A proportional-integral-derivative (PID) controller is a control-loop mechanism that employs feedback to match a setpoint for applications that require constant modulated control, such as precision temperature, industrial pneumatics, making beer, and other platforms that require feedback information. Those over at Bread and Bullets designed its DIY Universal PID Temperature Controller for proofing sourdough bread and driving a 1400W toaster oven for powder-coating bullets during a reload process.
B&B created the Universal PID Controller using an inexpensive Inkbird unit with integrated heatsink, a 40A SSR, thermocouple, 15A fuse holder, and 10A slow-burn fuses, as well as various other parts, including a 10A plug adapter, power switch, and connectors. All of the hardware sits inside a laser-cut wooden enclosure, painted silver to provide an industrial aesthetic and protects it from moisture. B&B did mill an acrylic enclosure but decided to stick with wood for this project.
With all the parts assembled and the PID controller configured, B&B then did a hot water test to make sure everything is operating correctly before tasking the controller for regular use. The how water test is just that, a saucepan is filled with water, which sits on a hot plate. A thermocouple is affixed to the saucepan via a butterfly clip, while the hot plate is connected to the controller. The desired temperature is set, and the controller adjusts the hot plate to maintain that temperature.
The DIY Universal PID Temperature Controller's overall design is simple enough that anyone can recreate and cheap enough to get most of the parts at your local hardware store. B&B uploaded a detailed walkthrough on their project page.