Using this optical remote switch, you can switch on/off any electrical or electronic load. Like any remote control system, it has a mini transmitter unit (Fig. 1) and a receiver unit (Fig. 2) to activate the relay.
Optical remote switch: transmitter
The optical transmitter used is an astable multivibrator based on IC 555. Its frequency is 1 kHz. At the output of the transmitter, two high-intensity red LEDs driven by a pnp transistor are used. When the optical transmitter is switched on, the red LEDs glow. The emitted red light contains 1kHz code signal.
The optical transmitter works off a 9V PP3 battery. To achieve better performance and longer range, use a reflector in torch.
Optical remote switch: receiver
The receiver unit comprises a signal amplifier, switching circuit, flip-flop and relay. The signal (tone) amplifier boosts 1kHz audio frequency signals. The switching circuit applies pulse to the flip-flop circuit built around STMicroelectronics-make CMOS IC 4027.
For each input pulse, the output of CD4027 goes high and low alternately. High-to-low variations of the flip-flop are amplified by an npn transistor to energise the relay, which, in turn, controls the external load.
Use regulated 12V to power the receiver unit.
After connecting 12V DC supply to the receiver unit, orient LEDs used in the transmitter towards the sensor of the receiver (L14F). Press switch S1 of the transmitter momentarily. This will activate the relay. Pressing switch S1 again will deactivate the relay.
This optical remote control works satisfactorily in medium-lit and dark rooms.
The article was first published in October 2006 and has recently been updated.