An interface for the Eastron SDM/Modbus smart meter series.
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An HTTP interface to MODBUS smart meters

GoSDM provides an http interface to smart meters with a MODBUS interface. Meter data, i.e. readings, is made accessible through REST API and MQTT. Communication is possible over RS485 connections as well as TCP sockets.

A wide range of DIN-rail meters is supported (see supported sevices).

NOTE Starting with version 0.7 several breaking changes were introduced. See changelog for details.

Table of Contents

Supported Devices

The meters have slightly different capabilities. The EASTRON SDM630 offers a lot of features, while the smaller devices only support basic features. This table gives you an overview (please note: check the manuals for yourself, I could be wrong):

Meter Phases Voltage Current Power Power Factor Total Import Total Export Per-phase Import/Export Line/Neutral THD
SDM120 1 + + + + + + - -
SDM220 1 + + + + + + - -
SDM220 1 + + + + + + - -
SDM530 3 + + + + + + - -
SDM630 v1 3 + + + + + + + +
SDM630 v2 3 + + + + + + + +
Janitza B23-312 3 + + + + + + - -
DZG DVH4013 3 + + - - + + - -
SBC ALE3 3 + + + + + + - -
ABB B-Series 3 + + + + + + + +
SunSpec Inverters 3 + + + + - + - -

Please note that voltage, current, power and power factor are always reported for each connected phase.

  • SDM120: Cheap and small (1TE), but communication parameters can only be set over MODBUS, which is currently not supported by this project. You can use e.g. SDM120C to change parameters.
  • SDM220, SDM230: More comfortable (2TE), can be configured using the builtin display and button.
  • SDM530: Very big (7TE) - takes up a lot of space, but all connections are on the underside of the meter.
  • SDM630 v1 and v2, both MID and non-MID. Compact (4TE) and with lots of features. Can be configured for 1P2 (single phase with neutral), 3P3 (three phase without neutral) and 3P4 (three phase with neutral) systems.
  • Janitza B23-312: These meters have a higher update rate than the Eastron devices, but they are more expensive. The -312 variant is the one with a MODBUS interface.
  • DZG DVH4013: This meter does not provide raw phase power measurements and only aggregated import/export measurements. The meter is only partially implemented and not recommended. If you want to use it: By default, the meter communicates using 9600 8E1 (comset 5). The meter ID is derived from the serial number: take the last two numbers of the serial number (top right of the device), e.g. 23, and add one (24). Assume this is a hexadecimal number and convert it to decimal (36). Use this as the meter ID.
  • SBC ALE3: This compact Saia Burgess Controls meter is comparable to the SDM630: two tariffs, both import and export depending on meter version and compact (4TE). It's often used with Viessmann heat pumps.

Some of my test devices have been provided by B+G E-Tech - please consider to buy your meter from them!


The installation consists of a hardware and a software part. Make sure you buy/fetch the following things before starting:

  • A supported Modbus/RTU smart meter.
  • A USB RS485 adaptor. I use a homegrown one, please see my USB-ISO-RS485 project
  • Some cables to connect the adapter to the SDM630 (for testing, I use an old speaker cable I had sitting on my workbench, for the permanent installation, a shielded CAT5 cable seems adequate)

Hardware installation

SDM630 in my test setup

First, you should integrate the meter into your fuse box. Please ask a professional to do this for you - I don't want you to hurt yourself! Refer to the meter installation manual on how to do this. You need to set the MODBUS communication parameters to 9600 8N1. After this you need to connect a RS485 adaptor to the meter. This is how I did the wiring:

USB-SDM630 wiring

You can try to use a cheap USB-RS485 adaptor, or you can build your own isolated adaptor. I did my first experiments with a Digitus USB-RS485 adaptor which comes with a handy terminal block. I mounted the bias network directly on the terminal block:

bias network

Since then, I tested various adaptors:

  • Supercheap adaptors from China: No ground connection, one worked fine, another one was unstable
  • Industrial adaptors like the Meilhaus RedCOM USB-COMi-SI or the ADAM 4561 isolate the RS-485 bus from the USB line and work extremely reliable. But they are really expensive.

I started to develop my own isolated adaptor. Please check this link for more information.

Software installation

Using the precompiled binaries

You can use the precompiled releases if you like. Just download the right binary for your platform and unzip.

