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I have got some PCB that has an IR receiver and processes that signal in a non-relevant way.

I would like to intercept or snoop in on that same signal with an ESP8266, without affecting the original PCB's functionality, but I'm somewhat stuck in finding the right parts. Also, using a second receiver is not an option, because I need both controllers to receive the exact same signals at all times.

What I've conceptualized is using an optocoupler with the IR receiver's data line as the input, and the output going into a microcontroller's pin. Unfortunately, I wasn't able to find an optocoupler that wouldn't invert the signal. I would prefer for the signal to not be inverted for less difficulty in setting up the code.

Another option I found, is using a different kind of digital isolator, e.g. Texas Instruments ISO7310, as it doesn't invert the signal and appears to support a high signaling rate. My only worry is that with this circuit, I need to provide both supply and input voltage on the unknown PCB side, meaning I would have to split the data line in parallel, rather than in series. I'm not exactly sure how to pull that off without disturbing the PCB's original functionality.

I'm yet to open up the device I'm looking to modify, so I couldn't take any measurements yet. However, I preferred to check with this forum, if my thought process is correct. What are my options, is using the linked IC a good idea, what to watch out for to not interfere with the original functionality?

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  • \$\begingroup\$ Welcome! Please elaborate on ”Unfortunately, I wasn't able to find an optocoupler that wouldn't invert the signal. I would prefer for the signal to not be inverted for less difficulty in setting up the code.” Inverting the input in code seems like the simplest solution imaginable. Please note that you are loading the original circuit by using an optocoupler. \$\endgroup\$
    – winny
    Feb 21 at 20:37
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    \$\begingroup\$ Optocouplers don't invert a signal when used properly. However, it is unclear how you intend to use an optocoupler to begin with. And you can't assume the IR receiver can even drive an extra optocoupler, so it seems you have an XY problem, you want to sniff the signal, determined that optocoupler is the solution, and then asking how to do it with optocoupler. You should be describing the two circuits. Why the two circuits cannot be just connected together for example? \$\endgroup\$
    – Justme
    Feb 21 at 21:11
  • \$\begingroup\$ No, I'm specifically asking "What are my options, is [this] a good idea?". I wouldn't be here if I were all set and certain about using an optocoupler. I want to keep the circuits separate, because I don't know the internals of one of them. The circuits are as follows: Circuit 1 connects V1, Data1, GND to an IR receiver. I want to "clone" the digital signal on Data1 to Circuit 2. I planned on using for example a digital isolator with V2, Data2, GND2 connected to Circuit 2 in a configuration where Data2 follows Data1's digital signal. \$\endgroup\$
    – Opisek
    Feb 21 at 22:08
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    \$\begingroup\$ What is the goal of using the optocoupler vs just reading the signal directly with the ESP GPIO pins? \$\endgroup\$ Feb 21 at 23:17

2 Answers 2

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For non-interferance design in an isolated supply (I drew a battery but you can use an isolated DC-to-DC module) to power the input side of the optocoupler and the amplifier that allows connection to the infrared receiver signal.

schematic

simulate this circuit – Schematic created using CircuitLab

The output is inverted? Well that depends on how you wire up the output.

If you can find a point inside the device where you can connect the 5 V (or 3.3 Vetc) input then you don't need the dc-dc converter.

I need both controllers to receive the exact same signals at all times.

That's not going to happen. It will be very hard to predict which marginal signal the other controller will accept and which it will ignore.

If you want both to receive the same signal make the new controller receive the signal and then if it understands the signal generate a cleaned-up copy of the signal to send to the old circuit.

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The IR signal used for remote controls usually uses a carrier (38 kHz is common.) The IR receiver demodulates this signal to the baseband data line. So you don't have access to the 'raw' IR signal directly.

Optocouplers typically idle in the 'high-Z' state, then go low when receiving signal. The output is pulled up by a resistor.

The optocoupler data output should be buffered (I suggest an n-FET) which could then be used to drive the optocoupler's LED.

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