Ir remotes

May 20, 2024 3 Replies
D

My understanding is that Ir remotes modulate an Ir "carrier" signal in a particular pattern to express a particular "code" corresponding to the key pressed/held.



And, that different "chipsets" use different carriers and encodings.



Is there a front-end that is tuned to the particular carrier in the receiver? Or, is all of this done "digitally"?



I.e., with a fast-enough (Ir) photodetector, should I be able to decode ANY signal from ANY "remote"?



Said another way, is the fact that a particular device ONLY recognizes a particular remote related to its use of a particular chipset (or, equivalently, decoding algorithm in software)?



[The former would be hard to change but the latter should be relatively easy]
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D

And, before anyone mentions the obvious, I've already looked at lircd which is the reason behind this post; why do they claim they can handle ALMOST all remotes? Is this a limitation of their hardware implementation? Or, timing problems in the way they try to process the raw video signal?

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L

afaik almost all use a 30-50kHz carrier, nominally something like 38kHz, I think the common IR receivers have build in bandpass filter, so it is just a matter of interpreting bits (there's a few common protocols)

I know that B&O (used to?) be an exception with a 455kHz carrier, I'm guessing because someone clever many decades ago thought to use an AM IF filter

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M

Yes, its modulated as others pointed out. I think the Philips protocol is the most common. Played with decoding a hauppauge remote years ago. I think there's a preamble to set the timing for 1 and 0, then the data follows. Pretty simple.

Cheers

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