SML to HTTP proxy

This application is designed to read a binary SML stream via TCP/IP and export all values via a simple HTTP REST API using JSON. It is intended to be used with home automation systems to read the values of smart meters. In the most basic configuration, a serial to TCP/IP converter in conjunction with a D0 read head can be used.

Building

To build this application first install Go 1.20 or later. Then run the provided Makefile:

make

This builds multiple binaries:

Path	Usage
bin/smlToHttp-linux-native	Built for the computer building the application
bin/smlToHttp-linux-amd64	Built for a normal desktop computer
bin/smlToHttp-linux-arm64	Built for a computer running the ARM64 architecture, e. g. a Raspberry Pi 4

Feel free to extend the Makefile if your use case is not dealt with.

Usage

First create a configuration file named config.yml. Replace the IP address serial to TCP/IP converter in the meters section. Note: You can add multiple meters, not just one.

To disable the HTTP request log, set web/disable_request_log to true. Similarly, you can disable the SML reception log by setting meters/disable_reception_log to true on a per meter basis.

web:
  address: 127.0.0.1:11123
  disable_request_log: false

meters:
  - id: my_smartmeter
    address: 192.168.0.1:8234
    reconnect_delay: 10
    read_timeout: 5
    connect_timeout: 10
    debug: false
    disable_reception_log: false

Then start the application:

./bin/smlToHttp-native -config config.yml

The log should now yield that the connection is successful and that SML frames are being decoded. You can then try to access the API:

curl http://127.0.0.1:11123/processImage

The response should look something along the lines of:

{
  "meters": {
    "my_smartmeter": {
      "connected": true,
      "lastUpdate": "2023-06-06T13:12:10.064515753Z",
      "values": {
        "1-0:1.8.0*255": {
          "value": 123456.7,
          "unit": 30
        },
        "1-0:2.8.0*255": {
          "value": 234567.8,
          "unit": 30
        },
        "1-0:16.7.0*255": {
          "value": -3210,
          "unit": 27
        },
        "... continued ...": {}
      }
    }
  }
}

The response above has been truncated a bit, but you should get the gist out of it. In the example above, the OBIS key 1-0:1.8.0*255 yields a value of 123456.7, which represents 123456.7 kWh of retrieved energy from the energy provider. Also, we have sold 234567.8 kWh of energy to the service provider. And our current power draw is -3210 W, so we are currently selling 3210 Watts to the service provider. A positive value here would mean that we currently buy energy from the provider. Please refer to your smart meter user manual for exported OBIS items.

Note: Most smart meters will only export basic information via the optical interface when the PIN protection is not deactivated. This is by design, as the currently used power is considered privacy sensitive. To get the full data set, please refer to the manual of your smart meter on how to enable the full data set.

Debugging SML output

When you have a dump of the meter's output in a file, you can decode the file's content using the following command. It will dump every valid SML message in the file. Invalid messages (e.g. CRC does not match or invalid structure) are ignored.

./bin/smlToHttp-native -dump <file>

Integration with OpenHAB

The proxy is currently in production use in combination with OpenHAB, but may of course serve other systems. For this example, the HTTP binding and the JSONPath transformation addons are required. An example configuration might be:

Thing http:url:smlToHttp "SML to HTTP" [
    baseURL="http://127.0.0.1:11123/processImage",
    refresh=2
] {
    Channels:
        Type number : my_smartmeter_1_8_0 "My SmartMeter 1.8.0" [ stateTransformation="JSONPATH:$.meters.my_smartmeter.values.['1-0:1.8.0*255'].value", unit="Wh", mode="READONLY" ]
        Type number : my_smartmeter_2_8_0 "My SmartMeter 2.8.0" [ stateTransformation="JSONPATH:$.meters.my_smartmeter.values.['1-0:2.8.0*255'].value", unit="Wh", mode="READONLY" ]
        Type number : my_smartmeter_16_7_0 "My SmartMeter 16.7.0" [ stateTransformation="JSONPATH:$.meters.my_smartmeter.values.['1-0:16.7.0*255'].value", unit="W", mode="READONLY" ]
}

License

SML to HTTP proxy
Copyright (C) 2023  Stephan Brunner

This program 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.

This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.