Re: Re-using IR Decoder Chip

[Just Another Joe <address@xxxxxxx>]

On Sun, 24 Dec 2006 03:08:34 GMT, nobody@xxxxxxxxxxxx (Dave Houston)
wrote in message <458de98b.736604421@xxxxxxxxxxxxx>:

> Just Another Joe <address@xxxxxxx> wrote:
>
> >Okay then, how about a purchased IR decoder chip, for example for a NEC
> >protocol?  They should be fairly cheap.  That should ease the load on
> >the cpu.
>
> I'm not sure what it is you are trying to accomplish. Decoder chips for
> specific protocols went out of style about 20 years ago. A NEC decoder is
> only useful for the NEC protocol and any microprocessor can do the same job
> as well as handle other protocols.
>
> IR receivers like the [optional] TSOP1100 used in roZetta handle carriers
> from 33-57kHz and output the demodulated data envelope. The most widely used
> IR protocols are fairly easy to distinguish and decode - there's little
> processing involved. And, you really do not need to decode - as long as you
> can output a unique code that is consistent for the specific sequence of IR
> (or RF bursts) you can use that to trigger consistent responses.
>
> Less widely used IR and RF protocols (there are thousands) are not so easily
> handled as far as decoding but nothing you propose changes that.
>
> Maybe an example will help. The snake-oil purveyors (Pay no attention to
> that fishy looking fellow behind the curtain.) pushing Z-Wave make much ado
> about it using DES encryption. I don't give a fig about the protocol or
> about how it might be encrypted. I can capture a transmission and play it
> back and it will have the same effect every time regardless of the protocol
> and regardless of any method of encryption. The encryption does nothing
> other than prevent neighboring systems from controlling your system - it
> doesn't take DES encryption to do accomplish that.

Okay, perhaps I'm misunderstanding how roZetta will capture IR.  I took
it that the cpu would 'watch' a particular pin for transitions from the
IR indicating ones and zeros until a byte was accumulated, rather like
capturing serial bits and bytes.  The timing and decoding would need to
be adjusted for each IR frequency and protocol.

Now, I've seen IR decoder chips which do the capture, and simply present
a byte representing the code to a serial port.  That is what I meant by
easing the load on the cpu.  This would be rather like using a W800RF32
to decode RF and simply present bytes to a serial port.  But, if it
doesn't provide any real advantage with the IR, that's okay.  It was
only an idea.

--
Just Another Joe        Remove .windows to reply.
Why be politically correct, when you can be right?