IR help

[jesjohnson]

Hello,
I a trying to manipulate an IR signal by mimicking it with a microcontroller to control another. The other MCU is an OEM and I do not want to change it's programming. What I have tried to do is get all IR signals from the OEM remote, save them, and send them back to the device from the saved array. I want to use one of the I/O on the MCU to mimic the IR signal without using a transmitter/receiver., is this possible? So far all my attempts have failed and I wanted to know if there was anything I could do.

 

[hexreader]

Sounds like a job for a good DSO and/or a logic analyser connected to the transmitter IR LED.

Do you have either?

You can do it by programming your microcontroller to measure the timing at the LED (or perhaps the transmitter Tx pin) but that is much harder work.

What tools do you have available and how much effort to you want to put into this project?

Regards,

Robin

 

[Hippogriff]

I believe this would become easy with a Logic Analyser. I did something that sounds similar with a number of PICs (12F683s) and a TSOP... essentially I had a 'master' PIC which the TSOP was connected to, it would 'read' the commands (not 'recognise' them) and punt the same thing over to the other PIC(s). Basically, pin flipping based on the start of a falling edge interrupt on A2. My Saleae Logic helped me achieve that in no time (using a high-level language, JAL).

 

[Nigel Goodwin]

You first need to analyse the signal - while a DSO would be nice, there's a MUCH cheaper way.

Use an IR preamp IC, and feed that to your PC soundcard, you can then use Audacity to record your samples.

By recording the various buttons, you can work out how best to store and replicate them.

You might check my PIC IR tutorial, which I've used to duplicate various different remote types.

 

[jesjohnson]

Thank you guys for the quick reply!
Well what I have is really just my microcontroller with some receivers and transmitters. My reasoning was that I thought the IR receiver acted like a transistor with the gate being operated by the IR signal, therefore if I duplicate that signal I can skip the transmitter/receiver. So I already have the signals analyzed because I can use the IR led to send out the duplicated signal and it works just fine. If I need to analyze the signal further, will I only need to just wire it directly into the other device, or will I need something between them still?

 

[hexreader]

The receiver works much like a "gate" as you suggest (assuming you are using something like TSOPxx38 3 pin receiver chip). The transmitter will have 38KHz (or similar) carrier, modulated by the signal of interest, so connecting transmitter LED signal straight to microprocessor input is unlikely to work.

The receiver will give a low when 38KHz (or maybe 40KHz for Sony, 36KHz for RC5) IR is being received, and return to high (due to weak internal pull-up resistor) when nothing is received. There are minimum and maximum Mark times specified in the datasheet for your receiver.

If you are going microprocessor to microprocessor, there should be no problem - you can skip the 38KHz modulation part of the system.

Also be aware that the receiver signal will be a slightly distorted version of the original Tx signal. Mark tends to get shortened and space tends to get lengthened when using receiver chip.

 

[jesjohnson]

So it sounds like going microprocessor to microprocessor is the best way of approaching this problem and technically, that is what I was trying to do in the first place, I just thought using the IR signal input would be the easiest way to approach it. Unfortunately, I don't feel confident that I have the knowledge to manipulate the other microprocessor. How would I go about doing this? Is there any references I could research to help me do this?

 

[krazatchu]

Get yourself an Arduino, put an IR receiver on it (TFM5360 maybe) and use Ken Sheriff's IR remote library, it's easy as pie...
I used the same setup to capture some standard and proprietary IR signals from various camera remotes for a universal camera trigger project...
There are details on my blog here:
Michael--