Try the DalSemi 1-wire systems (www.dalsemi.com) they can be handled
with a single pin. I have some that are programmed via the 1-wire to
turn on and off a pin when the temp violates my limits (thermostat mode)
joe
Russell McMahon wrote:
>
> Octavio,
>
> From: Octavio Nogueira <nogueira@AJATO.COM.BR>
> >I'm developing a temperature controller with two sensors,
> >- I though of using  ....
> >Any other though?
> >The range is from 50F to 150F and need to be cheap.
>
> A cheap and "good" accuracy temperature sensor can be made at moderately low
> cost if you are prepared to allocate an analog input and a control pin.
> OR you could use it to drive a VCO and then use a digital ionput pin to read
> frequency.
>
> The voltage drop across a diode is related to its absolute temperature.
> A calibration factor is involved.
>
> BUT
>
> The difference in voltage drop across a diode at two known currents is also
> related to temperature and is independent of anything except the physical
> properties of the junction (ie - all silicon diodes give the same result). A
> practical circuit will involve a switchable current source and an amplifier.
> A quad package of low cost 324 opamps would very probably suffice for all
> the active electronics.
>
> I don't have a practical circuit to hand but various magazines have done
> devices based on this principal or you could derive it directly. Many
> libraries have collections of circuits in book form and these are nearly
> certain to include a practical circuit.
>
> I'm probably going to be doing something based on this in the next few
> months but not just yet.
>
>       Russell McMahon
> _____________________________
>
> >From another world - www.easttimor.com
>
> What can one man* do?
> Help the hungry at no cost to yourself!
> at  http://www.thehungersite.com/
>
> (* - or woman, child or internet enabled intelligent entity :-))