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Infrared Toggle Switch

This infrared toggle switch can be controlled by any TV/VCR remote operating at 38kHz frequency. The circuit uses readily available, low-cost components and can be assembled on a small veroboard.

Infrared Toggle Switch Circuit

Fig. 1: Circuit of infrared toggle switch
Fig. 1: Circuit of infrared toggle switch

Fig. 1 shows the circuit of infrared toggle switch and Fig. 2 shows the pin configuration of TSOP1738.

An integrated infrared receiver module TSOP1738 (IRX1) is used here for signal detection. Components R1 and C1 decouple the power supply to this tiny device (receiver module). In idle state, i.e., in the absence of infrared signals, output pin 3 of IRX1 is at a high level. This disables the monostable wired around one part of the renowned dual-precision monostable CD4538 (IC1). Its Q output (pin 6) is connected to input pin 4 to prevent retriggering in active state. Components R2 and C3 determine the time period of monostable oscillations (around one second).

Fig. 2: Pin configuration ofTSOP1738

Circuit operation

When a valid infrared pulse train is received by module TSOP1738, its output goes low for a moment and, as a result, the monostable (IC1) is instantly triggered by the negative-going pulse at input pin 5. Now the flip-flop (IC2) is clocked by the output of IC1 and its Q output (pin 15) goes high. This energises the relay through transistor T1. Resistor R4 limits the current to the base of transistor T1 and freewheeling diode D1 protects the relay from back e.m.f.

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Upon receiving another pulse train from the remote handset, IC2 is again clocked by IC1 as explained above and its output toggles to de-energise the relay and disconnect the load from 230V AC mains.

For powering the unit, use regulated 5V DC. Capacitor C4 suppresses the noise and capacitor C5 acts as a buffer.

The article was first published in October 2006 and has recently been updated.



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