A very simple controller with a light electronic BoM. It manages the fridge temperature with hardcoded thresholds and hysteresis.
The board is powered by a PIC12F683 MCU. It samples the fridge or freezer temperature through a NTC sensor. It then controls the fridge cold unit through a 230V/12A relay.
The board schematic and PCB are designed with KiCad 6.
The microcontroller firmware is compiled with the free version of Microchip XC8 compiler.
Naked PCB :
Assembled PCB :
Connector adapters for the targeted freezer :
Transparent plastic casing (reference Deltron 479-0160-0) :
Board inside the casing with drilled holes and connector adapters :
The board controlling the freezer in a basement :
The following information have been found through reverse engineering, so be careful about their accuracy !
The picture below shows the connector names (the names are taken from the original controller board PCB).
There were no indications on the PCB of the pin numbers, so I assigned them myself.
Connector CN1 signals :
| Pin number | Description |
|---|---|
| 1 | Not connected |
| 2 | Not connected |
| 3 | Original controller GND |
| 4 | NTC (thermal sensor) |
Connector CN2 signals :
| Pin number | Description |
|---|---|
| 1 | Cold unit (note 1) |
| 2 | Cold unit (note 1) |
| 3 | Not connected |
| 4 | Not connected |
| 5 | Door switch (note 2) |
| 6 | 230V neutral |
| 7 | Door switch (note 3) |
| 8 | 230V live |
Notes :
- Connect CN2 pins 1 and 2 to neutral to start the cold unit.
- Door switch contact is normally closed.
- CN2 pin 7 is connected the 230V live on the original controller board.
Connector CN3 is not populated.