Stefan, are you saying connecting a Type J (or K) Thermocouple direct to an analog input pin using a PIC12F683? What about a AVR chip such as a ATmega168 or similar? Perhaps using the internal 1.1 reference voltage? I wasn't sure the analog input would be sensitive enough to read the low mV of a thermocouple.
Thanks for any input.
Ken H>
--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
>
> In this kind of application it is often acceptable to work without
> cold junction compensation. (Room temperature variations would be
> inside acceptable temperature error). That way you could avoid the
> costly AD595.
>
> Another alternative would be to use a thermistor instead, one suitable
> for this temperature could be found in every laser printer at the
> fuser roller.
>
> ST
>
> On Sat, Dec 26, 2009 at 6:34 PM, rdheiliger <rdheiliger@...> wrote:
> > I have modified my PIC based temperature control to use a K thermocouple instead of a LM34. I used an AD595 chip to linearize K thermocouples to 10 mV/∗C. This is a simple circuit using a PIC12F683 for analog input and a PWM output to a digital panel meter for display of temperature and set point. Two switches are use to set the temperature. Normaly the temperature is displayed. When either the increment or decrement switch is pressed the unit displays the set point and allows it to be changed. A relay with on/off control keeps the overshoot to less than 8 degrees C.
> >
> > I changed to thermocouple input when i needed temperatures in the 160 ∗C + range.
> >
> > The AD595 and K thermocouple can be obtained from Spark Fun Electronics. Tho not cheap.
> >
> > RD
> >
> >
> >
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