can2mqtt is a small piece of software written in Go. Its purpose is to be a bridge between a CAN-Bus and a MQTT-Broker. Those are completely different worlds but they have similiaritys in the way they are built. I think i don't have to speak about the differences so i will just pick up the similiarities: In the CAN-world you have so called CAN-Frames. Each CAN-Frame can contain up to eight bytes of payload and CAN-Frame has an ID. In the MQTT-world you have topics and messages. Each message has a specific topic. As you can see it should be possible to map CAN-IDs to MQTT-Topics and their respective payload to messages. That's what this little programm does.

You need to have go installed. After that you should be able to get can2mqtt to run with the following commands:

$ mkdir go
$ export GOPATH=go
$ go get github.com/c3re/can2mqtt

After that you should have a runnable binary under $GOPATH/bin/ called can2mqtt.

The commandline parameters are the following:

can2mqtt -f <can2mqtt.csv> -c <can-interface> -m <mqtt-connectstring> [-v]

Where can2mqtt.csv is the file for the configuration of can and mqtt pairs, can-interface is a socketcan interface and mqtt-connectstring is string that is accepted by the eclipse paho mqtt client. An additional -v flag can be passed to get verbose debug output. Here an example that runs on our Raspberry Pi @c3RE:

can2mqtt -f /etc/can2mqtt.csv -c can0 -m tcp://127.0.0.1:1883

The file can2mqtt.csv has three columns. In the first column you need to specify the CAN-ID as a decimal number. In the second column you have to specify the convert-mode. You can find a list of available convert-modes below. In the last column you have to specify the MQTT-Topic. Each CAN-ID and each MQTT-Topic is allowed to appear only once in the whole file.

Here again the example from the Pi@c3RE:

112,none,huette/all/a03/door/sensors/opened
113,2uint322ascii,huette/all/000/ccu/sensors/time
115,uint322ascii,huette/serverraum/000/filebitch/sensors/ftp_diskusage_percent
116,uint322ascii,huette/all/000/router/sensors/rx_bytes_s
117,uint322ascii,huette/all/000/router/sensors/tx_bytes_s
118,uint322ascii,huette/clubraum/000/ds18b20/sensors/temperatur
119,uint322ascii,huette/all/000/airmonitor/sensors/temp
120,uint322ascii,huette/all/000/airmonitor/sensors/hum
121,uint322ascii,huette/all/000/airmonitor/sensors/airq
122,uint322ascii,huette/all/000/airmonitor/sensors/pm2_5
123,uint322ascii,huette/all/000/airmonitor/sensors/pm10

Explanation for the 1st Line: For example our Doorstatus is published on the CAN-Bus every second with the CAN-ID 112 (decimal). can2mqtt will take everything thats published there and will push it through to mqtt-topic huette/all/a03/door/sensors/opened.

Here they are:

does not convert anything. It just takes a bunch of bytes and hands it over to the other side. If you want to send strings, this will be your choice.

On the can2mqtt way it takes 1, 2, 4 or 8 byte and interprets it as an uint of that size and parses it to a human readable string for the mqtt side. The other way round this convert motde takes an int in a string representation and sends out an array of bytes representing that number (little-endian)

This one is a bit special but all it does is that it takes 8 bytes from the CAN-Bus and parses two uint32s out of it and sends them in a string representation to MQTT. The two numbers are seperated with a simple space(" "). MQTT2CAN-wise it takes two string representations of numbers and converts them to 8 bytes representing them as 2 uint32.

Converts an bytearray of 3 bytes to hexadecimal colorcode

This mode was designed to adress colorized pixels. MQTT-wise you can insert a string like "<0-255> #RRGGBB" wich will be converted to 4 byte on the CAN-BUS the first byte will be the number of the LED 0-255 and bytes 1, 2, 3 are the color of red, green and blue.