Electronic Door Minder using 555 Timer

This door minder electronic project is based on a 555 timer circuit and uses an IR beam to monitor door and passage-ways or any other area. When the IR beam is broken a relay is tripped which can be used to sound a bell or alarm. This door minder electronic project is suitable for detecting customers entering a shop, cars coming up a driveway, etc. Because the IR beam is very strong distances over 25 yards can be monitored with electronic circuit .

The transmitter circuit consists of two square-wave oscillators, one running at approx. 250Hz and the other running at 38kHz.
The oscillators are made by using two 555 timer ICs set up as astable configuration multivibrators.

Another 555 timer ( IC2) is used for the 38KHz oscillator. Resistors R4 and R5 and capacitor C3 set the frequency.

The receiver module consists of an IR receiver module that detects the incoming beam from the transmitter. The IR signal is used to keep a capacitor charged which in turn holds a relay operated. When the beam is broken the capacitor discharges and the relay releases. This circuit must be powered from a 12volt DC supply.