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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Ir remotes
Date: Mon, 20 May 2024 04:07:24 -0700
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On 5/20/2024 2:50 AM, Lasse Langwadt wrote:
> On 5/20/24 09:15, Don Y wrote:
>> On 5/20/2024 12:01 AM, Don Y 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"?
>>
>> 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?
> 
> 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 

Yikes!

> because someone clever many decades ago thought to use an AM IF filter

If that is the case, then signaling an interrupt on each edge/cycle
would obviously kill a linux kernel (I've handled 140KHz interrupts
but 455KHz would really be an annoyance)  50KHz would be a piece of cake.

Thanks.  I should be able to verify this by looking to see what sort
of B&O devices are (or are NOT) supported.