Native remote_temperature_source weird rounding.

[markfen88]

It's hard to explain this as there are many caveats but I will try anyways.

The "Current Temp" being sent/received is not accurate. I have a remote temperature source that is in C so I do not need the Fahrenheit compatibility mode but I find that using Fahrenheit compatability mode will give me more granular control as when I have it in C it is only "rounding" (does weird math were 23.3-24.2 is 24C) to the nearest whole number and not allowing any decimal changes.

Here is a screenshot

Also for some reason I can not get Target temp to do more fine tuning past .5 increments. I have tried everything and its not working.

Here is my config

substitutions:
  name: heatpump-1
  friendly_name: GreatRoom
  remote_temp_sensor: sensor.livingthermostat_temp # Homeassistant sensor providing remote temperature

esphome:
  name: mitsubishicontroller
  friendly_name: MitsubishiController

esp32:
  board: esp32dev
  framework:
    type: esp-idf

# Enable logging
logger:
  #  hardware_uart: UART1 # Uncomment on ESP8266 devices
  level: INFO
  logs:
    EVT_SETS: INFO
    WIFI: INFO
    MQTT: INFO
    WRITE_SETTINGS: INFO
    SETTINGS: INFO
    STATUS: INFO
    CN105Climate: WARN
    CN105: INFO
    climate: WARN
    sensor: WARN
    chkSum: INFO
    WRITE: WARN
    READ: WARN
    Header: INFO
    Decoder: INFO
    CONTROL_WANTED_SETTINGS: INFO
#  level: DEBUG
#  logs:
#    EVT_SETS : DEBUG
#    WIFI : INFO
#    MQTT : INFO
#    WRITE_SETTINGS : DEBUG
#    SETTINGS : DEBUG
#    STATUS : INFO
#    CN105Climate: WARN
#    CN105: DEBUG
#    climate: WARN
#    sensor: WARN
#    chkSum : INFO
#    WRITE : WARN
#    READ : WARN
#    Header: INFO
#    Decoder : DEBUG
#    CONTROL_WANTED_SETTINGS: DEBUG

# Enable Home Assistant API
api:
  encryption:
    key: "<NOTREAL>"

ota:
  - platform: esphome
    password: "<NOTREAL>"

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Mitsubishicontroller"
    password: "<NOTREAL>"

#ethernet:
#  type: LAN8720
#  mdc_pin: GPIO23
#  mdio_pin: GPIO18
#  clk:
#    pin: GPIO0
#    mode: CLK_EXT_IN
#  phy_addr: 1
#  power_pin: GPIO16

captive_portal:

uart:
  id: HP_UART
  tx_pin: GPIO14
  rx_pin: GPIO15
  baud_rate: 2400

external_components:
  - source: github://echavet/MitsubishiCN105ESPHome
#    refresh: 0s

sensor:
  # Uptime sensor.
  - platform: uptime
    name: Uptime

  # WiFi Signal sensor.
  - platform: wifi_signal
    name: WiFi Signal
    update_interval: 120s

  - platform: homeassistant
    id: ha_remote_temp
    name: "Remote Temperature Sensor"
    entity_id: ${remote_temp_sensor} # Replace with your HomeAssistant remote sensor entity id, or include in substitutions
    internal: false

# Enable Web server.
web_server:
  port: 80

# Sync time with Home Assistant.
time:
  - platform: homeassistant
    id: homeassistant_time

# Text sensors with general information.
text_sensor:
  # Expose ESPHome version as sensor.
  - platform: version
    name: ESPHome Version
  # Expose WiFi information as sensors.
  - platform: wifi_info
    ip_address:
      name: IP
    ssid:
      name: SSID
    bssid:
      name: BSSID

# Create a button to restart the unit from HomeAssistant. Rarely needed, but can be handy.
button:
  - platform: restart
    name: "Restart ${friendly_name}"

