Symptoms : when the Fridge tries to fire the compressor up, sometimes it works, some times it fails with the green temperature light blinking. It may succeed in starting the compressor but after 2-10 seconds, the compressors stops with the led blinking one time. It will try to restart the compressor after about 6 seconds.
This instructable will led you to a :
- fully operational fridge (that was the original and main goal !)
- with additional customizable features (like possibly negative temperatures in the fridge compartment :)
- optionnally connected fridge :
- follow the temperature remotely
- set temperature remotely
- failure monitoring/notification : overheat, malfunction, ...
This instructable can probably be used for any other microprocessor-controlled fridge.
Step 1: Salvage Components From the Old Board
The control board (labelled "Diehl 5 700 00 9456 KSV / VDE 702590-00 5199") is located behind the top front panel (behind the leds and the buttons). You can remove it after removing the plastic pins on the left and right of the cover.
- buttons (see location on picture)
- SMD leds (see location on picture)
- SMD resistors (3 x 12k7 for sensors voltage dividers, some 1500 for the leds) (see location on picture)
Markings on the smd resistors are described here :
- sensors connector
- power connector
WARNING : the use of a soldering station with hot air gun is mandatory for SMD components. You may remove the resistors successfully with a traditional soldering iron but you will destroy the leds)
Step 2: Gather Additional Components
ACS712 current sensor (optional but safer)
Some usual resistors/capacitors/diodes. I used SMD components salvaged from old electronic devices.
5v power supply (less than 1 amp is more than enough)
PCB tools : soldering iron, chemicals, ...
Components salvaged earlier from the old board
Motherboard spacers and insulation plastic sheet for final assembly
Install KiCad to print the PCB
Optionnally have a local server running openhab and mosquitto (or another mqtt server) to add connected features
Step 3: Check and Identify Pins
Check the problem on the fridge is only due to the control board
On the sensors connector :
There are three temperature sensors on this fridge :
- The first one is located behind the top front panel on the left when facing the fridge (small cylinder, white plastic, see picture) and is meant to measure the ambient temperature
- The second one is inside the fridge compartment, at the bottom of the right panel
- The third one, I don't know :) May be just before the freezer compartment but I was unable to understand the temperature curves I got from it.
With a multimeter, check resistance between blue wire (common to all resistors) and each one of the three other wires (yellow/brown). You should read something like 25k around 15°C. More if it is colder, less if warmer. On the ambient temp, you can check resistance increases if you warm the sensorwith your hand.
On the power connector :
- check the blue wire is connected to the blue wire on the compressor where the power cable is attached
- check the brown wire is connected to the brown wire on the compressor where the power cable is attached
You will use these first two wires to power the power supply
- With the multimeter, identify the correct black wire which is connected on the compressor : there are two black wires coming to the control board : the one you want is connected to the compressor : the relay will connect it to the phase to start the fridge. I don't know what the second black wire was used for. Let's call the first wire "compressor wire".
Once identified, it's time to check the compressor is ok :
- Unplug everything, especially the fridge from the fridge wall outlet.
- Switch off the corresponding electrical circuit of your house
- Connect the compressor wire to thephase (brown wire of the control board) safely : it must not bee too loose.
- Isolate the connection with electrical tape
- Check again the electrical circuit is off (with the multimeter, no significant voltage available at the outlet pins)
- Plug the fridge to the wall outlet
- Switch the circuit on
The compressor should start : wait a little bit (some minutes) to check the freezer compartment gets colder.
Step 4: Make the PCB
There are two boards which will be assembled together (and with the power supply and esp8266) with motherboards spacers.
Notes on schematic/PCB :
- An ACS712 is shown but I don't use it yet. It may be placed in an inaccurate location (near the relay and thus may be unusable)
- ... to be continued
Tell me if you need more information.
Step 5: Software Part
The software part features:
- remote monitoring of fridge state and temperatures via MQTT
- remote control of target temperature, super-fridge/supercooler modes and fridge state (off, standby) via MQTT
- wireless configuration to adapt configuration to your network/MQTT server
Up to you to optionnaly plug it to a MQTT broker. I personnally plugged it to Mosquitto and the InfluxDB/Grafana/OpenHAB stack.
Many thanks to Marvin Roger (https://github.com/marvinroger) and his AsyncMqtt library which allows this fridge to run when no connection to my mwtt server is available :)