> Thinking about the OpAmp solution, wouldn't a comparator be even 
> better/more
> suited to my application?
> LM339 quad would do the trick, (or rather a pair of them - I need 5
> comparators - bugger!)
>
> I assume the LM339 can switch at 1kHz comfortably?

LM339 is a technically superior solution BUT, unlike the L:M324 which drives 
high actively, all its comparators are "open collector" output so need a 
pullup resistor. using Dave Minklers suggestion of using pullups on the PIC 
you could do it with no external pullups.

> You mention a decoupling capacitor on the supply.  I am using an LM317LZ 
> vreg
> to provide regulated 5v, from a 12v DC input (& another for 1.5v) for PIC 
> and
> possibly now the LM339, which has a 0.1uF(IIRC) capacitor on the output
> already - so will I still need a further decoupling capacitor for the IC?

A 0.1 uF for each IC between its power supply pins is usually a  good idea. 
Not always essential - but it's a shame to have things fail due to excessive 
noise for want of a cap worth a few cents.


        RM

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