OpenEnergyMonitor Community

Problem reading MBUS data with Sontex 531


I have a heatpump monitor which seems to be running correctly except for the most important bit - the MBUS reader. I measure 29v across the terminals but do not see any inputs in Emoncms created as per the setup guide.

I set the firmware for the Sontex:
#define MBUS_ENABLE 1
#define SONTEX_531

Not sure what the address is so set to scan:
byte mbus_address = 0; // Set to 0 for auto scan, (test: check timeout 10ms)

I have also tried the MBUS reader firmware but have not had any luck with that either (no ACK response to any of the commands I try).

Any help appreciated!

Tagging @TrystanLea as resident expert :slight_smile:

Hello @markb

The issue is probably the baud rate. If you try the MBUS reader with both 2400 and 4800 to see if you get any reply that’s probably the first thing to try:

You can usually find the baud rate and address of the unit from the little display on the Sontex unit itself which might be worth trying just so that you know how it is currently configured.

Thanks Trysten, grabbing it from the display is a useful tip. I can see baud rate set to 2400 and address is set to 0. That made me a bit suspicious (setting address to 0 did not work) and digging deeper I think it may not have m-bus enabled - despite me asking for it.

Will need to follow up with the supplier!