Thanks Bob, this is a good input!
I'm not so able to manage a SOT-23 component..., altough I have seen on the PicList many useful methods for this. At the moment I would prefer to start with a "normal" transistor and see if the results are acceptable for my use.

regards
MarcoG

 


---------- Initial Header -----------
 
> Hi Marco,
> 
> If you stripped the circuit down to just the fundamentals, what you have
> is two transistors, a few resistors, and a comparator (inside the PIC).
> Make a free running loop alternately comparing the two transistors, and
> heating one of them. Try to keep the hot transistor hot(preprogrammed with
> the low-value resistor on the reference transistor) by watching switching
> of the comparator, and keep track of the timing for your intermediate
> result. Compare that value with a lookup table and you have it. Using a
> SOT-23 package transistor (not mounted to the circuit board) you should be
> able to get faster response.
> 
> You'd use three pins on the pic: two comparator inputs and another pin to
> drive the heated transistor.
> 
> Cheerful regards,
> 
> Bob
> 
> 
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