Installing the software from source

You need a working Golang installation, the dep package management tool and Embed in order to compile your binary. Please install the Go compiler first. Then clone this repository:

git clone

If you have make installed you can use the Makefile to install the tools:

$ cd gosdm630
$ make dep
Installing embed tool
Installing dep tool

You can then build the software using the Makefile:

$ make
Generating embedded assets
Generation complete in 109.907612ms
Building for host platform
Created binaries:

As you can see two sets of binaries are built:

  • bin/sdm630_{...} is the software built for the host platform
  • bin/sdm630_{...}-linux-arm is the same for the Raspberry Pi.

If you want to build for all platforms you can use

$ make release

or, for a single platform like the Raspberry Pi binary, use

$ GOOS=linux GOARCH=arm GOARM=5 make build


Now fire up the software:

$ ./bin/sdm630 --help
   sdm - SDM modbus daemon

   sdm630 [global options] command [command options] [arguments...]

     help, h  Shows a list of commands or help for one command

   --serialadapter value, -s value     path to serial RTU device (default: "/dev/ttyUSB0")
   --comset value, -c value            which communication parameter set to use. Valid sets are
                                         1:  2400 baud, 8N1
                                         2:  9600 baud, 8N1
                                         3: 19200 baud, 8N1
                                         4:  2400 baud, 8E1
                                         5:  9600 baud, 8E1
                                         6: 19200 baud, 8E1
                                            (default: 2)
   --device_list value, -d value       MODBUS device type and ID to query, separated by comma.
                                           Valid types are:
                                           "SDM" for Eastron SDM meters
                                           "JANITZA" for Janitza B-Series DIN-Rail meters
                                           "DZG" for the DZG Metering GmbH DVH4013 DIN-Rail meter
                                           Example: -d JANITZA:1,SDM:22,DZG:23 (default: "SDM:1")
   --unique_id_format value, -f value  Unique ID format.
                                           Example: -f Instrument%d
                                           The %d is replaced by the device ID (default: "Instrument%d")
   --verbose, -v                       print verbose messages
   --url value, -u value               the URL the server should respond on (default: ":8080")
   --broker value, -b value            MQTT: The broker URI. ex: tcp://
   --topic value, -t value             MQTT: The topic name to/from which to publish/subscribe (optional) (default: "sdm630")
   --user value                        MQTT: The User (optional)
   --password value                    MQTT: The password (optional)
   --clientid value, -i value          MQTT: The ClientID (optional) (default: "sdm630")
   --rate value, -r value              MQTT: The maximum update rate (default 0, i.e. unlimited) (after a push we will ignore more data from same device andchannel for this time) (default: 0)
   --clean, -l                         MQTT: Set Clean Session (default false)
   --qos value, -q value               MQTT: The Quality of Service 0,1,2 (default 0) (default: 0)
   --help, -h                          show help

A typical invocation looks like this:

$ ./bin/sdm630 -s /dev/ttyUSB0 -d janitza:26,sdm:1
2017/01/25 16:34:26 Connecting to RTU via /dev/ttyUSB0
2017/01/25 16:34:26 Starting API at :8080

This call queries a Janitza B23 meter with ID 26 and an Eastron SDM meter at ID 1. It . If you use the -v commandline switch you can see modbus traffic and the current readings on the command line. At http://localhost:8080 you can see an embedded web page that updates itself with the latest values:

realtime view of incoming measurements

Installation on the Raspberry Pi

You simply copy the binary from the bin subdirectory to the RPi and start it. I usually put the binary into /usr/local/bin and rename it to sdm630. The following sytemd unit can be used to start the service (put this into /etc/systemd/system):

Description=SDM630 via HTTP API
ExecStart=/usr/local/bin/sdm630 -s /dev/ttyAMA0

You might need to adjust the -s parameter depending on where your RS485 adapter is connected. Then, use

# systemctl start sdm630

to test your installation. If you're satisfied use

# systemctl enable sdm630

to start the service at boot time automatically.

WARNING: If you use an FTDI-based USB-RS485 adaptor you might see the Raspberry Pi becoming unreachable after a while. This is most likely not an issue with your RS485-USB adaptor or this software, but because of a bug in the Raspberry Pi kernel. As mentioned there, add the following parameter to your /boot/cmdline.txt:


This switches the internal dwc USB hub of the Raspberry Pi to USB1.1. While this reduces the available USB speed, the device now works reliably.

