A hot-process timer for the stove. It watches the pot and tells you, on its own face, whether you are still inside the window you meant to hold.
Hot-process cooking — hot sauce, soap, preserves, confectionery — lives or dies on holding a temperature band for a set length of time. Miss the band and you have either not finished the process or ruined it, and you usually find out later. A probe thermometer tells you the temperature right now; it does not tell you whether the cycle is going well.
So the Sentinel holds both. A K-type thermocouple reads the pot, the display shows the safe range you are aiming for, and the device tracks whether you have stayed in it for long enough. When the cycle is satisfied it says COMPLETED, and it says it from across the kitchen rather than from a screen you have to pick up. A keyswitch arms it, so it cannot be started or stopped by a wet elbow.
Built from
- Particle Photon 2
- K-type thermocouple with MAX6675 amplifier
- Grove 0.66″ OLED (SSD1306)
- BME280 for ambient temperature, humidity and pressure
- SPST keyswitch to arm, DPST power switch
- 5 mm green status LED with 220 Ω resistor
- 3D-printed enclosure and probe stand
Read the full build on Hackster →
Photographed in the kitchen with Mike, in his CNM Culinary Arts whites.
Particle Photon 2 · thermocouple · 3D-printed housing · 2026