esphome-daikin-s21

ESPHome component to control Daikin indoor mini-split units using the wired protocol available over S21 and related ports.

A big thanks to:

• revk for work on the fantastic Faikout (née Faikin) project, which was the primary inspiration and guide for building this ESPHome component. In addition, the very active and resourceful community that project has fostered that has decoded much of the protocol.
• joshbenner, the original author of this integration. His repository would be my preferred place to commit patches to avoid fragmentation, but he lacks the time at the moment to manage the project.
• The users of this project who have contributed, tested or offered feedback.

Features

Climate

• Setpoint temperature.
• Selectable climate modes OFF, HEAT_COOL, COOL, HEAT, FAN_ONLY and DRY.
• Climate action reporting. See what your unit is trying to do, e.g. heating or cooling while in HEAT_COOL.
• Fan modes auto, silent and 1-5.
• Swing modes horizontal, vertical, and both.
• Untested support for Powerful and Econo presets ("Boost" and "Eco"). My unit doesn't support these over the wired protocol.
• Optional humidity reporting.
• Limits for commanded setpoints. Defaults should work fine, but if your unit is different they can be overridden.

The standard Daikin control loop has a few deficiencies:

• The setpoint value has 1.0°C granularity.
• The current temperature feedback value has 0.5°C granularity.
• The current temperature sensor is located in the unit, in most cases a wall unit placed higher in a room. This reading doesn't always reflect the temperature felt by occupants.

Because of these, the climate component implements a separate loop on top of the Daikin internal one. An external temperature sensor can be used to provide a more accurate and precise reference and an offset applied to the internal Daikin setpoint. The internal temperature sensor can also be used for this functionality to drive the coarse setpoint around the more granular temperature sensor. The rate at which this secondary loop runs must be configured with the update interval when using this mode. All of this is downstream of Daikin's reported temperature precision and relatively broad control loop hysteresis, so it's far from ideal but can compensate for a difference in temperature between the unit and your space.

Sensor

Sensors in ESPHome are geared more towards an ADC value that can be filtered as necessary. The values read from the Daikin unit are pre-processed and won't normally require averaging filters and the like. The sensor component supports a configurable update interval that will publish the current values periodically. To make this reporting more responsive, the user can set this value to zero and every update from the unit, interesting or not, will be published. To reduce spam, please configure a delta filter on your sensors and only changes will be published over the network. See the example configuration.

• Inside temperature (usually measured at indoor air handler return)
• Outside temperature (outside exchanger)
• Coil temperature (indoor air handler's coil)
• Target temperature (internal setpoint, modified by special modes)
• Fan speed
• Vertical swing angle (directional flap)
• Compressor frequency (outside exchanger)
• Humidity (not supported on all units, can report a consistent 50% if not present)
• Unit's demand from outside exchanger

v2 protocol units may also support:

• IR counter that increments when the remote is used (untested)
• Total power consumption in kWh (untested)
• Outdoor unit capacity in indoor units

Binary Sensor

New, extracted from the unit and system state bitfields. Still need to observe to see how valuable these are. I may remove the redundant ones in the future. Not all units support these.

• Powerful
• Defrost
• Active (Actively controlling climate, climate action can tell us this)
• Online (In a climate controlling mode, climate mode can tell us this)
• Refrigerant Valve (shadows active?)
• Short Cycle Lock (3 minute compressor lockout)
• System Defrost (shadows defrost?)
• Multizone settings conflict

Text Sensor

There's not a lot of string data available in protocol v0 units. v2 protocol units may support, though untested:

• Software Version

If you've read the Faikout wiki you'll see many more queries available than what this project supports. I've added a text_sensor component to read these raw values out for debugging and protocol decoding use, without having to add a dedicated sensor. Normally you wouldn't need to use this, but if a value looks interesting you can see the value change over time in Home Assistant. I'd prefer if we use this just to confirm a query works and then add proper support, rather than trying to interpret the string. Open an issue with details if you want a sensor added.

Limitations

NOTE: Currently there's a serious issue when using the Arduino framework. If flashed OTA you may lose communication and require a physical reflashing (annoying if your board in inside your air handler). Please stick to the ESP-IDF PlatformIO framework for now (Arduino is an extra shim over the ESP-IDF SDK anyways). See the framework selection in the configuration example. As of this writing, independent UART pin inversion control also wasn't possible.

• This code has only been tested on ESP32 pico and ESP32-S3. It compiles for ESP8266.
• Tested with 4MXL36TVJU outdoor unit and CTXS07LVJU, FTXS12LVJU, FTXS15LVJU indoor units.
• Powerful and econo modes are untested (no v2 hardware).
• Does not support comfort or presence detection features on some models.
• Does not interact with the indoor units schedules (do that with HA instead).
• Higher protocol versions have limited support due to the equipment available to me, though I'm happy to try to work with you.
• Daikin's internal R&D departments must be a bit chaotic. The latest models might have inferior command sets to those released years ago.

