Re: 40kHz Infrared Serial Modulation?

If you are using a UART on a micro controller, you can use software Manchester encoding of the packet to ensure no long runs of "1" occur.

I used the PWM output to produce a square wave (38kHz) sent continuously
to a 4066 input. The TX data then enabled the switch each time a "1" occurred.

To ensure you receiving UART locks on to the signal send a header that ensures synchronization. Some preamble (0x55, 0x55 ...) followed by a sequence that ensures UART sync (0x33,0xcc,0x33,0xcc,0x33) then your data and checksum. (data and checksum are in Manchester format).

If you check out the 0x33,0xcc combination, you will find that the Uart will always be in synch before the last byte .

Your receiver algorithm then waits for either 33 or CC to be received. It then waits for a none CC or 33 to be received (this is first byte of data).

You send each byte a nibble at a time by taking each bit in your data word and transforming it to a "10: if the original bit was a "1" and a "01" if it was a "0". The maximum length of "1" or "0" you can now have is 2 bit periods.

--

Kind Regards

David Huisman
General Manager
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Rich Grise wrote: 
On Tue, 17 Jan 2006 11:21:09 +1300, Terry Given wrote:


Rich Grise wrote:

On Thu, 12 Jan 2006 16:41:49 -0800, redbrickhat wrote:



In the Vishay TSOP32138 data*** the Data Formats are for IR remote
controls. Do you think that such an IR receiver could also handle
RS-232 data?

For example, in the link below, the TX pin of a PIC's UART is NANDed
directly to a 38kHz signal:

http://www.rentron.com/Infrared_Communication.htm

Wouldn't there be some problems with timing if the RS-232 data had a
long line of "1" bits? 



"RS-232 data" can't have "a long line of '1' bits". An asynchronous
data stream has start bits and stop bits, which if the thing isn't
terribly out of tolerance, will resynchronize on every character.

And, technically, "RS-232" defines signal levels and connectors,
and doesn't say much, if anything, IIRC, about the data format.

Here's a lucky google hit:
http://www.anotherurl.com/library/rs232.htm

Hope This Helps!
Rich



wot Rich said.

Hi Rich.

Cheers
Terry



Hi!

How was your holiday? Mine was wonderful - I sat at home and didn't have
to talk to any relatives. ;-P

Cheers!
Rich


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