I am designing an at-home PCR machine for COVID-19 testing, and the machine needs to heat the sample to three different temperatures precisely and quickly (95 C, 60 C, an 75 C). I have tried using the Adafruit AD8495 thermocouple amplifier with type K thermocouple wire integrated with the Arduino. I followed the instructions on soldering and connecting the board exactly as described in this link:
The only difference is I am using an Arduino Uno board. However, when I copied and pasted the code after wiring, the output is showing an unchanging 177 C. Unplugging the thermocouple wire did nothing to change the value, it seems to stay the same independent of the Thermocouple wire status. I have tried the following de-bugging techniques:
Unplugged the thermocouple wire - no effect.
told the output to display the return voltage, which was an unchanging 2.14 V.
Changed the input voltage pin to 5 V. In this case, the value changed to a constant T = 739 C and V = 4.95. It still remained independent of the Thermocouple wire connectivity
Changed the wire that goes to ground - no effect.
Ensured the thermocouple wire was completely stripped of the insulation at the terminal end, so there was only metal going into the connection ports - no effect.
I don't know what diagnosis to make from this data, however. It seemed like my solder joints were sufficient, but perhaps I accidentally shorted out the board?
I am considering a backup plan of using a thermistor instead since it seems simpler, more robust, and more precise. Especially since my device will not exceed 100 C. Beyond this initial question, are there any thermistors you can recommend?
Thanks in advance! I hope I told you enough for this question to be useful.