Infrared Inputs on the back of AV Receivers - diyAudio
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Old 6th June 2003, 01:07 AM   #1
diyAudio Member
Join Date: Nov 2002
Location: New Zealand
Default Infrared Inputs on the back of AV Receivers

Has anyone built there own IR receiver to plug into the IR input sockets that are on the back of many AV receivers/pre-amps?

My NAD T752 has IR inputs and outputs in the form of mono 3.5mm miniplugs. I have been in contact with NAD, and they have said that the input is expecting a modulated signal and the outputs are demodulated. (One would assume the outputs are TTL level direct from the IR receiver module).

I'm gonna have a play this weekend by first trying just an IR module to drive the input direct (Most demodulate the signal, though they leave a small amount of it there that I hope may be enough) and then building a modulation circuit as well if that doesn't work.

I'd be interested in hearing from anyone who has done this before and got something working!

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Old 13th June 2003, 12:50 AM   #2
diyAudio Member
Join Date: Nov 2002
Location: New Zealand
Default I find it hard to believe I'm trailblazing, but here goes...

After searching high an low for some sort of precedent for this stuff, there appears to be not too much info about.

NAD has recommend Xantech devices - I believe that these output a modulated signal as required. I still don't know what levels are required, however.

I've decided to put together my own circuit and see what happens - I'll start with a demodulated signal (Just the IR receiver module inverted using a transistor+resistor) and see if the NAD likes that. If it still needs the modulation, I'll use a 555 timer to remodulate it. At this stage I can probably add an IR LED to check the circuit is passing IR signals correctly. Finally I'll increase the output voltage until the thing works.

Hopefully one of the above ideas will do the trick!

I'll let you all know what I got to work + post schematics etc later.

If anyone happens to have a Xantech Receiver module on hand I'd appreciate the output signal specs (voltage level, whether or not it's modulated - what frequency it is - is it TRUE=high or TRUE=low?)

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Old 13th June 2003, 01:01 AM   #3
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Join Date: May 2003
Location: Colorado
Hello -

I am only familiar with this function for Pioneer equipment. In this case, the output jack is taken directly from the IR receiver. Therefore it is de-modulated and inverted.

The input jack expects the exact same signal. If you connect an IR receiver to this jack, you're in business.

I would assume that your gear works the same. So you don't need to add the inverter stage you mentioned. I really think it is simpler than NAD made it sound.

Good luck,
Charles Hansen
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Old 13th June 2003, 01:29 AM   #4
diyAudio Member
Join Date: Nov 2002
Location: New Zealand
Default Thanks for the reply, Charles

I too presumed it was going to be a quick and easy thing - The output on the NAD is certainly demodulated - though it appears to have been inverted already.

I see no reason why they require a modulated signal - they should have the receiver and rear input in parallel is is obviously the case with the Pioneer products.

Perhaps one reason is so it is "industry standard". I believe that the Xantech products and others all use the same format, and this is a modulated signal. Xantech has a "Convertor" module for equipment that requires a stripped signal (no carrier) that does the demodulation first. I know that Marantz stuff needs this. According to NAD, their AV receivers are using the Xantech format - they have said this twice, so I guess I'm starting to believe it.

Anyway, I've devised a simple system that I'll try - first the demodulated signal, then if necessary I'll remodulate it and try that.

I'm sure I'll get it to work in the end.
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