I have a sensor (k type thermocouple), the output ranges from 0 to 55 millivolts.
On the thermocouple I connect the cathode to ground and the anode to an analog in pin, then do a simple analogRead() on that pin and direct the reading to the serial monitor. (I think this is correct?)
Anyway, it reads nothing but 0. (when I disconnect the Thermocouple, it reads random values for signal noise, but when I hook up the TC...it drops back to 0,0,0,0)
I think this is because at room temp, the output is in the 1-2 millivolt range...and that is too small for analogRead to pick up?
Is there some way to configure the arduino to accurately read voltages in the 0-55 millivolt range?
(I'm trying to avoid using a max amplifier chip if I can)
reads noise at first, till i hook up the TC, then drops to 0
805.00000
947.00000
578.00000
780.00000
523.00000
467.00000
816.00000
475.00000
632.00000
0.00000 <<here is where I connect thermocouple
0.00000
0.00000
0.00000
0.00000
0.00000
RuggedCircuits:
You really need a thermocouple amplifier.
yeah...well if it comes to that I'll use the MAX6675, but the freaking thing is $12 bucks and its only available in SMT. I'mn pretty bad at regular through hole soldering...let alone SMT. (the 6675 on a breakout board is over $20)
I was really just trying to crudely replicate the functionality of the max chip using code instead of the chip. I can use a thermistor for the cold junction compensation reading.
I know it won't be as accurate as with the chip...I'm just wanting to figure out how accurate I can get using code and a thermistor ($1) instead of the max chip ($12)
I could do average of readings over time to mitigate the noise readings...
3z33:
I might need some help selecting the op amps, the first one (A1) is a special low noise amp (probably one of the maxim-ic products)
I've had some success with LT1007 and LT1037 amps. But the MCP3424 ADC works better, IMO, than the analog approach. The MCP9800 is a nice I2C temperature sensor to use for cold junction compensation.
The open source libraries for the TC4 project include one for type K linearization.
If you use the MAX6675 be very cautious about the effects of self heating on it's CJC results. Test with a loop of copper wire in place of the thermocouple and watch the reading rise for several seconds right after power up.