Infrared mains remote control Switch

Posted on Apr 9, 2012

The infra-red (IR) toggle switch project described here is aimed to provide control mechanism for electrical appliances that do not have remote operation features. The goal is to construct a black box where you can plug-in your 120V AC appliance and control ON and OFF operations with any modern IR remote control devices. Modern IR remote controls generate modulated pulse train of 38KHz frequency when any key on the remote is pressed. With the use of capacitive filtering we will convert the stream of pulses into one pulse regardless of the key entered. This way, we will be able to toggle a relay switch with any key pressed on the remote.

Infrared mains remote control Switch
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This project has been tested with varieties of IR remote control devices like that for TV, DVD, digital camera, etc., and it worked well. The TSOP 1738 IR receiver module detects the 38KHz input pulses received from the IR remote control device. Under stand-by condition, the output pin of the IR module is at logic High, and when it detects the train of pulses, they appear at its output. The output from IR receiver is fed to a PNP transistor (BC557) with a series base resistor of 4.7K. At the collector of the NPN transistor, the train of pulses will be inverted. There is a 10uF capacitor and 100K resistor connected from the collector to ground. The function of capacitor is to convert the train of pulses into a single pulse, and the resistor is to provide the discharge path for the capacitor. So lets see what happens when a key on the remote is pressed. During standby, the output of IR receiver module is High, so BC557 is cut off. The capacitor is fully discharged, and the collector of BC557 is at ground. When a key is pressed on the remote, the train of pulses arrived at the base of BC557 turns it ON and OFF very fast. When it is ON, the capacitor gets charged through the collector current of BC557, and when it is OFF, the capacitor starts to discharge through 100K resistor. But the train of pulses is so fast (38000 pulses per second) that the capacitor doesn't get chance to discharge. So, the bottom line is, every time...

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