> Ok guess Jpgs aren't allowed...

It's not a big one, should've got through

> http://www.gavin-egan.com/thermistor.jpg

As I understand it, you want to emulate this function of the
Ferranti IC, not the operation. In which case a 10k
thermistor should be an OK source for the PIC's ADC,
particularly in the resistance range you're interested in. Have
the thermistor as one R in a divider, something like

5V --- thermistor --- ADC pin --- R + C --- 0V

You could buffer the divider with an op-amp but the
impedance is going to be low enough for reasonable
results. If you want to concentrate on a particular region
of resistance, then buffer/amplify/level shift to expand that
voltage window. For example, you could arrange that
resistance from 10k to 2k is clipped to 0V or 5V and
only below 2k does voltage output change

> Its also funny how looking at this and talking about it
> on email has made me come up a couple of thoughts

I told somebody exactly that the other day. Explaining
a problem makes you think it through and see things you
hadn't previously.

She did, and she saw. Like magic it was, very gratifying

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