README.md

Honeywell Resideo R200C2-A Mod

Connect your Resideo CO2 monitor to Home Automation via MQTT This code is running on an ESP8266 module ESP-12F

• Reading CO2 ppm via RX
• Reading Humidity and temperature by sniffing the I2C

Dependencies

Uses the Home Assistant MQTT Library

• https://github.com/dawidchyrzynski/arduino-home-assistant

Some helpers

• https://github.com/Pluimvee/Pluimvee-ArduinoLib/blob/master/src/DatedVersion.h
• https://github.com/Pluimvee/Pluimvee-ArduinoLib/blob/master/src/Logging.h

Hardware

• 4x Honeywell voor €84 (inc. shipment) https://www.ibood.com/nl/s-nl/o/2x-honeywell-resideo-co2-monitor-detector/987304
• 4x ESP-12F voor €6 (inc. shipment) https://nl.aliexpress.com/item/4001157391459.html

€23 per unit

Wiring

The wiring of the ESP8266 ESP12F module to the Honeywell Resideo

Research

Sniffing the communication of the CHT8305 Humidity/Temperature sensor I used the below code. This code is using interrupts for more stability

https://github.com/Pluimvee/I2C-sniffer/blob/main/I2C-sniffer.ino

The SDA/SCL pins can also be found on the display-board-connector, and on the backside of the display-board. I tried to solder some pins on the backside of the display-board however the test-pads are to week to hold any pins. Therefore I soldered some pins into the pads next to the battery connector.

Sniffing the communication of the CM1106 sensor I used a TTL-2-USB bridge https://nl.aliexpress.com/item/1005002007754292.html

Using this module I found out that the pins TX and RX on the CM1106 module have the same data streams as found on the D and C pins behind the display module.

• The C has the same data as found on the RX pin of the CO2 module -> 11 01 01 ED. Therefore I think C stands for Command and the instruction send by the controller to the CO2 module is found there.
• The D has the same data as found on the TX pin of the CO2 module -> 16 05 01 DF1-DF4 CS. I asume D stands for Data and there we can find the response of the CO2 module send to the controller.

Therefore we only need to connect the D(ata) pin to the RX of your ESP, and do not need to solder anything on the CM1106 module itself.

My graditude to the research and work of the following tweakers:

• Bartvb (https://gathering.tweakers.net/forum/list_message/78228570#78228570)
• Soepstengel (https://gathering.tweakers.net/forum/list_message/77882454#77882454)
• Skix_Aces (https://gathering.tweakers.net/forum/list_message/78427188#78427188)
• ThinkPad (https://gathering.tweakers.net/forum/list_message/77642990#77642990)