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I'm i need to capture IR signals in their raw form from IR remote to analyze them. Currently I'm doing it by connecting logic analyzer directly across led on the remote. I want to skip that step and make a universal receiver that does not demodulate a signal and use IR led as receiver instead of photo-diode or photo-transistor.

I know that it's possible to use single IR led as both receiver and transmitter but not at the same time(which is logical) because there are TV remotes that have programmable buttons and you just point the original remote to the IR led at the top(I'm sure that led is used as receiver because there is no other optical component).

Can someone explain it to me how to use IR led for receiving raw IR signal and provide me with basic schematic?

It needs to have fast rise and fall times(probably simple to do, leds have fast response time).

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    \$\begingroup\$ While you can use an LED as a photodiode, I expect your remote control actually uses an integrated module that has IR LEDs and a photodiode in one housing. \$\endgroup\$
    – JRE
    Commented Oct 5, 2019 at 11:26
  • \$\begingroup\$ @JRE even more so: typical IR receivers also incorporate a demodulator (typical IR remote OOK signals are modulated onto some high frequency oscillation) and modulator. \$\endgroup\$ Commented Oct 5, 2019 at 11:43
  • \$\begingroup\$ @JRE Thanks about that information, i didn't know that there is photo diode and led in same case. I will check it. \$\endgroup\$
    – Nicky
    Commented Oct 5, 2019 at 11:52
  • \$\begingroup\$ Use a standalone photodiode. If you can put it right in front of the remote it may generate enough signal in photovoltaic mode (< 0.5V) otherwise you'll need a suitably high bandwidth amplifier stage. \$\endgroup\$
    – user16324
    Commented Oct 5, 2019 at 13:14

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An infra-red LED can detect the raw infra-red signal from a remote. An oscilloscope can view the voltage across the LED (diode). A standard oscilloscope appears as a 1MEGohm resistance, in parallel with some capacitance (perhaps 25pf). The diode itself adds some capacitance as well.
If you use a 1X oscilloscope probe, its additional capacitance will cause pulse distortion, so that diode voltage is not representative of the infra-red signal. You must sacrifice sensitivity by loading the diode with additional resistance. A loading resistor made too large slows response time for short light pulses:

schematic

simulate this circuit – Schematic created using CircuitLabToo-long RC time constant for short IR pulses
You can improve sensitivity by using a larger-value loading resistor, with no oscilloscope cable (diode and resistor mounted right at the 'scope input jack).
In any case, the IR remote will have to butt-up very close to the LED sensor...this is far less sensitive than the infra-red receiver chip, some of which can sense a signal from many meters away.


An Infra-red LED can be used as a photodetector in an opamp circuit. It is still not tremendously sensitive, but is fast enough to detect pulses from nearly any remote source butted-up to the sensor LED:

schematic

simulate this circuit 40kHz IRremote pulses received with op-amp circuit

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