Re: Re-using IR Decoder Chip

[nobody@xxxxxxxxxxxx (Dave Houston)]

Just Another Joe <address@xxxxxxx> wrote:

>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.

roZetta will capture IR in the same manner as the ocelot captures IR except
the TSOP1100 handles a wider range of carriers (33-57kHz) than the TSOP1138
used in the Ocelot (38kHz).

When the Ocelot "learns" an IR code it merely stores an image of the data
envelope in memory. When it later receives a code it compares the received
data envelope with those it has stored. The elegance of the system is that
such brute force methods give results that seem quite a bit more
sophisticated than they really are.

roZetta will only handle the X-10 IR protocol plus the extensions that Laser
Systems developed a few years ago. roZetta does not attempt to decode other
IR protocols (although it will output hex codes for the NEC protocol since
it's the same as the X-10 RF protocol). And, the IR and RF receivers use the
same input pin so they are mutually exclusive.

>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.

The device you mention copied what I did with the BX24-AHT except they did
not realize that I was doing some decoding internally and making some logic
decisions before outputting the hex codes. The hex code output is inadequate
to fully discriminate between various types of X-10 RF codes.

Now, I have tried repeatedly to shift these discussions to the roZetta Yahoo
group since it is rather specifically about roZetta. I will not respond
further here.

http://davehouston.net
http://tech.groups.yahoo.com/group/roZetta/
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