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'12C508 as a Holtek HT12 Encoder?'
1998\02\11@154553 by Mark Winters

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Hello All,

I'm trying to program a 12C508 to emulate a Holtek HT12A encoder to send an IR
signal. (For those not familiar with this chip, it repeatedly puts out a
signal consisting of 12 bits on a 38kHz carrier).

To make a long story short, the program I've written to do this isn't working
correclty, and it's making me wonder if I'm my assumption about the data
transmission rate of the Holtek chip is incorrect. In looking at the Holtek
data sheet, it appears that using the "normal" circuit configuration would
result in a data rate of 1 bit per 1ms (with a "one" represented by a 333uS
burst, a "zero" by a 666uS burst).

For those that are familiar with the Holtek chip, does this sound correct? I
don't have a scope (sigh!), but if I put a visible-light LED on the output of
the IR receiver module I can see a visible "flicker" when using the Holtek
chip to transmit. With my program running on the 12C508, however, the flicker
is much less noticable, making me wonder if I'm trying to send the bits too
fast (and yes, I am sending the12 bit "zero" header with a start bit in the
last bit of the header before transmitting each 12-bit word).

Any ideas?

Mark Winters

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