MBusinoLib - an Arduino M-Bus Decoder Library

Documentation

The MBusinoLib library enables Arduino devices to decode M-Bus (Meterbus) RSP_UD telegrams. (Answer from Slave to Master with data records)

Most M-Bus devices should be supported.

Tested at ESPs, Arduino MKR and Uno R4.

Live test of the MBusinoLib Example at wokwi.com

A working M-Bus --> MQTT gateway with this library MBusino

Credits

MBusinoLib based at the AllWize/mbus-payload library but with much more decode capabilities. mbus-payload's encode capabilities are not supported.

Thanks to AllWize! for the origin library https://github.com/allwize/mbus-payload

Thanks to HWHardsoft and TrystanLea for the M-Bus communication for MBusino: https://github.com/HWHardsoft/emonMbus and https://github.com/openenergymonitor/HeatpumpMonitor

Class: MBusinoLib

Include and instantiate the MBusinoLib class. The constructor takes the size of the allocated buffer.

#include <MBusinoLib.h>

MBusinoLib payload(uint8_t size);

• uint8_t size: The maximum payload size to send, e.g. 254

Decoding

Method: decode

Decodes payload of a whole M-Bus telegram as byte array into a JsonArray (requires ArduinoJson library). The result is an array of objects. The method call returns the number of decoded fields or 0 if error.

uint8_t decode(uint8_t *buffer, uint8_t size, JsonArray& root);

same line from the example

uint8_t fields = payload.decode(&mbus_data[Startadd], packet_size - Startadd - 2, root); 

Example JSON output:

[
{
    "value_scaled": 22.06,
    "units": "C",
    "name": "external_temperature_min"
  },
]

Example extract the JSON

      for (uint8_t i=0; i<fields; i++) {
        const char* name = root[i]["name"];
        const char* units = root[i]["units"];           
        double value = root[i]["value_scaled"].as<double>(); 
        const char* valueString = root[i]["value_string"];   

        //...send or process the Values
      }

possible contained records

only contained records will be sended

• ["code"] contains the library internal code of the VIF
• ["value_scaled"] contains the value of the record as 64 bit real
• ["value_string"] contains the value of the record as ASCII string (only for Time/Dates and special variable lengs values)
• ["units"] contains the unit of the value as ASCII string
• ["name"] contains the name of the value as ASCII string incl. the information of the function field (min, max, err or nothing for instantaneous)
• ["subUnit"] countains the transmitted sub unit
• ["storage"] countains the transmitted storage number
• ["tariff"] countains the transmitted tariff

There are more records available but you have to delete the out comment in the library.

• ["vif"] contains the VIF(E) as HEX in a string.
• ["scalar"] contains the scalar of the value
• ["value_raw"] contains the raw value

Method: getError

Returns the last error ID, once returned the error is reset to OK. Possible error values are:

• MBUS_ERROR::NO_ERROR: No error
• MBUS_ERROR::BUFFER_OVERFLOW: Buffer cannot hold the requested data, try increasing the buffer size. When decoding: incomming buffer size is wrong.
• MBUS_ERROR::UNSUPPORTED_CODING: The library only supports 1,2,3 and 4 bytes integers and 2,4,6 or 8 BCD.
• MBUS_ERROR::UNSUPPORTED_RANGE: Couldn't encode the provided combination of code and scale, try changing the scale of your value.
• MBUS_ERROR::UNSUPPORTED_VIF: When decoding: the VIF is not supported and thus it cannot be decoded.
• MBUS_ERROR::NEGATIVE_VALUE: Library only supports non-negative values at the moment.

uint8_t getError(void);

Home Assistant

The returned units are Home Assistant compatible. There are two methods to get the right device- and state-classes for use as Home Assistant sensor.

const char* getDeviceClass(uint8_t code);

const char* getStateClass(uint8_t code);

References

• The M-Bus: A Documentation Rev. 4.8 - Appendix
• Dedicated Application Layer (M-Bus) by H. Ziegler

License

The MBusinoLib library is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

The MBusinoLib library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with the MBusinoLib library. If not, see http://www.gnu.org/licenses/.