Building a Wireless Infrared Alarm An infrared alarm is an alarm that works via infrared. Infrared is used as a sensor, from an infrared transmitter

Building a Wireless Infrared Alarm

An infrared alarm is an alarm that works via infrared. Infrared is used as a sensor, from an infrared transmitter to the receiver. When infrared rays are blocked by people who passing through it, the alarm will activate a buzzer. This Alarm
is suitable for use in a corridor or small gate to detect people through the door.
Because the media used is an infrared light so that this infrared alarm is also said as a wireless infrared alarm. Infrared alarm system is qui
te simple and easy to build by using some 555 timer IC with infrared sensors LD274 for the transmitter and SFH5110 for the receiver.
Infrared signal emitted by the transmitter is not carried out continuously. Instead, it is modulated on the carrier frequency of 36 KHz to pulse t
he IRED (Infrared Emitting Diode) on and off itself, is switched on and off at a rate of about 300 Hz. This is done because most of the infrared sensors, including infrared alarm suggested in this diagram does not respond well to the incident infrared light continuously.
This infrared alarm circuit is not designed per
fectly, still need to add filtering so as not to be affected by direct sunlight. This need for a receiver to receive the infrared sensor with good intensity. This infrared alarm system is also designed for distances of several meters, and for those of you of course is quite challenging if you can make an even more powerful.

Infrared Alarm Transmitter and Re
ceiver Circuit
The infrared transmitter consists of two oscillators built around TLC555 IC. IC1 is the 300-Hz generator, IC2, the 36-kHz source. The IRED type LD274 is pulsed at a relatively high peak current via driver transistor T1. If i
n your application the distance covered by the IR beam is relatively short, the value of resistor R5 may be increased to save on current consumption. Preset P1 is adjusted for a carrier frequency of 36 kHz exactly (failing test equipment, adjust it for the optimum range).

Wireless Infrared Alarm-Transmitter Receiver Circuit

The receiver is equally simple and also based on a CMOS 555. As long as the sensor picks up infrared light from the transmitter, the reset input of the 555 IC is held low and the buzzer is silent. Components D1 and C2 act as a low-frequency rectifier to cancel the effect of the 300 Hz modulation on the transmitter signal. When the infrared light beam is interrupted, the oscillator built around the 555 is enabled and starts to produce a warning tone.
The test values indicated in the infrared barrier alarm circuit diagram are average DC levels measured with a Digital Volt Meter, under light/no light conditions. In fact, most test points carry rectangular or sawtooth waveforms.