emonMbus

Arduino firmware for a dedicated M-Bus master to submit "BTU" Heat Meter data to Emoncms

This project is not supported or endorsed by the OpenEnergyMonitor project, but is obviously completely dependent on it and heavily based on the project's hardware and software. Thanks go out to those folks for their Open Source work.

Author: Bryan McLellan btm@loftninjas.org

Hardware / Kit

Some assembly required...

• Arduino Uno
• JeeLabs RFM12B Board with a 433/434 MHz
  As far as I can tell, the jeelib library does not support the RFM69HCW (high power) radio but does support the RFM69CW in compatibility mode as a replacement for the possibly deprecated RFM12B. You need a radio supported by jeelib to be able to transmit to an emonBase or emonPi. Modern Devices sells the board in the USA.
• OpenEnergyMonitor m-bus master circuit.
  The circuit used in the OpenEnergyMonitor Heatpump Monitor was based off of Tomas Menzl's libmbus design. The M-Bus master schematic can be best seen as the circuit in the lower right corner of the Heatpump Monitor v4 schematic.
  • D4 and D5 go to the corresponding digital pins on the Arduino
  • 1 and 2 of T9 go to the M-Bus connection of the meter which is polarity independent and does not need terminating resistors like Modbus.
  • The XL6009E1 step-up converter used in the OpenEnergyMonitor design can be acquired through Addicore and provides an adequate 36v that M-Bus desires when fed 5V from the Arduino. The original design and the M-Bus specification call for 36v, I don't know why the OpenEnergyMonitor project has 24v on it's schematic.
  • JP4 - JP7 on the schematic are risers for holding the XL6009E1 and aren't otherwise electrically important.
  • I used a BC557 as a substitute for the BC307 transistor which wasn't readily available.
• Spire Metering Technologies 280T-S Ultrasonic Heat Meter
  The Shenitech/SpireMT 280T appears to be an ancestor of the 280T-S and is likely compatible from the documentation I've seen. The meter is designed to measure consumption but the supply and return sensors can be swapped to measure production.
• Air to Water Heat Pump
  I have one of these.

Resources

• The Meter Bus (M-Bus) documentation is essential
• OpenEnergyMonitor Heatpump Monitor build guide
• The MBUS Reader Arduino firmware is the best place to start to verify your M-Bus master circuit and poke at the meter. I learned a lot about the meter's data format this way.
• I have the SpireMT documentation for their M-Bus slave if you can't get it.

Development

You'll need the CustomSoftwareSerial and jeelib libraries.

OpenEnergyMonitor has been exploring a number of hardware configurations to add an M-Bus master circuit to, from a emonPi replacement to an addon to the emonTx. I decided that this configuration was the best way I could produce firmware that someone else might make use of. There's some refactoring to do to support other meters, but contributions are welcome.

License

The OpenEnergyMonitor firmware is licensed GPLv3, and this is a derivative, so this is as well.

Copyright 2018, Bryan McLellan btm@loftninjas.org

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