Hardware

Please see the Faikout wiring page for detailed documentation including pinouts, alternate connectors with images. The below is just a quick reference overview.

NOTE: The Daikin connector's Vcc provides >5V, so if you intend to power your board with this pin, be sure to test its output and regulate voltage accordingly. Mine supplies 14.5V.

For communications pins, I found mine pulled up internally to 5V by the Daikin board. I've read some users don't see this, so verify with a multimeter. You may need to add your own external pullups or make use of a level shifting circuit. Cheap level shifter modules are available that can make use of the provided 5V reference to do this if you'd prefer. If you are powering your device externally you should still connect a ground reference for the communications.

S21 Port

On my Daikin units, the S21 port has the following pins:

1. Vref (5V) Reference for communications, not to be used for powering your device. Sometimes N/C.
2. TX (5V) Daikin Tx, ESPHome Rx
3. RX (5V) Daikin Rx, ESPHome Tx
4. Vcc (>5V!)
5. GND

The S21 plug is JST EHR-5 and related header B5B-EH-A(LF)(SN), though the plug pins are at standard 2.5mm pin header widths. I was able to locate headers and precrimped wire leads on Aliexpress for a low cost.

S403 Port

The project has been reported to work on a unit with the S403 connecter as This has the same communication interface with a little additional functionality, and most importantly to note, mains voltage exposed on a pin. Do not connect anything to pin 10. Don't populate it in your plug.

1. Vcc (>5V!)
2. JEM-A OUT (pull down = ON)
3. JEM-A IN (pull down = toggle switch)
4. TX (5V) Daikin Tx, ESPHome Rx
5. RX (5V) Daikin Rx, ESPHome Tx
6. GND
7. GND
8. N/C
9. N/C
10. ~327 VDC (Dangerous!)

Housing: JST XAP-10V-1 Contacts: JST SXA-001T-P0.6

PCB Option 1

joshbenner uses the board designed by revk available here. Note that revk's design includes a FET that inverts the logic levels on the ESP's RX pin, and on newer revisions the TX pin as well. When interfacing through a FET the RX line should be configured with a pullup. This handling should be supported with the ESP-IDF framework and regular ESPHome invert pin schema, see the example configuration.

PCB Option 2

I am using ESP32-S3 mini dev boards and directly wiring communication to the S21 port. My Daikin unit pulls our TX line up to 5V, so I've configured my pin as open drain to work with it. The RX line relies on the ESP32's 5V tolerant GPIO pins. For power I am using a cheap 5V -> 3.3V switching module wired into Vcc on the dev board.

Contributing

If you can write C++, great. Even if you're more of a YAML writer and user, your assistance with this project would be helpful. Here are some possible ways:

• Report your experince with different Daikin units. Turning on protocol debugging and getting the protocol and model detection output values would be the first step if you encounter issues and help me learn more about the output of different models.
• Let me know how useful the binary sensor values are and which just shadow other sensor values.

Please consider documenting characteristics of your unit in the appropriate place in the Faikout wiki. I don't want to make an inferior copy of this information if possible. Please don't report issues with this component to them as we don't share a codebase. Some of the readout values here are not byteswapped if we don't otherwise use them so unknown static fields may appear reversed compared to that project. Please verify this when contributing.

See existing issues, open a new one or post in the discussions section with your findings. Thanks.

Configuration

On multihead systems some values that come from the outdoor unit will be the same (accounting for sampling jitter). It's recommended to use ESPHome's subdevice feature to only configure these sensors on your "primary" ESPHome instance as a subdevice to keep individual indoor unit representations cleaner. See the configuration example below. This feature seems designed for the one-to-many case, whereas this system is more of a many-to-one configuration. Locally I have two configuration template files, one for indoor only units and one for a single indoor unit with an outdoor unit subdevice. If I can find a better solution I'll update the example.

When using an external temperature sensor as a room reference instead of the internal Daikin value (which may be misleading due to placement of the unit) it's recommended to change the target_temperature step to 0.5°C to reflect the granularity of the alternate control loop provided. The default is 1.0°C to match Daikin's internal granularity.

esphome:
  min_version: "2025.11"
  devices:
    - id: daikin_outdoor
      name: "Daikin Compressor"

esp32:
  framework:
   type: esp-idf

logger:
  baud_rate: 0  # Disable UART logger if using UART0 (pins 1,3)

preferences:
  flash_write_interval: 72h

external_components:
  - source: github://asund/esphome-daikin-s21@main
    components: [ daikin_s21 ]

uart:
  - id: s21_uart
    tx_pin: GPIO1
    rx_pin: GPIO3
    baud_rate: 2400
    data_bits: 8
    parity: EVEN
    stop_bits: 2

