Minimum analog voltage

[Shohadawy]

What is the minimum analog voltage that the pic16f877 can sense??... can it sense the small voltages that a thermocouple produce ( 0-7 mv)

 

[dknguyen]

THe minimum voltage it can sense is:

(ADC Reference Voltage)/(2^n) where n is the number of bits the ADC has.

So at 5V, the minimum a 10-bit ADC can detect is 5/4096 = 4.88 mV.

So no. Also, remember the thermocouple can output NEGATIVE voltages at certain temperatures so if it's measuring cold your PIC won't work either (and may be damaged). You need a very large gain, very quiet, differential amplifier that may need to be bipolar (depending on the temperature you are going to encounter).

See your other post. I explained it more there.

 

[Shohadawy]

Thank you very much for your reply

 

[Diver300]

I agree that a PIC cannot measure a thermocouple with any realistic accuracy.

However, a thermocouple won't damage a PIC when the signal goes negative. The absolute maximum signals for a 16F877A is -0.3 V or -20 mA. You won't get either of those figures out of a thermocouple.

 

[Shohadawy]

Thank you Eng. Diver