Proofing Box V2
7th August 2022
An updated version of my temperature controlled proofing box

My initial proofing box was an important part of getting consistent results when baking bread but it stopped working rather mysteriously while I was out of town in 2018. That version was built on a Raspberry Pi, had an integrated webcam, and recorded timelapse movies of bread rising. As cool as all that was, it was a giant pain to manage and troubleshoot. Since it was running linux much of the work of maintaining it was effectively system administration, which is not a task I enjoy.

So when it came time to rebuild I decided to go with a much simpler design. This new version is built around an Adafruit Feather M0 Bluefruit LE that I happened to already have. It lacks any kind of network awareness (I’m not using the bluetooth at all) but it does have a bright OLED display and physical controls, making it perfect for my needs.

The electronics are modular, built around the Feather spec, so that the display, power electronics, and microcontroller can each simply be unplugged and removed for maintenance or replacement. The power electronics module is responsible for providing 5V to the microcontroller and switching 12V to the heaters in response to a PWM signal from the microcontroller.

OLED display showing a sample screen layout with temperature, set point, and a graph
An early test of the display
A proto board in the feather form factor with mounted electronics and wires leading to barrel sockets
The power electronics module fully assembled
A stack of feather modules sitting on a test bench
The power electronics and screen modules sitting on top of the microcontroller for an early test
The electronics modules in test configuration, attached to a bench power supply and an oscilloscope displaying a pair of square waves
Verifying the PWM switching on the test bench
A close up of an oscilloscope displaying a pair of square waves
It's so convenient being able to directly examine the switching behavior
Circuit boards on a test bench connected to flat yellow heaters and a temperature sensor
First heater test. The screen shows an older version of the final display.
Circuit boards on a test bench with wires going into a gray foam box
First assembled test to evaluate response times
A plastic project box with a clear face. A switch, a red button, a blue button, and a screen are mounted to the front of the box
The final electronics mounted in their project box
A plastic project box with a clear face. A switch, a red button, a blue button, and a screen are mounted to the front of the box
The electronics enclosure in place with the proofing box. The screen shows the final display layout

I let this project burn in for several months before finally mounting everything into a project box. Having real buttons and a power switch feels like a giant luxury after dealing with the tiny buttons on the OLED and pulling the plug to turn it off.

Hopefully this revision lasts a good long time and I won’t need to update it until I finally decide to build a proper box (if I ever do - foam has its advantages).