Morgan Olsson wrote:

> Or use an 8pin PIC with internal osc...
> But the 555 is stronger driver and higher voltage.

  Only to ground.  A major problem with the NE555 is that it doesn't
pull up to the positive rail, but rather a volt or two short (it is TTL-
based).

  Amongst other things, this makes it difficult to obtain symmetrical
square waves (if that is what you want) even using the one-resistor mode
and correspondingly inaccurate in this mode.

  If you do want accuracy in one-resistor mode, you use a TLC555 (CMOS
version) but this is then *NOT* as strong a driver as a PIC.

  It's unlikely a 12C508 will be anywhere near as cheap as a NE555,
but it may rival a TLC555.  It's internal R-C oscillator is probably
not as accurate over temperature as a TLC555 either, but it is certainly
more compact (no external components at all), and way more elegant/
versatile.

  Put a crystal (cheap) and two caps on it and it's *far* more accurate.
--
  Cheers,
        Paul B.