# Creates the sensor used to receive the remote temperature from Home Assistant
# Uses sensor selected in substitutions area at top of config
# Customize the filters to your application:
#   Uncomment the first line to convert F to C when remote temps are sent
#   If you have a fast or noisy sensor, consider some of the other filter
#   options such as throttle_average.
climate:
  - platform: cn105
    id: hp
    name: "${friendly_name}"
    icon: mdi:heat-pump
    visual:
      min_temperature: 10 # Adjust to your unit's min temp. SmartSet units can go to 10C for heating
      max_temperature: 31
      temperature_step:
        target_temperature: 0.1
        current_temperature: 0.1
    remote_temperature_source:
      sensor_id: ha_remote_temp       # References the sensor declared above
      info:                           # Optional: exposes a text sensor showing the source name
        name: "Remote Temp Source"
    #remote_temperature_timeout: 30min
    #remote_temperature_keepalive_interval: 20s
    # Fahrenheit compatibility mode - uses Mitsubishi's "custom" unit conversions, set to
    # "standard" (or "alt") for better support of Fahrenheit units in HomeAssistant.
    # Options: "disabled" (default), "standard", "alt"
    #fahrenheit_compatibility: "disabled"
    update_interval: 2s
    debounce_delay: 100ms
    # Various optional sensors, not all sensors are supported by all heatpumps
    outside_air_temperature_sensor:
      name: Outside Air Temp
      disabled_by_default: false
    isee_sensor:
      name: ISEE Sensor
      disabled_by_default: true
    stage_sensor:
      name: Stage
      entity_category: diagnostic
      disabled_by_default: false
    sub_mode_sensor:
      name: Sub Mode
      entity_category: diagnostic
      disabled_by_default: false
    auto_sub_mode_sensor:
      name: Auto Sub Mode
      entity_category: diagnostic
      disabled_by_default: false
    input_power_sensor:
      name: Input Power
      disabled_by_default: false
    kwh_sensor:
      name: Energy Usage
      disabled_by_default: false
#    hardware_settings:
#      update_interval: 20s
#      list:
        # Code 101: Auto Restart
#        - code: 101
#          name: "01-Auto Restart after Power Failure"
#          icon: "mdi:restart"
#          options:
#            1: "ON (Default)"
#            2: "OFF"

        # Code 102: Temperature Sensing Source
        # Important for remote temperature control!
#        - code: 102
#          name: "02-Temperature Source"
#          icon: "mdi:thermometer-check"
#          options:
#            1: "Indoor Unit (Default)"
#            2: "Remote Controller"
#            3: "External (CN105/WiFi)"

        # Code 103: Ventilation / Lossnay interaction
#        - code: 103
#          name: "03-Ventilation Link"
#          options:
#            1: "None (Default)"
#            2: "With Lossnay"
#            3: "Forced"

        # Code 104: Power Voltage
#        - code: 104
#          name: "04-Auto Energy Saving"
#          options:
#            1: "240V (230V) (Default)"
#            2: "220V (208V)"

        # Code 107: Filter Sign Interval
#        - code: 107
#          name: "07-Filter Sign Interval"
#          icon: "mdi:air-filter"
#          options:
#            1: "100 Hours (Default)"
#            2: "2500 Hours"
#            3: "No Indication"

        # Code 108: Ceiling Height / Static Pressure
#        - code: 108
#          name: "08-Ceiling Height Mode"
#          icon: "mdi:arrow-expand-vertical"
#          options:
#            1: "Standard"
#            2: "High Ceiling (Default)"
#            3: "Low Ceiling"

        # Code 110: Auto Mode Switching Logic
#        - code: 110
#          name: "Auto Mode Logic"
#          icon: "mdi:sync"
#          options:
#            1: "Energy Saving (Default)"
#            2: "Comfort / Performance"

        # Code 111: Heater Control
#        - code: 111
#          name: "11-HeaterControl"
#          options:
#            1: "Standard (Default)"
#            2: "Type 1"
#            3: "Type 2"

        # Code 117: Defrost Control
#        - code: 117
#          name: "Defrost Logic"
#          icon: "mdi:snowflake-melt"
#          options:
#            1: "Standard (Default)"
#            2: "High Humidity / Frequent"

        # Code 124: Heating Temperature Offset
#        - code: 124
#          name: "Heating Offset (+2°C)"
#          options:
#            1: "ON (Default)"
#            2: "OFF"

