piclist 2001\04\06\135352a >
Thread: IR protocols
www.piclist.com/techref/microchip/ios.htm?key=ir
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face BY : David Cary email (remove spam text)



Dear Wan Hasmi,

Wan Hasmi <@spam@whasmiTakeThisOuTspamVISCON.PO.MY> on 2001-04-05 08:20:53 PM wondered:

> Subject:     Re: [PIC]: Sample serial data
...
> I connect the output from the IR module to one of the PIC
> I/O pin and monitor the pulse
...
> how do we differentiate which key was pressed if we sample
> the I/O pin on PIC?
...

There's a lot of links to IR communcation protocols (and a few schematics) at
 rdrop.com/~cary/html/machine_vision.html#communication
 ftp://ftp.armory.com/pub/user/rstevew/IR/
.

Most cheap "TV remotes" transmit a ``1'' by turning on and off the LED at 40
KHZ, and transmit a ``0'' by keeping it turned off.
They send bits at about 2 Kbit/s. If you have the right hardware to "demodulate"
the 40 KHz signal, your PIC only needs to sample at maybe 4000 samples/s (is
that right ?).

Once you press a button on a remote, it keeps sending out the same bit pattern
over and over until you let it up. Some of them alternate between 2 different
bit patterns for the same button -- so that when you hold down the "channel up"
button, the TV goes up only one channel, until you release and press it again,
giving the *other* channel up code that allows the TV to go to the next channel.

(Um, does this need to move to the [EE]: topic ?)

--
David Cary

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