Read energy meters over m-bus

[LaForge]

With my setup I can read two temperature bricklets remotely connected over Modbus RTU using RS485 master extensions bricks and I would like to grab consumption readings off a Kamstrup m-bus meter installed at the same location. I was wondering whether the good chaps at Tinkerforge could give me any pointers on how to interface Modbus to m-bus.

 

The m-bus serial protocol also uses master/slave architecture where the master communicates using voltage modulation and the slaves reply using current modulation. Could I perhaps use a Voltage/Current bricklet to achieve this?

[photron]

According to M-Bus spec you need to detected if the device consumes current (11-20mA, means "0") or not (< 1.5mA, means "1").

 

In principal you could use a Voltage/Current Bricklet or Industrial Dual 0-20mA Bricklet to measure the current consumption of an M-Bus slave interface. But this is limited by the sampling frequency that the Bricklets can achieve. Due to the nature of our communication protocol this is limited to 250Hz. This is probably too low to sample the M-Bus bits. So you probably can't use Bricklets to read data from an M-Bus device.

[LaForge]

Many thanks for your post photron, I will need to look into it in more details.

 

Does the Voltage/Current Bricklet use I2C to communicate with a master brick?

[borg]

Does the Voltage/Current Bricklet use I2C to communicate with a master brick?

 

Yes, we use a INA226 power monitor https://github.com/Tinkerforge/voltage-current-bricklet/raw/master/datasheets/ina226.pdf

[LaForge]

Thank you borg!

 

photron, while learning more about M-Bus I think that the quickest way for me to build something that works is to use an off-the-shelf Modbus to M-Bus interface, so I bought a Hiquel converter. It's based on a Texas Instrument MSP430F1611 mixed signal micro controller. By using a USB to RS485 interface I have already configured this converter to read values off my Kamstrup 401 meter and I can display them with the provided configuration software.

 

Now I want to connect the converter to my existing Tinkerforge Modbus setup. I have been looking at your APIs, is there a way to issue Modbus commands (at application layer level) in order  to read the registers of the converter or is Modbus communication achieved in the firmware of your master bricks?