IR Experts: Advice Needed on IR Receiver vs IR Input Signals

Posted on
Thu May 31, 2018 9:57 am
Swancoat offline
Posts: 480
Joined: Nov 20, 2009
Location: Houston

IR Experts: Advice Needed on IR Receiver vs IR Input Signals

I need some clarification on any differences between 'IR Input' and 'IR Receiver' input ports and what signals they take.

A couple of years ago, I switched to centralized video distribution in my home, with video carried on HDBaseT.

In most rooms, there's basically just a TV which connects to the HDBaseT receiver. The HDBaseT receiver has an IR receiver plugged into it and backhauls the IR back to the head end, where the distribution matrix uses emitters to control the AV devices. Works great.

However, in my living room, there are a few IR devices besides the TV, with equipment in the cabinet, so I have a Xantech distribution hub in the cabinet, and an IR receiver visible to the room. So the 'flow' of IR signal here is, from the IR Receiver to the Xantech Hub, and then from there to the TV and lift, as well as one output from the Hub going to the IR Input on the HDBaseT receiver (to backhaul signals back to the head end).

I want to have a wire running from the Xantech Emitter output plugged right into the IR IN port on the HDBaseT receiver, but cannot seem to get it to work at all. (Disclaimer. It actually does work right now, as I have a simple Xantech emitter taped to the front of an IR Reciever which goes into the HDBaseT receiver. However, I WANT to do it just with one wire with 3.5mm connectors on either end. Partially to appease my insanity, but mainly at this point, to learn more about exactly what is going on here).

Xantech: Emitters are 3.5mm mono connections. Tip: signal, Sleeve: ground.
HDBT Receiver: Input is 3.5mm stereo. Tip: Signal, Ring: 12VDC, Sleeve: Ground. (So one difference right away is the presence of the 12VDC, but since that port uses an IR receiver and those require power).

Plugging a 3.5mm stereo cable into each end results in nothing. Simply doesn't work. The stereo cable should still work on the Xantech end, but nonetheless, I made a new cable that was 3.5mm stereo on one end and mono on the other. Tip to Tip, Sleeve to Sleeve, and Ring on the stereo connector simply left unconnected. Still doesn't work.

(I have not plugged a mono cable in, since that would likely short the power supply in the HDBT receiver)

My initial thought here is that it's simply a different signal of some type. i.e. that what comes out of an emitter isn't exactly the same thing that a receiver sends out (and the distribution blocks do some conversion or something), but I'm not so sure of this...

Other data points:
1. In my media room, I have a distribution block plugged into both an AV Receiver and a Blu-Ray player via a 3.5mm audio cable going directly from a Xantech distribution block emitter output to 3.5mm ports labeled 'IR In' on those device, and that works fine. This tells me that either the signal from and emitter or a reciever IS the same, or else that those ports are specific 'IR In' which expects a distinctly different signal than an IR Receiver would provide. I have not tested them with connecting an IR Receiver to them. I also do not know what the TRS pinouts are on those ports.

2. I've also done some experimenting with the emitters from a logitech Harmony IR hub interfacing with a Xantech distribution block. The distribution block was using a Xantech IR receiver, connected to signal, gnd and 12VDC via the terminal block (not the 3.5mm connection). I disconnected the IR Receiver and connected the logitech Harmony IR hub via one of the blaster outputs. Tip: signal on the terminal block, and Sleeve to gnd. This worked as well, which seems to be conclusive evidence to me that the signal from an IR emitter/blaster IS the same as the signal coming from an IR receiver.

3. Some documentation in some Xantech manuals shows outputs from one connecting block connecting directly to the IR receiver inputs of another block (also suggest there's no signal difference).

4. There is the existence of the Global Cache GC-CGX, which is a cable that specifically 'converts' IR outputs from Global Cache iTach devices to suitable signal for a Xantech distribution block. (which now throws a wrench into everything, suggesting there definitely ARE differences between emitter signals and receiver signals. Or maybe it just means that Global Cache uses a weird pinout... (although that cable has a little 'box' on it that makes me think there's more 'converting' going on than just a different pinout) and in this case Global Cache emitters would necessarily be incompatible with Xantech emitters? Need to test this.).

When all is said and done, the balance of evidence makes me think that the signal from an IR receiver, and the signal to an IR emitter is basically the same 'signal'. Pinouts seem like they can vary a bit, but that can be dealt with. Unfortunately, that brings me back to my original issue around the HDBaseT Receiver. Why the heck doesn't this thing work? Does it have some proprietary receiver signal type? Is the documented pinout wrong?

Apologies for the long (much longer than I expected) post, but if you're still reading and have any knowledge to add, it would be greatly appreciated!

Posted on
Fri Jun 01, 2018 10:11 am
Swancoat offline
Posts: 480
Joined: Nov 20, 2009
Location: Houston

Re: IR Experts: Advice Needed on IR Receiver vs IR Input Sig

Just some followup from my own continued testing/experiences (for anyone who stumbles across this thread)...

It so happens I do have a Global Cache GC-CXG Cable at home (not to be confused with the GC-CGX). This cable is for connecting the emitter outputs of an IR distribution system (which is what I'm doing...) to the Global Cache GC-IRE input. Using this to connect my IR distribution to the HDBT receiver also doesn't work, but that appeared to be because Global Cache seems to use a more unusual ground-power arrangement for the ring and sleeve pins (as opposed to power-ground in other applications). So I cut a little 3.5mm extension cable and made it into a kind of crossover cable connecting tip-tip ring-sleeve and sleeve-ring. Using this crossover cable to connect the IR distribution to the HDBT receiver actually worked!

So, whatever 'conversion' that the global cache cable is doing in its little box seems to be what was required, and the signal is otherwise the same. I looked around a bit and all they really say is that the connection is 'optically isolated' (although I never opened up the box on the cable).

I had no idea what 'optically isolated' even means, so I looked into that too. Turns out it's to reduce noise and basically converts an electrical signal to light, and then back to electricity again so hums or surges can't travel across. Which is hilarious, because that's exactly what my cave-man solution of taping an emitter onto the receiver does. i.e. - IR Emitter + IR Receiver + some electrical tape = "Optically Isolated Cable". :D :D :D :D

So basically, I think my answer here is the the SIGNAL from an IR receiver, or an IR emitter is the same... but my HDBT receiver's IR input must be overly sensitive to noise or signal level or something.

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