rare sight, however now almost every house has an alarm of some kind. One common kind of security system is an infrared home security system. These are so popular because they are easy to install without having to drill holes and lay cable infrared radiation is invisible to the human eye but can be detected by electronic devices designed for such a purpose.

The sensors are set at the door or some supervised area and an alarm is triggered when an intruder passes within its range of coverage to alert the security.

Principle of operation :

The complete block diagram of the security alarming system fig. below. The regulated low voltage power supply produces 5 V for IR transmitter and receiver, amplifier circuit, trigger circuit , driver circuit and buzzer.

The anode of the transmitter and receiver are connected to the 5 V power supply and cathodes are connected to the ground. When the bias voltage applied to the security alarm circuit, the transmitter emits the Infra-red ray. Then this connected to amplifier

to amplify the low sound coming from transmitter.

The amplifier tansmits the signal to the switching circuit which passes it to Trigger circuit . When trigger circuit gets the signal it drives to the buzzer or loud speaker through the help of driver circuit.

Hardware implementation [pic]

Circuit explanation:

The source is a high efficiency GaAs infrared emitting diode and the sensor is an NPN silicon phototransistor which has exceptionally stable characteristics and illumination sensitive. Bias voltage of (+3 and +5V ) is applied to the anode through resistor R 1 of the diode D5 and cathode is connected to ground. The signal is very weak and hence need to amplify.

The circuit uses an operational amplifier LM324. It helps to amplify the signal...
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