Hi Bob,

    Typical IR format,

        [Leader Code][Custom Code][Custom Code][Data Code][Data Code Negate]

    The Leader Code is used to indicate the start, typically
    a 8T high followed by 8T low.

    For the rest of the codes, for logic '1': 1T high, 3T low
    for logic '0': 1T high, 1T low, 1T high, 1T low.

    The Custom Code is to differentiate between equipments, its
    repeated for simple checking.

    The Data Code is the actual key code.
    The negated Data Code is used to verify the key code.
    Just XOR them and check for 0.

    You also need to modulate the logic signals with a
    carrier before sending it to the IR LEDs. The receiver
    must be selected having a bandpass filter centered around
    you modulation frequency.

    Say f = oscillation frequency, typically 455kHz
    Then, T = 256/f
    Modulation frequency, fm = f/12 (typically 37.9kHz at 1/3 duty)

    To save transmission power on continuous key press,
    you just need to send the Leader Code and a single
    complement of the Custom Code.
    The receiver end should keep a history of the last Data/Key code
    and repeat the command.

Regards,
Peter Tiang


----- Original Message -----
From: "Bob Bullock" <bobb@PROSTYLE.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, March 23, 2000 6:03 AM
Subject: [OT]What encoding scheme is used by common IR remote controls


> I'm starting a project which will involve two PIC's talking to each other
> using infrared.  I decided to have a look at what encoding scheme some
> common household remotes used, by Sony radio for example.  Feeding the
> output from my IR decoder into my scope, I would say it appears to be a
> Biphase scheme such as Manchester, but I haven't been able to be certain
> about it.
>
> Also any other clues as to any leading preamble bits or error detection
bits?
>
> Thanks
>
>
> Bob Bullock
> President
> Western Support Group Ltd.
> bobb@prostyle.com
> Certified Microchip Consultants
> http://www.microchip.com/10/Consult/Country/Canada/index6.htm#915-277
>