I needed a safe way to process high-temperature engineering filaments for Baja SAE without contaminating food appliances, so I built a dedicated low-cost annealing oven from a used toaster oven and basic control electronics.
Hardware Architecture
The system uses an Arduino, high-temperature thermistor, and solid-state relay. Rather than fully gutting the oven, I routed the AC feed through the relay so the controller can regulate heater power while preserving the original heating hardware.
Control Loop Strategy
The Arduino continuously reads chamber temperature and drives the relay using a PID loop. Proportional handles present error, integral compensates accumulated offset, and derivative damps overshoot by reacting to rate-of-change.
Why PID Instead of On/Off
Compared to bang-bang control, PID gives smoother heater modulation near setpoint. That reduces temperature swing and prevents large thermal overshoots, which is important for repeatable material processing.
Performance
Current tuning holds chamber stability to roughly plus or minus 3 degrees Celsius, which is good enough for current part workflows and already much better than manual or simple thermostat operation.
Next Revision Plans
Next steps are sensor averaging for smoother feedback, deeper PID tuning passes, and adding an onboard LCD interface so live process data is visible without a tethered laptop.