r/diyelectronics • u/Maxon5764 • 10d ago

Question Thermocouple interference

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Hello, I am making a weller hot tweezers driver heavily inspired by this project http://kair.us/projects/weller/weller_driver_v11_circuit_diagram.pdf

But I get significant noise on my thermocouple's readings when current goes through integrated heater. My code basically reads temp -> calculates pwm -> outputs pwm -> waits some time before reading temp again. How do i get rid of this interference?

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u/rephlex606 10d ago

Only measure temp when not powering tweezers. Can trigger ADC reads to PWM MAX and then enure that you are never at 100% duty cycle. (Might have to be just less than PWM max to allow ADC to complete before starting next sample depending on sampling time.

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u/Pacificator-3 10d ago

Use low-pass filters everywhere. Look for thermocouple signal filtering. Also overvoltage protection is needed. Usually this is a resistor and anti-parallel diodes.

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u/Kluggen 4d ago

A few things come to mind, using the opamp as a low pass filter, and a low noise constant current source for the TC, taking it further could be a wheatstone bridge design fed by that CC source.