Simulating a Thermocouple (redux)

Other Hardware General Electronics
1

Hi. There was a topic with this subject a couple of years ago, but it’s locked now, and it didn’t address what I’d like to do. Here’s the situation:

  1. For years I’ve used a CyberQ controller for my Kamado Joe smoker. It uses wired, plug-in thermocouples to manage the smoker temperature via a fan, and to monitor the temperature of up to three foods. It works quite well.

  2. Now I have several very advanced wireless thermocouples and Arduino code that can read them via Bluetooth.

  3. I’d like to eliminate the wires between the smoker and CyberQ by creating an Arduino interface to read a wireless thermocouple via BT, translate the reported temperature to the corresponding signal read by the CyberQ, and feed the signal to one of its thermocouple ports.

  4. I don’t know what type of thermocouples are used by the CyberQ (type K, type T, etc.), but I think I can figure that out by connecting them to a temperature probe readout device I have.

  5. I’ve seen published correspondence tables for temperature vs voltage for various thermocouple types, and know how to generate a PID voltage using PCM. Can the Arduino generate low enough voltage to simulate a thermocouple?

  6. I’m uncertain about how to connect one of the Arduino output ports to the CyberQ, primarily because I don’t know how thermocouple measurement circuits are designed. This is the part I really need help with.

Thanks for any advice.

2

Hello peppersass,

The output voltage of a thermocouple is quite low, and is likely to be a few 10s of millivolts or less at cooking temperatures.

To produce voltages in this range using an Arduino, you would use PWM to generate a voltage between 0V and 5V, and then use an attenuator to divide this voltage down to the correct range.

You would have to divide by some number to be determined, but this is likely to be between 200 and 500 to give voltages in the range of 0mV - 25mV or 0 - 10mV.

Can you give us more information about the equipment you have, such as model names or a link to the manual?

3

Hint most thermocouples have color coded wires. Here is a nice chart: https://assets.omega.com/landing-pages/colorcodes/tc_colorcodes.pdf I have used there equipment and litature have found it to be notly accurate but also very realiable. No association with omega, just a user.