HONDAe2MQTT

Android app that reads real-time data from a Honda e via OBD-II over Bluetooth and publishes sensor values to an MQTT broker. The app also publishes Home Assistant discovery messages and writes CSV logs to external storage.

Overview

• Connects to a Bluetooth OBD-II adapter (classic Bluetooth, not BLE) and queries the car's CAN bus for live values.
• Publishes selected sensor values to MQTT topics under the hondae topic hierarchy.
• Publishes Home Assistant discovery messages (retained, QoS 1) so sensors are automatically discovered.
• Publishes a heartbeat every 10 seconds and only re-publishes sensor topics when values change to reduce broker load.
• Writes a CSV log file to external storage when a vehicle session is active.

Sensor data published

The app publishes individual sensor topics (examples):

• hondae/status/soc — State of Charge (dash display)
• hondae/status/soc_min — SoC (min)
• hondae/status/soc_max — SoC (max)
• hondae/status/soc_delta — SoC delta (max - min)
• hondae/status/soh — State of Health
• hondae/status/power_kw — Instantaneous power in kW
• hondae/status/current_a — Current in A
• hondae/status/voltage_v — Pack voltage in V
• hondae/status/batt_temp_c — Battery temperature in °C
• hondae/status/ambient_temp_c — Ambient temperature in °C
• hondae/status/is_charging — Boolean flag if charging
• hondae/status/charging_mode — Charging connection type (AC / DC / NC)
• hondae/status/speed_kmh — Speed in km/h
• hondae/status/odo_km — Odometer in km
• hondae/status/aux_bat_v — 12V auxiliary battery voltage
• hondae/gps/lat — GPS latitude
• hondae/gps/lon — GPS longitude
• hondae/gps/elevation_m — GPS elevation (meters)
• hondae/meta/timestamp — Unix timestamp of the data
• hondae/meta/last_can_message — Unix timestamp of the last successful CAN response
• hondae/meta/last_can_message_ago_seconds — Seconds since the last CAN message
• hondae/meta/last_can_fields_csv — CSV list of fields present in the last CAN response
• hondae/heartbeat/status — Heartbeat status (online) published periodically
• hondae/heartbeat/timestamp — Heartbeat timestamp
• hondae/status/bt_connected — Boolean: app connected to the car via Bluetooth
• hondae/status/auto_reconnect_enabled — Boolean: Bluetooth auto-reconnect toggle state
• hondae/status/poll_fast_s, hondae/status/poll_mid_s, hondae/status/poll_slow_s — current poll intervals in seconds

Control topics (MQTT)

The app listens for command topics to control connection and polling intervals:

• hondae/cmd/connect — payloads accepted: 1, 0, true, false, on, off, connect, disconnect, enable, disable
• hondae/cmd/auto_reconnect — same payloads as above; controls the auto-reconnect toggle
• hondae/cmd/poll_fast_s — integer seconds (1–3600)
• hondae/cmd/poll_mid_s — integer seconds (1–3600)
• hondae/cmd/poll_slow_s — integer seconds (1–3600)

Commands are processed by the app and the corresponding state topics under hondae/status/* are updated after changes.

Home Assistant discovery

On MQTT connect the app publishes retained discovery messages for sensors, switches and numbers under homeassistant/.... Discovery payloads include state_topic and command_topic where applicable so Home Assistant can create entities automatically.

How to enter the MQTT broker and credentials

Open the app's Communicate screen and locate the MQTT URL input (the UI also shows a hint like tcp://user:pass@192.168.1.x:1883).

Enter the broker address in one of these formats:

• No authentication: tcp://host:port
• Username only: tcp://username@host:port
• Username and password: tcp://username:password@host:port

Examples:

• tcp://192.168.1.10:1883
• tcp://mqttuser@192.168.1.10:1883
• tcp://mqttuser:secretpassword@mqtt.example.com:1883

Notes:

• Credentials are parsed from the URI only when the URL starts with tcp:// and contains an @ symbol. The substring before the @ is treated as username[:password]. If a colon is present in that substring, the part after the colon is used as password.
• After entering the URL you can press the keyboard's "Done" button (or toggle the Send Data via MQTT switch) to save and (re)connect the MQTT client.

Usage

1. Pair your Bluetooth OBD-II adapter with the Android device (classic Bluetooth, not BLE).
2. Open the app, select the paired device and allow the app to connect.
3. Enable Send Data via MQTT and set the MQTT URL as described above.
4. Optionally allow Bluetooth Auto Reconnect in the UI.
5. Sensor values and heartbeat messages will be published to the broker and Home Assistant will discover available entities automatically.

CSV logging

When a vehicle session begins the app creates a CSV file on external storage. The CSV header is:

sysTimeMs,ODO,SoC (dash),SoC (min),SoC (max),SoH,Battemp,Ambienttemp,kW,Amp,Volt,AuxBat,Connection,Charging,Speed,Lat,Lon

Requirements and known adapters

• Requires a Bluetooth OBD-II adapter with a large message buffer (the app reads long CAN responses). Classic Bluetooth adapters with at least ~864 bytes buffer are recommended.
• Known working adapters: OBDlink MX Bluetooth, vLinker FD, vLinker MC, vLinker BM+, vLinker BM.
• ELM327-clone adapters are known not to work reliably for the Honda e CAN messages.

Disclaimer

This app is provided for testing and experimentation. Use at your own risk. Contributions and pull requests are welcome.

Thanks

This Work is largely based on the Work of ToniH1987s HONDAeInsight and kobius77s HONDAe2MQTT