Measuring voltage from Thermoelectric generator

Projects General Guidance
1

Hello,

I am currently working on a project where I am measuring the amount of voltage produced from a thermoelectric generator, TEG, based on a small temperature difference. The voltage out of the TEG is very small, in the millivolt range and the arduino is having trouble reading the values. I am able to read the values from the arduino, but they tend to stick to the same values for a certain time until a significant change happens, so the voltage drop over a time period is not smooth. After a bit of research, it was concluded that I would need to incorporate an op amp so the voltage would be at desired levels to the arduino. I am pretty certain the op amp has the correct configuration so I think the problem is in my coding. Any help would be greatly appreciated as I am fairly new to using an arduino. And please let me know if i skimped out on any information. Thanks.

unsigned long time;
void setup() {
Serial.begin(9600);
Serial.println("Begin Recording Data");
delay(2000);
}

void loop()
{
time = millis();
float sensorValue = analogRead(A0);
sensorValue = (sensorValue/1023)*5;
Serial.print(sensorValue,6);
Serial.print(" Time: ");
Serial.println(time);
delay(500);

if (time >= 300000) // after 5 minutes the code prints done
{
delay(60000);
Serial.println("5 Minutes is up");
}
}

-Kenny

2

Did you measure the output voltage of the opamp with a DMM?

3

Suggest you print out the raw values from the analog read to see whether it's changing smoothly as you're expecting. This function returns an int, by the way, not a float. If you're looking at the raw value, it'd be best to treat it as an int.

4

I'm wondering how you have that wired, what your resistance to ground is.

5

That's a good pointer.

If the input impedance of the amp is too low, the signal will vanish. Especially when using the simple inverting amp. I think you can buy special instrumentation amps for these sensors.

6

Thank you all for your responses.

After measuring the op amp with a DMM I'm not sure it works any longer. I may have burned out one of the op amps, but just in case, I have included a picture of the layout of the op amps to make sure the wiring is actually correct. I modeled it on Multisim and it appears to be correct.

I also checked the raw values using the basic analog serial read example with the arduino and the values out we fairly smooth, but when using the an "int" instead of a "float" I don't get the precision needed to make a smooth graph for my project. Using the code from my first post, I have also included a picture of the graph from the data output of the arduino without using an op amp. I would like the curve to be smooth, and the expected output is supposed to decease exponentially. Any help is greatly appreciated.

7

The way you have wired up the power buses on the solderless breadboard looks very strange to me. But maybe it is time to have a nap.