(see our video for the assembly process, but please note that before ESP32 we tried to make it all on NodeMCU+ESP hybrid board that we had already).

For online functionality, you have to obtain an API key from SaveEcoBot. The request form, documentation, and terms of use are available here: https://www.saveecobot.com/en/static/api
For optimization, the IDs of the control points are hardcoded as they never change.

Choose a display produced later than around 1995 (those almost always have 3 circuit boards instead of 5). Check if there are K50-6 electrolytic capacitors; if any are present, it’s a good idea to replace them as a precaution. On the upper board, find the chip К155АГ3, which is a dual monostable multivibrator. Cut the connection coming to К155АГ3 pin 1 and wire the connector’s pin 20A (address signal A8) directly to pin 1 of К155АГ3.

Replace the four screws securing the display’s enclosure with four spacer standoffs.

Prepare the PSU and ensure the voltage is 12V. Attach the DC-DC converters. We used one converter for the display and another for the ESP32. How you assemble the power system depends on your setup, but in the end, the PSU should provide:    a) a separate 12V + GND power line for the MS6205 matrix    b) a separate 5V + GND line for MS6205 logic    c) a power cable for the ESP32. If no expansion board is used, it is USB-C. If an expansion board is used, it can be either Micro-USB or a 12V line, as most boards accept anything between 6–16V (refer to the markings on the board).

IMPORTANT: According to its datasheet, NEVER exceed 12.6V on the power line going to the MS6205 — it will burn out.

Optionally, you can power the CAJOE RadiationD module directly using its power connector; however, it can also be powered from the ESP32’s power lines via P3 connector.

Daisy-chain the I²C sensors — the real-time clock, AHT10, and BMP180. It’s a good idea to make the wires to the temperature sensor long enough to place it at the bottom of the device. I, however, was more interested in internal readings, so I placed it on a shared chassis.

Position and secure the ESP32 board, the sensors from step #4, and the CAJOE RadiationD module on a plastic chassis using spacer standoffs. It’s recommended to carefully shield the native glass detector of the RadiationD, or replace it with a matching SBM-20 detector. Always remember that there are HUNDREDS of volts on the detector during operation. Use the protective cover that normally comes with the module or make your own.

a) Connect the shared SCL and SDA lines from the sensors (step #4) to GPIO 22 and GPIO 21 of the ESP32, respectively. Connect their 5V and GND lines to the power headers of the expansion board.    
b) The signal pin on the P3 connector of the CAJOE RadiationD is incorrectly labeled as VIN. Connect it to the selected GPIO on your controller (in our case, GPIO 34 on the ESP32).

Place and secure the chassis onto the spacer standoffs at the back of the MS6205.

You can make a cable or a PCB. We used a cut-off piece of a Soviet prototype PCB that had a slot for a СНП connector, as it takes up less space. Connect the cable to the ESP32 GPIOs according to the cable wiring schematic. This gives you a self-contained display + logic block. Note that there’s also a version for Arduino Uno, which can be handy for quick testing of display functionality – test code find in files.

Program the ESP32 using `esp_dosimeter.ino`. Don’t forget to specify your Wi-Fi SSID, password, and SaveEcoBot API key.