        # Code 125: Fan behavior during Thermo-OFF (Heating)
#        - code: 125
#          name: "Fan during Thermo-OFF (Heat)"
#          icon: "mdi:fan-off"
#          options:
#            1: "Extra Low (Default)"
#            2: "Stop"
#            3: "Set Speed"

        # Code 127: Fan behavior during Thermo-OFF (Cooling)
#        - code: 127
#          name: "Fan during Thermo-OFF (Cool)"
#          icon: "mdi:fan-off"
#          options:
#            1: "Set Speed (Default)"
#            2: "Stop"

        # Code 128: System Error Display
 #       - code: 128
 #         name: "Error Display on Remote"
 #         options:
 #           1: "ON (Default)"
 #           2: "OFF"

[echavet]

Hi @markfen88, thanks for the detailed report!

I've looked into the code to explain what you're seeing. Both behaviors are expected protocol limitations of the Mitsubishi CN105 serial interface.

---

1. Remote Temperature — 0.5°C Resolution

The remote temperature is encoded into 2 bytes using this formula (source):

float temp = round(remoteTemperature_ * 2);
packet[7] = (uint8_t)(temp - 16);   // Encoding A (legacy)
packet[8] = (uint8_t)(temp + 128);  // Encoding B (half-degree)

The round(temp * 2) operation means the best resolution is 0.5°C — this is a hard limit of the Mitsubishi protocol, not something we can improve in software. Your sensor value is rounded to the nearest 0.5°C before being sent to the heat pump.

What the heat pump sees:

Sensor Value	Sent to HP
23.0 – 23.24	23.0°C
23.25 – 23.74	23.5°C
23.75 – 24.24	24.0°C

💡 If you're seeing integer rounding (no .5 values at all), please check that the current_temperature displayed in HA is the room temperature reported back by the HP (which uses its own encoding), not your source sensor. The HP's internal display also rounds to its own resolution.

---

2. Target Temperature — Also Limited to 0.5°C Steps

Regardless of the visual.temperature_step: 0.1 setting in your YAML, the Mitsubishi protocol only supports 0.5°C steps for the target temperature setpoint.

In the code (source):

// When encoding B is active (most modern units):
setting = std::round(2.0f * setting) / 2.0f;  // Rounds to nearest 0.5°C

The visual.temperature_step in ESPHome only controls the UI slider granularity in Home Assistant — it does not change what the heat pump actually accepts. Setting it to 0.1 will let you slide in 0.1° increments, but the value sent to the HP will always be snapped to the nearest 0.5°C.

Recommendation: Set temperature_step to 0.5 to match reality:

visual:
  temperature_step:
    target_temperature: 0.5
    current_temperature: 0.1

---

3. Why Fahrenheit Mode "Helps"

When fahrenheit_compatibility is enabled, the intermediate F↔C conversions create non-aligned fractional values that happen to map to different 0.5°C buckets, giving the illusion of finer control. In reality, the protocol resolution remains 0.5°C — the values just land on different half-degree boundaries.

---

Summary

Feature	Protocol Limit	Can We Improve?
Remote temp resolution	0.5°C	❌ Hardware protocol limit
Target temp step	0.5°C	❌ Hardware protocol limit
Current temp display	0.5°C	❌ HP reports at this resolution

These are fundamental constraints of the CN105 serial protocol — all implementations (SwiCago, native ESPHome, Kumo) share the same limitations.

Hope this helps clarify! Let me know if you have any further questions.

[LeoI5]

❌ Hardware protocol limit

Thank you for the detailed explanation.

Step 0.5 is understandable and cannot be changed, but when controlling the air conditioner through Home Assistant, it is possible to use a generic thermostat and switch the AC mode between cooling and fan-only using scripts. I was able to achieve fairly accurate temperature regulation this way, with a smaller error margin than 0.5°C.

It might be possible to implement a similar algorithm as an optional feature in ESPHome as well.

[markfen88]

Thanks, but remote temperature rounds to the nearest whole, it does NOT do .5