IR Remote Control Modulation Detector

Posted on Feb 5, 2014

A circuit to extract and measure the modulated carrier of an Infra Red remote control. Note that the circuit does not physically separate control pulses from modulation, but amplifies the completereceived signal allowing the waveform to be displayed ideally on an oscilloscope or a frequency counter. Modulation frequencies between 1kHz and several

IR Remote Control Modulation Detector
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MHz may be measured. All remote controls employing Infra Red technology use digital control signals that are modulated with a higher frequency carrier wave. The carrier wave, which is invisible to the human eye is commonly modulated between 36 and 38KHz. However, some equipment i. e. Satellite decoders may use even higher modulating frequencies. The digital control signals are relatively slow compared to the carrier frequency, typically 100 to 200 bps (bits per second). The control pulses are sent in serial format and turn the carrier on and off. Fortunately, the control pulses of a typical remote control are long, compared to the faster modulated IR carrier wave. This very fact allows at least a few complete waveforms to be captured and measured, either on an oscilloscope or with a digital counter. As the carrier is continually being modulated, the waveform will need to be displayed with a digital counter has a variable trigger or with an oscilloscopes manual trigger control. Light interference from nearby fluorescent light sources may also interfere with the signal, so, for this reason, I recommend to place the remote control within a few inches of the photodiode. The detector is an IR photodiode, type TIL100. This is reverse biased via the 22k resistor and produces small changes in current when subjected to light in the IR spectrum. Ambient or steady light will produce a constant current through the photo diode, a remote...

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