Detecting connected meters

MODBUS/RTU does not provide a mechanism to discover devices. There is no reliable way to detect all attached devices. The sdm tool when used with the -detect option attempts to read the L1 voltage from all valid device IDs and reports which one replied correctly:

./bin/sdm -detect
2017/06/21 10:22:34 Starting bus scan
2017/06/21 10:22:35 Device 1: n/a
2017/07/27 16:16:39 Device 21: SDM type device found, L1 voltage: 234.86
2017/07/27 16:16:40 Device 22: n/a
2017/07/27 16:16:40 Device 23: n/a
2017/07/27 16:16:40 Device 24: n/a
2017/07/27 16:16:40 Device 25: n/a
2017/07/27 16:16:40 Device 26: Janitza type device found, L1 voltage: 235.10
2017/07/27 16:17:25 Device 247: n/a
2017/07/27 16:17:25 Found 2 active devices:
2017/07/27 16:17:25 * slave address 21: type SDM
2017/07/27 16:17:25 * slave address 26: type JANITZA
2017/07/27 16:17:25 WARNING: This lists only the devices that responded to a known L1 voltage request. Devices with different function code definitions might not be detected.


Rest API

GoSDM provides a convenient REST API. Supported endpoints are:

  • /last/{ID} current data for device
  • /minuteavg/{ID} averaged data for device
  • /status daemon status

Both device APIs can also be called without the device id to return data for all connected devices.

The "GET /last/{ID}"-call simply returns the last measurements of the device with the Modbus ID {ID}:

$ curl localhost:8080/last/11
  "Timestamp": "2017-03-27T15:15:09.243729874+02:00",
  "Unix": 1490620509,
  "ModbusDeviceId": 11,
  "Power": {
    "L1": 0,
    "L2": -45.28234100341797,
    "L3": 0
  "Voltage": {
    "L1": 233.1257781982422,
    "L2": 233.12904357910156,
    "L3": 0
  "Current": {
    "L1": 0,
    "L2": 0.19502629339694977,
    "L3": 0
  "Cosphi": {
    "L1": 1,
    "L2": -0.9995147585868835,
    "L3": 1
  "Import": {
    "L1": 0.16599999368190765,
    "L2": 0.10999999940395355,
    "L3": 0.0010000000474974513
  "TotalImport": 0.2770000100135803,
  "Export": {
    "L1": 0,
    "L2": 0.3019999861717224,
    "L3": 0
  "TotalExport": 0.3019999861717224,
  "THD": {
    "VoltageNeutral": {
      "L1": 0,
      "L2": 0,
      "L3": 0
    "AvgVoltageNeutral": 0

The "GET /minuteavg"-call returns the average measurements over the last minute:

$ curl localhost:8080/minuteavg/11
  "Timestamp": "2017-03-27T15:19:06.470316939+02:00",
  "Unix": 1490620746,
  "ModbusDeviceId": 11,
  "Power": {
    "L1": 0,
    "L2": -45.333974165794174,
    "L3": 0


The /status endpoint provides the following information:

$ curl http://localhost:8080/status
  "Starttime": "2017-01-25T16:35:50.839829945+01:00",
  "UptimeSeconds": 65587.177092186,
  "Goroutines": 11,
  "Memory": {
    "Alloc": 1568344,
    "HeapAlloc": 1568344
  "Modbus": {
    "TotalModbusRequests": 1979122,
    "ModbusRequestRatePerMinute": 1810.5264666764785,
    "TotalModbusErrors": 738,
    "ModbusErrorRatePerMinute": 0.6751319688261972
  "ConfiguredMeters": [
      "Id": 26,
      "Type": "JANITZA",
      "Status": "available"

This is a snapshot of a process running over night, along with the error statistics during that timeframe. The process queries continuously, the cabling is not a shielded, twisted wire but something that I had laying around. With proper cabling the error rate should be lower, though.

Websocket API

Data read from the meters can be observed by clients in realtime using the Websocket API. As soon as new readings are available, they are pushed to connected websocket clients.

The websocket API is available on /ws. All connected clients receive status and meter updates for all connected meters without further subscription.


Another option for receiving client updates is by using the built-in MQTT publisher. By default, readings are published at /sdm/<unique id>/<reading>. Rate limiting is possible.


0.8 (unreleased)

  • Renamed sdm630 command to sdm which also includes sdm_detect now
  • Remove legacy commands. sdm630_logger, sdm630_monitor and sdm630_http are no longer supported. sdm is now the single command provided. The legacy commands are still available in the 0.7 version.
  • Parameters updated:
    • renamed serialadapter to adapter and allow TCP sockets as well
    • renamed device_list to devices
  • Add MODBUS over TCP support
  • Support SunSpec-compatible grid inverters


  • Support Saia Burgess Controls ALE3 meters
  • Implement modbus simulation for testing
  • Various improvements of the web UI
  • Support for go 1.11
  • Improved the README