A custom PID controller to automate the thermal processing (cleaning) of silicon samples in our Electron Spectroscopy Lab.
The electrical resistivity of silicon changes exponentially with temperature, making it challenging to control temperature manually with a fixed voltage or current. 
The brains of the project is an ESP32 S3 super mini. The controller measures the real-time voltage (with a voltage divider) and current (hall sensor) to calculate the delivered power.

The derivative term is physics based is designed to handle the unique electrical properties of silicon, which requires a high initial voltage to "fire up" the sample at room temperature before transitioning to a lower-voltage operating range when the sample heats up.

This whole setup is a prototype on a perforated board with some 3D printed case. You use the brown 10-turn potentiometers for power setpoint and programming the power curves - it can play-back predefined power setpoints in time.