Are you fascinated by automatic doors that opens by itself everytime you come close to it. Or don't you know yet how that particular door knows or senses the proximity of a moving object? Or perhaps you know the electronic principle behind it and wants to build the circuit. Most probably, the door has a special infrared switch module that is activated when the moving object interrupts its infrared beam. Such a module is very interesting to construct. It can control many types of electrical or electronic devices not just doors. A working system consists basically of a transmitter module which radiates the infrared beam, and a receiver module which captures this beam. Everytime this beam is interrupted, the receiver circuit is activated.

Printed Circuit (Transmitter module)

Parts Placement Layout (Transmitter module)

The infrared (IR) switch featured here can be used as monitor in alarm installations, sensor in sports or optoelectronic switch in counter installations, etc. It activates when the IR beam is interrupted. It is made of two parts: the transmitter module and the receiver module. Circuit 33.0 shows the transmitter module. It is basically a squarewave generator producing a frequency of 10 kHz. The duty cycle is around 1:3. This is then converted by the infrared diodes into a pulsating infrared beam.

Receiver Module

In normal situtations, the IR beam is being received continuously by the receiver module (diagram 33.1). This module is basically a combination of preamp and a demodulator. When the IR beam is interrupted or broken, the relay in the receiver module activates and latches. At the same time, the receiver module generates a tone. After 5 seconds, the tone will stop but the relay will remain in its latched position even if the IR beam is restored. The relay will release only when the reset button S1 is pressed.

Printed Circuit (Receiver module)

Parts Placement Layout (Receiver module)

Figures 33.1.0 and 33.1.1 show the printed circuit board for the receiver module. The receiver module must be housed in a light proofed case. Only the infrared sensor D1 must be exposed in such a way that the infrared beam coming from the transmitter hits it.

Electronic Circuits volume 1.0 - Circuit Nr. 10

The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com. Click on the image to view the book.