# The parent UART communication hub platform.
daikin_s21:
  uart: s21_uart
  # debug_protocol: true  # please enable when reporting logs!
  # update_interval: 5s  # also supports periodic polling instead of more responsive free run

climate:
  - name: My Daikin
    platform: daikin_s21
    # Settings from ESPHome Climate component:
    # Visual limits and steps can be adjusted to match the granularity of your external sensor:
    # visual:
    #   temperature_step:
    #     target_temperature: 1
    #     current_temperature: 0.5
    # Settings from DaikinS21Climate:
    # supported_modes:  # optional, restricts available modes. off is always supported.
    #   - heat_cool
    #   - cool
    #   - heat
    #   - dry
    #   - fan_only
    # supported_presets:  # optional, enables presets. none is always supported.
    #   - eco
    #   - boost
    # supported_swing_modes:  # optional, restricts available swing modes. off is always supported.
    #   - horizontal
    #   - vertical
    #   - both
    # Optional sensors to use for temperature and humidity references
    # sensor: room_temp  # External, see homeassistant sensor below
    humidity_sensor: daikin_humidity  # Internal, see humidity sensor below
    # humidity_sensor: room_humidity  # External, see homeassistant sensor below
    # or leave unconfigured if unsupported to omit reporting
    # update_interval: 60s # Interval used to adjust the unit's setpoint using reference sensor
    # Daikin internal supported temperature range setpoints, used to prevent sending out of range values to the unit.
    # Defaults should be fine unless your unit differs (see your manual):
    # max_cool_temperature: 32 # maximum setpoint when cool
    # min_cool_temperature: 18  # minimum setpoint when cool or heat_cool
    # max_heat_temperature: 30  # maximum setpoint when heat or heat_cool
    # min_heat_temperature: 10 # minimum setpoint when heat

# Optional additional sensors.
sensor:
  - platform: daikin_s21
    update_interval: 0s
    inside_temperature:
      name: Inside Temperature
      filters:
        - delta: 0.0
    outside_temperature:
      name: Outside Temperature
      device_id: daikin_outdoor
      filters:
        - delta: 0.0
    coil_temperature:
      name: Coil Temperature
      filters:
        - delta: 0.0
    fan_speed:
      name: Fan Speed
      filters:
        - delta: 0.0
    swing_vertical_angle:
      name: Swing Vertical Angle
      filters:
        - delta: 0.0
    compressor_frequency:
      name: Compressor Frequency
      device_id: daikin_outdoor
      filters:
        - delta: 0.0
    humidity:
      id: daikin_humidity
      name: Humidity
      filters:
        - delta: 0.0
    demand:
      name: Demand  # 0-15 demand units, use filter to map to %
      filters:
        - multiply: !lambda return 100.0F / 15.0F;
        - delta: 0.0
    # Protocol Version 2:
    ir_counter:
      name: IR Counter
      filters:
        - delta: 0.0
    power_consumption:
      name: Power Consumption
      filters:
        - delta: 0.0
    outdoor_capacity:
      name: Outdoor Capacity
      device_id: daikin_outdoor
      filters:
        - delta: 0.0
  # optional external reference sensors
  - platform: homeassistant
    id: room_temp
    entity_id: sensor.office_temperature
    unit_of_measurement: °F
    accuracy_decimals: 1
  - platform: homeassistant
    id: room_humidity
    entity_id: sensor.office_humidity
    unit_of_measurement: "%"
    accuracy_decimals: 1

binary_sensor:
  - platform: daikin_s21
    powerful:
      name: Powerful
    defrost:
      name: Defrost
    online:
      name: Online
    valve:
      name: Valve
    short_cycle:
      name: Short Cycle
      device_id: daikin_outdoor
    system_defrost:
      name: System Defrost
      device_id: daikin_outdoor
    multizone_conflict:
      name: Multizone Conflict
      device_id: daikin_outdoor

# raw case-sensitive query monitoring for debugging
text_sensor:
  - platform: daikin_s21
    software_version:
      name: Software Version
#     queries:
#       - RK

Here is an example of how daikin_s21 can be used with inverted UART pins and an RX pullup (newer Faikout PCB rev):

uart:
  - id: s21_uart
    tx_pin:
      number: GPIO48
      inverted: true
    rx_pin:
      number: GPIO34
      inverted: true
      mode:
        input: true
        pullup: true
    baud_rate: 2400
    data_bits: 8
    parity: EVEN
    stop_bits: 2

daikin_s21:
  uart: s21_uart

Here's an example of ESP32 dev board using direct wiring:

uart:
  - id: s21_uart
    tx_pin:
      number: GPIO43
      mode:
        output: true
        open_drain: true  # daikin pulls up to 5V internally
    rx_pin: GPIO44
    baud_rate: 2400
    data_bits: 8
    parity: EVEN
    stop_bits: 2

daikin_s21:
  uart: s21_uart