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Topic: Use IR Control Jack on av receiver (Read 5458 times) previous topic - next topic

Use IR Control Jack on av receiver

In my AV set-up, I have a TV that is controllable via a serial cable. This way I can turn my TV on and off using eventghost.
My AV receiver (NAD T752) however, lacks a serial port. The models that had one, were hundreds of euros more expensive at the time, so I decided to do without.
Since my receiver still puts out a decent sound, I would like to keep it for some more years. However I would like to control it via eventghost.
My receiver does have IR control I/O jacks and these are supposed to accept and transmit an unmodulated IR signal according to http://wiredremotecontrol.blogspot.com.

My question: How can I link an USB IR Toy to these jacks, so that I can control my receiver?
(Using IR transmission isn't an option, there is no LoS)

Re: Use IR Control Jack on av receiver

Reply #1 –
THe USB IR Toy is a very minimal platform focused entirely on IR.  If you want to interface to something which is not IR, then you can adapt just about anything if you have the wiring and coding skills.  Your best bet is probably the Bus Pirate, which you could wire to a 3.5 mm jack and plug in to your NAD T752.

I have my doubts that your NAD control jack speaks the same language as Pioneer SR, but who knows?

You could try using the IRToy to record the waveforms from your NAD remote, and those decoded signals might be just what you need on the control jacks.  Once you have the messages figured out, you could use the Bus Pirate to send them, or possibly wire a circuit between the IRToy serial port and the NAD, but this would require that you write custom firmware.  There are a lot of "if"s here, though.  The Bus Pirate is the easiest choice because you do not have to write firmware in order to do all the experiments you will need to discover the correct protocol for your NAD.

Re: Use IR Control Jack on av receiver

Reply #3 –
you could use only the IRtoy, get rid of the carrier signal with an appropriate low pass filter. this would leave you with only demodulated signal.
althouh a LPF may deform the data waveform a bit too much. could work though. you could also just put the IR led on a long cable to get it to the other room, telephone wire or something

fyi "accept and transmit an unmodulated IR signal" - unmodulated is not the right term, this would imply you only have a 40khz carrier, with no actual signal.. just nitpicking

Re: Use IR Control Jack on av receiver

Reply #4 –
[quote author="yaywoop"]you could use only the IRtoy, get rid of the carrier signal with an appropriate low pass filter. this would leave you with only demodulated signal.[/quote]The IR decoder hardware on the IRToy has already removed the carrier signal.  The IRToy only deals with a carrier when it is sending IR.
Quote
althouh a LPF may deform the data waveform a bit too much. could work though. you could also just put the IR led on a long cable to get it to the other room, telephone wire or something
That would not work because you would need to reintroduce the IR carrier if you use an IR LED.  However, since the NAD works without the IR carrier, you could just plug that long cable directly into the NAD control jack.  You'd need to make sure that the voltages are not going to damage the internal NAD electronics, but that might work fine.

Re: Use IR Control Jack on av receiver

Reply #5 –
The situation as I understand it is that Uome wants to control his receiver from his PC using an IRtoy from another room (as he said "I would like to control it via eventghost") so he would be sending IR from the irtoy, which would have a carrier as its intended to drive the LED

Actually just had an idea, you could actually use the on board ir decoder instead of a LPF to demodulate the signal (just make sure the IR led's light is making it to the IR receiver soldered next to it) then you would have the raw signal on one of the pins that can be fed into the control socket on the receiver (over a long cable if needed)

Re: Use IR Control Jack on av receiver

Reply #6 –
Hi Uome - interesting blog post. The blog post mentions that the protocol is the same as the IR Remote, but without the carrier signal. If you could find the remote code (eg with a universal remote), you could record the timing with the IR Toy. You could then definitely feed the timing in with a small microcontroller, but the IR Toy won't do that without modification. I could add a timing out mode that plays timing on the UART pins without the modulation, the eventghost plugin might need to be updated, I'm note sure it supports the IR Toy receive mode.
Got a question? Please ask in the forum for the fastest answers.

Re: Use IR Control Jack on av receiver

Reply #7 –
Since the IR Toy is only 20$, I'll buy one to experiment with. I'll let you know the results (or when I get stuck).

Re: Use IR Control Jack on av receiver

Reply #8 –
Since the IRToy hardware already has the UART wired to a header, you should have the minimal effort to get something working.

You want to be careful about directly connecting the UART to the NAD.  It might work that way, or you might need some minimal conditioning electronics between.  It's hard to say without information on the NAD circuits.  You could try identifying the circuit inside the NAD for clues, but don't electrocute yourself!

As for the firmware effort, if you can get MPLAB set up and compiling the existing open-source firmware, then it should be fairly easy to retransmit the demodulated IR signal to the NAD.

A sneaky alternative to the above would be to tap off of the IR decoder part in the circuit, condition the signal by buffering it, and then use that directly to feed the NAD.  This approach only allows live interaction with the IR remote, but you can run a very long wire to the NAD.