Tech SBUS to MQTT gateway
The script listens to communication between "Tech Sterowniki" devices over a RS485 bus (Tech SBUS protocol) and publishes the messages over MQTT.
It allows to send temperature change commands.
It also publishes MQTT discovery messages for Home Assistant so if the MQTT integration is enabled all zones will automatically become visible in Home Assistant.
It works fully locally, no connection to the Tech cloud / eModul is used. The updates are published over MQTT immediately once received from the device.
It requires an RS485 interface, I use USB to RS485 adapters that contain UART chip CH340C and RS485 transceiver MAX485, cost around $2-$3 and seem to be very reliable (I had one with FT232RL and it sometimes hung but maybe I had a broken one?).
The script requires a configuration file. It has to be placed in the script's directory, have name tech-sbus-mqtt.conf and the following yaml structure:
controllers:
- name: Upstairs
address: 00-00-00-01
serial: 00001
model: L-X WiFi
regulators:
- name: Bathroom
address: 00-00-00-02
serial: 0001
model: R-12S
default_duration: 1441
- name: Childrens bedroom
address: 00-00-00-03
serial: 0002
model: R-12S
default_duration: 1441
- name: Master bedroom
address: 00-00-00-04
serial: 0003
model: R-12S
default_duration: 1441
- name: Downstairs
address: 00-00-00-05
serial: 00002
model: L-X WiFi
regulators:
- name: Living room
address: 00-00-00-06
serial: 0004
model: R-12S
default_duration: 1441
- name: Kitchen
address: 00-00-00-07
serial: 0005
model: R-12S
default_duration: 1441
- name: Bathroom downstairs
address: 00-00-00-08
serial: 0006
model: R-12S
default_duration: 1441
serial_ports:
- /dev/ttyUSB0
- /dev/ttyUSB1
log_file: tech-sbus-mqtt.log
log_level: INFO
pid_file: /tmp/tech-sbus-mqtt.pid
mqtt:
hostname: 192.168.1.15
port: 1883
topic_prefix: techcontrollers
# username: tech
# password:
# tls: yes
# tls_verify_peer: yes
# tls_ca_cert:
# tls_client_cert:
# tls_client_key:
The example above contains a configuration for two central controllers (one for each floor) and 3 room regulators connected to each of them. Each controller is on a separate RS485 bus. Devices' serial numbers should be printed on stickers on their back but serial numbers and model names aren't required for the script to function properly. The devices' addresses are crucial. In order to get the addresses of the room regulators and controllers I recommend to start the script with the following basic configuration:
serial_ports:
- /dev/ttyUSB0
log_file: tech-sbus-mqtt.log
log_level: DEBUG
pid_file: /tmp/tech-sbus-mqtt.pid
mqtt:
hostname: 192.168.1.15
port: 1883
topic_prefix: techcontrollers
It'll listen on one serial port and will print all received messages to MQTT and the log_file (DEBUG mode). Once it's listening, restart the Tech controller. During boot it sends the date&time message, search for the following in the log:
$ grep -a timestamp tech-sbus-mqtt.log
2025-04-10 20:53:36 INFO aa-bb-cc-dd->ff-ff-ff-ff,timestamp,1744318421,-5
aa-bb-cc-dd is the address of your controller.
