MQTT messages

Every topic WiCAN publishes or listens on, with the payload of each. `` is the device id, the twelve lower-case hexadecimal characters of the access point name; the first three topics can be renamed on the MQTT card.

Topics

Topic	Direction	Payload
wican/<id>/can/status	published, retained	{"status": "online"} on connect. The broker publishes {"status": "offline"} (retained, the last will) when the connection drops.
wican/<id>/can/rx	published	Frames received from the bus, in batches (with the RX checkbox on); a CAN filter value {"Name": value} when filter rules exist; the AutoPID values when no destination topic is set.
wican/<id>/can/tx	subscribed (with the TX checkbox on)	Frames to send onto the bus.
wican/<id>/cmd	subscribed, and published	A command in, its answer out, on the same topic.
wican/<id>/elm327	published	The frames the ELM327 interpreter exchanged for an app, with the elm327 log on.
the AutoPID Destination	published, retained	The grouped snapshot of all values, every cycle.
a row's Send_to	published, retained	One value, every time the row is read.
the Alert Topic of the battery alert	published, on the alert broker	The low battery message.

Frames

A batch of received frames, one message per batch; ts is a millisecond counter that wraps every minute, id is decimal:

{"bus":"0","type":"rx","ts":34610,"frame":[
  {"id":123,"dlc":8,"rtr":false,"extd":false,"data":[1,2,3,4,5,6,7,8]},
  {"id":124,"dlc":8,"rtr":false,"extd":true,"data":[1,2,3,4,5,6,7,8]}]}

A frame to send, published to the TX topic (several frames per message are allowed; dlc up to 8, extd true for a 29-bit id, rtr true for a remote frame):

{"bus":"0","type":"tx","frame":[{"id":2015,"dlc":8,"rtr":false,"extd":false,"data":[2,1,70,170,170,170,170,170]}]}

That frame is the OBD-II request for ambient air temperature (service 01, PID 46) to the broadcast id 0x7DF; the engine answers on 0x7E8 (2024), which arrives on the RX topic as {"id":2024,"dlc":8,...,"data":[3,65,70,<value>,...]}, the temperature being the value minus 40. The 29-bit broadcast id is 0x18DB33F1, 417018865 in decimal, with extd true.

The ELM327 log uses the same shape, one frame per message, with type tx for what the interpreter sent and rx for what it received.

AutoPID values

The grouped snapshot, captured from the bench device every 5 seconds:

wican/4831b7854135/autopid {"RPM_custom":716,"Speed_wallbox":173,"0C-EngineRPM":716,"0D-VehicleSpeed":173,"05-EngineCoolantTemp":21}

A row with Destination Type MQTT_Topic, and one with MQTT_WallBox, each on its own Send_to topic, every period of the row:

wican/4831b7854135/rpm {"RPM_custom":716}
wican/4831b7854135/speed 173.00

Values are numbers with up to two decimals; a parameter declared as a binary sensor in a profile is published as "on" or "off".

The CAN filter

Each rule publishes its value on its own cycle to the RX topic, as {"Name": value} with six decimals:

wican/4831b7854135/can/rx {"EngineSpeed": 1165.000000}

Commands

Publish a JSON object to wican/<id>/cmd; the answer comes back on the same topic, so a subscriber sees both:

wican/4831b7854135/cmd {"cmd":"get_vbatt"}
wican/4831b7854135/cmd {"battery_voltage": 11.599999}

Command	Answer	Effect
{"cmd":"get_vbatt"}	{"battery_voltage": 11.599999}	reads the battery voltage
{"cmd":"reboot"}	{"rsp": "ok"}	restarts the device 2 seconds later
{"cmd":"get_autopid_data"}	none on this topic	asks for one AutoPID round when Polling is disabled; the values go to their usual topics

The battery alert

Published once per alert interval to the Alert Topic on the alert broker, with the voltage at the time:

{"alert": "low_battery", "battery_voltage": 11.400000}