Hi Andrew,

On Saturday 17 April 2004 15:43, Andrew Kilpatrick wrote:
> I've played around with this a bit. You need to read not only
> the presence of a pulse, but decode the pulse train as well.
> Most of the receivers I've seen put out the data output with
> the carrier removed. This means that either you need to write
> your software with the timing for a specific model of remote,
> or you need to have some way of teaching the PIC. (like a
> learning remote) The former is probably the best way to start.

Yeah, that was my plan. I might do the learning thing later as that
will give me chance to learn how to use the EEPROM space too in
order to store the learned codes in.

> If you find specs on the web, it will let you write receiving
> code without much trial and error. I made a PIC send codes to
> my CD player, and the data format was very simple. It was just
> two bytes, the first being the actual command byte, and the
> second being the retrograde (bits changed MSB to LSB first, or
> whatever) of the byte as a checksum.

Ah, I hadn't realised they had checksums and things... useful to
know.

> The data rates are usually very low (1000bps) because the
> carrier is only around 40khz. You'll find that some buttons on
> the remote, such as volume and channel, send the code repeating
> over and over, obviously so you can hold down the button. The
> repetitions are usually fast enough to trigger a scope. You can
> usually fit the entire message on the screen at once. This will
> give you a really good idea of what sort of timing you're working
> with.

I've been wondering how long it will be before I have to get around
to buying a scope :-) And learning how to use it for that matter...
pity they are so expensive though :-( I might see if I can pick up
a second hand one on ebay...

Thanks for all the info, very useful.
Matt

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Matt N. Marsh
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