Then search for the following patterns (where aa-bb-cc-dd is your controller's address):
$ grep -a '\->aa-bb-cc-dd' tech-sbus-mqtt.log
Messages similar to the below will show up:
2025-04-10 21:49:04 DEBUG a2-25-d9-fc->aa-bb-cc-dd,room temperature,21.6
2025-04-10 21:49:04 DEBUG a2-25-d9-fc->aa-bb-cc-dd,humidity,49.2
2025-04-10 21:49:05 DEBUG e2-a5-80-54->aa-bb-cc-dd,humidity,53.7
2025-04-10 21:49:14 DEBUG a2-25-d9-fc->aa-bb-cc-dd,room temperature,21.6
2025-04-10 21:49:14 DEBUG a2-25-d9-fc->aa-bb-cc-dd,humidity,49.1
2025-04-10 21:49:20 DEBUG e2-a5-80-54->aa-bb-cc-dd,room temperature,21.2
The addresses before the "->" are addresses of your room regulators. If there're many of them, you can figure out the room/zone for each address by checking and comparing the humidity and temperatures on their displays. You can also temporarily change the target temperature in a zone to see a message as follows:
2025-04-10 21:57:19 DEBUG 64-e5-70-3d->aa-bb-cc-dd,target temperature (2),20.5
2025-04-10 21:57:19 DEBUG 64-e5-70-3d->aa-bb-cc-dd,target temperature time (2),60
2025-04-10 21:57:19 DEBUG Publishing msg: 60 topic: techcontrollers/64-e5-70-3d/temperature/air/target2/duration
2025-04-10 21:57:19 DEBUG Publishing msg: 20.5 topic: techcontrollers/64-e5-70-3d/temperature/air/target2
2025-04-10 21:57:20 DEBUG aa-bb-cc-dd->64-e5-70-3d,target temperature time,59
2025-04-10 21:57:20 DEBUG Publishing msg: 59 topic: techcontrollers/64-e5-70-3d/temperature/air/target/duration
2025-04-10 21:57:20 DEBUG aa-bb-cc-dd->64-e5-70-3d,target temperature,20.5
2025-04-10 21:57:20 DEBUG Publishing msg: 20.5 topic: techcontrollers/64-e5-70-3d/temperature/air/target
In this example 64-e5-70-3d is the address of the room regulator on which the temperature change was requested and aa-bb-cc-dd is the controller's address.
When you have all the addresses collected, create the full configuration file and restart the script.
Once the script is started and new devices and entities appear in Home Assistant, I recommend to restart the Tech controller(s) so that Home Assistant becomes immediately aware of all the zones and parameters which aren't repeated regularly (for example the target temperatures for each zone).
You can use MQTT to change temperatures.
Temperature change request topic is "topic_prefix/regulator_address/temperature/air/target/set"
The payload is a JSON object with two keys:
temperature- decimal number, range 5-35, Celsius degreesduration(optional) - integer, range 0-1441, minutes, values 0 and 1441 have special meanings:0- switches back to the schedule (valid temperature has to be provided in the request although it's not used)1441- sets the target temperature for an indefinite period
If the duration is not provided in the MQTT message, value default_duration from the config file is used - defaults to 1441 (indefinite).
Example MQTT message to set target temperature to 25 degrees for 3 hours on regulator xx-yy-zz-xx:
| topic | message |
|---|---|
| techcontrollers/xx-yy-zz-xx/temperature/air/target/set | {"temperature": 25.0, "duration": 180} |
Example MQTT message to set target temperature to 25 degrees on regulator xx-yy-zz-xx for an indefinite period of time:
| topic | message |
|---|---|
| techcontrollers/xx-yy-zz-xx/temperature/air/target/set | {"temperature": 25.0, "duration": 1441} |
Example MQTT message to switch back to the schedule on xx-yy-zz-xx:
| topic | message |
|---|---|
| techcontrollers/xx-yy-zz-xx/temperature/air/target/set | {"temperature": 25.0, "duration": 0} |
Standard Home Assistant climate cards don't support setting duration, only the temperature. Automations can be used to achieve that.
The script is a result of my reverse engineering of the protocol so only limited functionality is available at the moment. If time permits new features may be added in future because some more data is transmitted. Everyone's encouraged to contribute.
What I currently know about the protocol: TECH_RS485_PROTOCOL
- L-X WiFi - central controller
- R-12S - wired room regulator with air temperature sensor, humidity sensor and a connector for floor temperature NTC sensor
- CH340/CH341 RS485<->USB converter
- Waveshare RS485 CAN HAT for Raspberry Pi
- Dockerfile, docker-compose