ESP based WiFi controller for itho central ventilation boxes

(note: I'm in no way a professional hardware/software engineer and have no background in these subjects. I like this for a hobby, to learn and to share my projects)

Control the Itho Daalderop Eco Fan RFT using basically only an ESP32 directly communicating with the Itho by i2c protocol.

The code will give you full remote control over the Itho Eco Fan RFT with one simple add-on module and without further changes to the Itho box.

Two versions of the firmware have been included:

• A simple version with hardcoded SSID and password.
• A more advanced version that starts an access point when no SSID can be connected and allows you to setup the device specifics (Wifi and MQTT settings) and save them on SPIFFS using the webinterface.

The firmware for the Attiny, which handles the i2c initialisation is the same for both the simple and advanced Wemos firmware.

An important note about the firmware:

• The add-on is able to control the itho box in standard or medium mode setting only. This means you can use the original remote but if you leave the itho box in low or high setting the itho won't accept commands from the add-on. This is itho designed behaviour.

I2C protocol:

The Itho fan and add on modules both communicate as I2C master.

First the main pcb sends a start message:

Address (0x41),Write
Data: (0xC0),(0x00),(0x00),(0x00),(0xBE)

The add-on then replies (as slave):

Address (0x41),Write
Data: (0xEF),(0xC0),(0x00),(0x01),(0x06),(0x00),(0x00),(0x09),(0x00),(0x09),(0x00),(0xB6)

After which the main pcb confirms with another message:

Address (0x41),Write
Data: (0xC0),(0x00),(0x02),(0x05),(0x00),(0x00),(0x09),(0x60),(0x00),(0x4E)

After these initial init messages back and forth the add-on needs to switch to i2c master and sends speed commands to the main pcb like follows:

Address: (0x00),Write
Data: (0x60),(0xC0),(0x20),(0x01),(0x02),(b),(e),(h)

Where:
uint8_t b = target speed (0 - 254)
uint8_t e = 0
uint8_t h = 0 - (67 + b)

It is possible to have other values for e (0, 64, 128, 192) for even more control steps, the complete formula for h will be:

uint8_t h = (0-e) - (67+b)

Hardware:

A sample hardware design (KiCad) is included, this module can be plugged on the Itho main PCB directly without extra components.
*Tested with Itho Daalderop CVE from late 2013 and 2019 (PCB no. 545-5103 and 05-00492)

PoC is done and working, PCBs have been ordered. I will update this page when the boards arrive and are proven to be working.
PCB done and and tested to be working fine!
I have a few assembled boards left for those who want to try this as well, you can find them on my Tindie store:
https://www.tindie.com/products/19680/

BOM:

Change of components version 2.x: Changed the wemos to the much faster ESP32 with more memory etc. Also easier to produce mechanically. Other change of components are to accomodate this change. This version also added the option to solder a CC1101 RF module to be able to receive itho RF signals

Change of components version 1.2: The Wemos boots too slow too often to receive the first I2C message from the Itho box. An Attiny 1614 was added to handle the init. After power-on the Attiny starts executing user code after about 65ms instead of +/-130ms of the Wemos. 130ms is about the point where the itho Box sends its first message.

Change of components version 1.1: The ISO1540/ADUM 1250 ARZ solution did not work as expected. That's why for version 1.1 I switched to a quite common BSS138 MOSFET based logic level converter solution and replaced the other components with SMDs too. The SMD components are all 1206 in size so quite easy to solder by hand.

Choice of components version 1.0:

ESP8266 NodeMCU DevKit (https://github.com/nodemcu/nodemcu-devkit-v1.0) or WeMos D1 mini (https://docs.wemos.cc/en/latest/d1/d1_mini.html): readily available at low prices. Easy to integrate in projects.

ISO1540/ADUM 1250 ARZ: not the cheapest logic level convertor option but special designed for i2c and a one chip solution, SMD but still quite easy to solder by hand.

Recom R-78E5.0-1.0: the regulator (7805) on the itho mainboard is not suitable to drive extra loads like a esp8266/esp32. Luckily there is a pin on the mainboard that holds the output from the main power supply (about 16,3 volts and definitely able to handle more than the 500mA of the on board regulator). Placing a 7805 (or similar) on the add-on board is possible but will probably generate lots of heat (up to 5 watts) because of big voltage drop. That's why I selected the DC-DC converter from recom, very small package, high efficiency (90%).

Credits for the basic firmware:
Web interface based on: https://github.com/SasaKaranovic/ESP-IoT-Dimmer
MQTT implementation based on: https://github.com/srijansaxena11/ESP8266-MQTT-WiFi-Dimmer-PIR/