RS485 Interface for Tylö/Helo Sauna Heaters

This interface was specifically developed and tested for the Tylö Sense Pure heater. Other Sauna360 heaters may also work, but compatibility is not guaranteed. This device does not emulate a panel and, therefore, cannot serve as a replacement.

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Hardware

MCU

This project utilizes an ESP32-S3 (ESP32-S3-WROOM-1) paired with an external RS485-to-UART interface based on the MAX485. Although the ESP32-C6 is theoretically capable of handling the task, ESPHome currently lacks support for suitable UART hardware interrupts.

Door Sensor

The door sensor used in this project is an ABUS FU7350W.

External Switch

The external switch with LED feedback used in this project can be found here.

Sauna PCB

Mikrocontroller: PIC32 MX150F128D
Differential Bus Transceivers: TI SN65176B

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Pinout and Wiring Diagram

Wiring Diagram

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Connector Pinout (Western Connector 4P4C)

Pin	Signal
1	A
2	B
3	12V DC
4	GND

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Pinout Table

Pos	Unit	Use pin	Comment	Pin 1	Pin 2	Pin 3	Pin 4
1 - NTC	Temp. sensor in the room	2, 3	10kΩ. May also be connected at Pos 4 - SEC/NTC.	-	10kΩ	10kΩ	-
2 - EXT SWITCH	External switch	3, 4	Start/Stop. Momentary or latching switch	-	-	Switch	Switch
	External switch with LED indication	2, 3, 4	Start/stop operation. 12VDC max. 40mA	-	LED GND	Switch	Switch / LED 12V
3 - DOOR SWITCH	Door contact (NO)	3, 4		-	-	Switch	Switch
	Door contact (NO) with LED indication	2, 3, 4	12VDC max. 40mA.	-	LED GND	Switch	Switch / LED 12V
4 - SEC/NTC	Combined temperature sensor/cut-out in the room	2, 3	Only used for certain products.	Sec	10kΩ	10kΩ	Sec
5-8 - RS485	Control panels	1, 2, 3, 4	Tylö Pure control panel, ESP32 (RS485)	A	B	12V	GND

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Communication

RS485 UART Communication Settings

Baud	Bits	Parity	Stopbit
19200	8	Even	1

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Message Format and Essential Bits

These details have been reverse-engineered by analyzing intercepted communication between a heater and its control panel. As such, the list may not be complete or fully accurate. Further testing and validation may be required to confirm all behaviors and formats.

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Keep-Alive Messages

Start of Frame (SOF)	Address ID	Message Type / Origin	Data	CRC	End of Frame (EOF)
0x98	0x40	0x06	0 Bytes	2 Bytes	0x9C
		0x07
Explanation: 0x06: Sent by the heater as a Keep-Alive request. 0x07: Sent by the control panel as a Keep-Alive acknowledgment.

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Message Structure

Start of Frame (SOF)	Address ID	Message Type / Origin	Code	Data	CRC	End of Frame (EOF)
0x98	0x40	0x06 (Heater Request)	2 Bytes	0–4 Bytes	2 Bytes	0x9C
		0x07 (Panel Command)	2 Bytes
		0x08 (Heater Data)	2 Bytes
		0x09 (Panel Data / ACK?)	2 Bytes

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Essential Codes and Their Descriptions

Code	Description
0x3400	Light and Heater Status
0x4002	Bath Time and Maximum Temperature
0x4003	Overheating PCB Limit
0x6000	Temperature Data: Encodes current and target sauna temperature.
0x7000	Request Heater Status Changes: Panel -> Heater
0x7180	Light and Heater Status: Heater -> Panel
0x9400	Total Uptime
0x9401	Remaining Time: Indicates the remaining time of the current sauna session.
0xB000	Error Codes
0xB600	Sensor Errors

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Timing

Required timing to send 0x07 (Panel Command) to heater.

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ESPHome Default Configuaration

substitutions:
  device_name: "tylo"

external_components:
  - source:
      type: git
      url: https://github.com/f-io/esphome-tylo/
      ref: main
    refresh: 1s
    components: [ sauna360 ]
    
esphome:
  name: ${device_name}
  friendly_name: ${device_name}
  comment: ${device_name} sauna controller
  area: Sauna

esp32:
  board: esp32-s3-devkitc-1

logger:
  level: WARN
  baud_rate: 0

api:
  encryption:
    key: ""

ota:
  - platform: esphome
    password: ""

wifi:
  power_save_mode: NONE
  ssid: !secret wifi_ssid
  password: !secret wifi_password

uart:
    tx_pin: GPIO41
    rx_pin: GPIO42
    baud_rate: 19200
    data_bits: 8
    parity: EVEN
    stop_bits: 1

sauna360:
  id: sauna360_component

binary_sensor:
  - platform: sauna360
    heater_status:
      name: "Heater State"
  - platform: sauna360
    light_status:
      name: "Light State"
  - platform: sauna360
    ready_status: 
      name: "Ready State"

sensor:
  - platform: wifi_signal
    name: "${device_name} WiFi Signal"
    update_interval: 60s
    icon: "mdi:wifi"
  - platform: sauna360
    id: current_temperature_sensor
    current_temperature:
      name: "Current Temperature"
  - platform: sauna360
    setting_temperature:
      name: "Setting Temperature"
  - platform: sauna360
    remaining_time:
      name: "Remaining Time"
  - platform: sauna360
    setting_bath_time:
      name: "Setting Bath Time"
  - platform: sauna360
    total_uptime:
      name: "Total Uptime"
  - platform: sauna360
    max_bath_temperature:
      name: "Max Bath Temperature"
  - platform: sauna360
    overheating_pcb_limit:
      name: "Overheating PCB Limit"

number:
  - platform: sauna360
    bath_temperature:
      name: "Bath Temperature"
      id: bath_temperature
      mode: box
      bath_temperature_default: 90 # default value
  - platform: sauna360
    bath_time:
      name: "Bath Time"
      mode: box
      bath_time_default: 300 # default value
  - platform: sauna360
    max_bath_temperature:
      name: "Max Bath Temperature"
      mode: box
      max_bath_temperature_default: 110 # default value

switch:
  - platform: sauna360
    light_relay:
      name: "Light"
  - platform: sauna360
    heater_relay:
      name: "Heater"
      id: heater_relay_switch

text_sensor:
  - platform: sauna360
    heater_state:
      name: "Heating Element"

time:
  - platform: homeassistant

climate:
  - platform: sauna360
    id: sauna_climate
    name: "Sauna Climate"
    sauna360_id: sauna360_component
    bath_temperature_number_id: bath_temperature
    heater_relay_id: heater_relay_switch
    visual:
        min_temperature: 40
        max_temperature: 110
        temperature_step: 1.0

Integration Example

Home Assistant

Apple Homekit