> Suppose that for the sake of miniaturization, I want to receive
> a typical IR remote control signal (~35kHz carrier, on/off modulated
> with minimum on/off times on the order of 1ms) using a bare photodiode
> running into a PIC A-D converter (or similar) and doing all the signal
> processing in software.  It seems like that should be about possible.

I would have thought a PIC would be pushing it to deal with 35kHz into the 
A/D, although it may be possible with a DSPic I guess. But as others pointed 
out, the level straight out of a photo diode is pretty small, so you may as 
well amplify it with a bandpass amp at 35kHz.

> The signal I receive at the A-D is going to be a sum of ambient
> illumination plus noise sources (60Hz illumination, mostly) plus
> the signal I'm actually interested in.  Plus maybe other competing
> signals at slightly different carrier frequencies that I'd rather
> not see...
>
> 1) If I know the carrier frequency I'm interested in, and I know
>    that I'm interested in on/off modulation, how do I pick the
>    minimum sample frequency I can get away with?  Presumably I
>    don't want an exact multiple of the carrier frequency.
>
> 2) Does anyone care to point to a suitable DSP algorithm, hopefully
>    implementable on a typical integer microcontroller, that will do
>    the rest of the work I'm interested in?  This IS the sort of
>    thing that DSP algorithms can do, right?  If I need multiplies
>    and divides, can I pick a carrier frequency so that those end
>    up being shifts?

Personally I would have used an external PLL such as a CD4046 to detect the 
presence of the signal. I guess to do it in a DSP, the trick would be to 
implement a similar PLL arrangement. 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist