As I was once looking to buy new thermostats, but failed to find a suitable one, and having been tinkering with ESP chips and soldering, I decided to look inside my current thermostats.
Amazingly, I noticed a slot that looked exactly like it would fit and ESP chip. I think they produce the circuit boards the same, and add the chip to sell at twice the price.
For anyone looking to do the same from search, the exact model of the thermostat is:
hw_version: "V1.2 20200318" model: "HY08-1MB_WE3_V12_TWT / HY08WE1W(24)"
So I flashed ESPHome onto an ESP12, soldered it on, plugged the thermostat back in and was happily greeted with a new available device. Sadly ESPHome didn’t provide a compatible component for thermostats. So i found a project - GitHub - klausahrenberg/WThermostatBeca: Replaces original Tuya firmware on Beca thermostat with ESP8266 wifi module
Which worked! (version 1.19 only, the beta versions didn’t work)
I added it to Home Assistant with some problems, since the firmware mqtt messages have different formats.
mqtt:
climate:
- name: Livingroom
object_id: thermostat_78169
mode_command_topic: "livingroom/thermostat/set/mode"
mode_state_topic: "livingroom/thermostat/state/mode"
modes:
- "auto"
- "off"
- "heat"
- "cool"
current_temperature_topic: "livingroom/thermostat/state/temperature_template"
temperature_command_topic: "livingroom/thermostat/set/targetTemperature"
temperature_state_topic: "livingroom/thermostat/state/targetTemperature"
power_command_topic: "livingroom/thermostat/set/deviceOn"
initial: 23
max_temp: 30
min_temp: 18
precision: 1.0
temp_step: 1
json_attributes_topic: "livingroom/thermostat/state"
json_attributes_template: "{{ value_json | tojson }}"
retain: true
device:
identifiers: "thermostat_78169"
hw_version: "V1.2 20200318"
model: "HY08-1MB_WE3_V12_TWT / HY08WE1W(24)"
manufacturer: "Node Next"
suggested_area: livingroom
sw_version: "1.19"
configuration_url: http://thermostat_78169.local/config
The firmware doesn’t say when it’s heating or off, so I created a an automation to publish the state, depending on current_temperature and target_temperature
- service: mqtt.publish
data:
topic: bedroom/thermostat/state/mode
payload: >-
{% if states('sensor.thermostat_10373_deviceon') == 'True' %}
{% if (states('sensor.thermostat_10373_target') | int + 1) > states('sensor.thermostat_10373_temperature') | int %}
heat
{% elif (states('sensor.thermostat_10373_target') | int + 1) <states('sensor.thermostat_10373_temperature') | int %}
cool
{% else %}
auto
{% endif %}
{% else %}
off
{% endif %}
retain: true
Which now nicely colors the thermostat in Lovelace UI when it’s heating orange, cooling blue, etc.
Now I’m very happy with a homemade smart thermostat.
During the process I blew 1 thermostat up (wrong firmware OTA update made it switch on and off quickly), and blew the main heating fuse. But all good now, the fuse was 50 cents. 
Just got to find a new thermostat for the cold bathroom now…
Hope it helps someone with the same device, it seems a cheap common one in EU. 
