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NNTP-Posting-Date: Mon, 20 May 2024 13:41:29 +0000
From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: Ir remotes
Date: Mon, 20 May 2024 06:41:28 -0700
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On Mon, 20 May 2024 00:01:18 -0700, Don Y
<blockedofcourse@foo.invalid> wrote:

>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]

If the IR link is DC-coupled, namely all digital, there is the
thresholding problem. If a photodiode converts light to voltage and
that drives a comparator or equivalent, where should one set the
threshold? What happens when the room light is bigger than the
received light from the remote (which it often is) ? How does one
handle, say, a 1000:1 receive power range?

A tuned front-end dances around these problems.

A mostly-digital receiver would use a fast ADC to digitize the
photodiode output and apply a LOT of DSP horespower. FFTs and such.

Have you researched the actual optical waveforms that remotes make?
There's tons of stuff online, and it might be fun to measure some too.