I have a challenge that I would like to share with you. (at least a challenge for me)
The resistor R8 (10 turn potentiometer) can be adjusted from ~0 to 1K Ohm to output voltages from 3mv to 30mv. The divider labeled (400F) outputs constant 8.3mv that equals 400ºF for a K Type Thermocouple. All that worked great.
So later I decided to add a fancy LED (D2). The LED should turn ON when the temperature is above 400F and OFF when below. I suspect using a LM741 as a comparator is a poor design because of precision and low voltages. One option would be an AD790 comparator http://www.analog.com/static/imported-files/data_sheets/AD790.pdf A comparator in the .25mv offest range would be suficient for the precision I need.
Is there a simpler (cheaper) way to achieve this with precision and low voltage in mind?
*UPDATE - HERE IS THE FINAL DESIGN http://iddevlabs.blogspot.com/2014/09/diy-thermocouple-testing-circuit.html