A HTTP interface to the SDM630-MODBUS smart meter

This project provides a http interface to the Eastron SDM630 smart meter. The device comes in many flavour - make sure to get the "MODBUS" version. The SDM630-MODBUS exposes all measured values over an RS485 connection, making it very easy to integrate it into your home automation system.

How does it look like in OpenHAB?

I use OpenHAB to record various measurements at home. In the classic ui, this is how one of the graphs looks like:

Everything is in German, but the "Verlauf Strombezug" graph shows my power consumption for three phases. I have a SDM630 installed in my distribution cabinet. A serial connection links it to a Raspberry Pi (RPi). This is where this piece of software runs and exposes the measurements via a RESTful API. OpenHAB connects to it and stores the values, just as it does with other sensors in my home.

Installation

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

• A SDM630 smart meter, the MODBUS version.
• A USB RS485 adaptor. Mine is from Digitus.
• 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)
• Two 120 Ohm and two 680 Ohm resistors (1/4W metal).

Hardware installation

First, you should integrate the SDM630 into your fuse box. Please ask a professional to do this for you - I don't want you to hurt yourself! Refer to the SDM630 installation manual on how to do this. You need to set the MODBUS communication parameters to 9600 8N1. I obtained my SDM630 from the German distributor B+G E-Tech.

After this you need to connect the USB adaptor to the SDM630. This is how I did the wiring:

I got this Digitus USB-RS485 adaptor which comes with a handy terminal block. I mounted the bias network directly on the terminal block:

Installing the software from source

You need a working Golang installation and the GB build tool in order to compile your binary. Please install the Go compiler first. Afterwards you can install GB like this:

go get github.com/constabulary/gb/...

Clone this repository:

git clone https://github.com/gonium/gosdm630.git

and build it:

cd gosdm630
gb build all

Now, there should be a binary in the bin subfolder.

Testing

Now fire up the software:

./bin/sdm630_httpd -d /dev/ttyUSB1 -u localhost:8080 -v
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 00 00 02 71 cb
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 43 6b d7 3d 01 fd
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 02 00 02 d0 0b
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 00 00 00 00 fb 84
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 04 00 02 30 0a
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 00 00 00 00 fb 84
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 06 00 02 91 ca
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 00 00 00 00 fb 84
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 08 00 02 f0 09
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 00 00 00 00 fb 84
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 0a 00 02 51 c9
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 00 00 00 00 fb 84
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 0c 00 02 b1 c8
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 00 00 00 00 fb 84
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 0e 00 02 10 08
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 00 00 00 00 fb 84
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 10 00 02 70 0e
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 00 00 00 00 fb 84
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 1e 00 02 11 cd
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 3f 80 00 00 f6 78
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 20 00 02 70 01
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 3f 80 00 00 f6 78
RTUClientHandler: 2015/11/06 12:22:14 modbus: sending 01 04 00 22 00 02 d1 c1
RTUClientHandler: 2015/11/06 12:22:14 modbus: received 01 04 04 3f 80 00 00 f6 78
T: 2015-11-06T12:22:14+01:00 - L1: 235.84V 0.00A 0.00W 1.00cos | L2: 0.00V 0.00A 0.00W 1.00cos | L3: 0.00V 0.00A 0.00W 1.00cos

If you use the -v commandline switch you can see modbus traffic and the current readings on the command line. If you visit http://localhost:8080 you should also see the last received value printed as ASCII text:

Last measurement taken Thursday, 12-Nov-15 14:18:10 CET:
+-------+-------------+-------------+-----------+--------------+--------------+--------------+
| PHASE | VOLTAGE [V] | CURRENT [A] | POWER [W] | POWER FACTOR | IMPORT [KWH] | EXPORT [KWH] |
+-------+-------------+-------------+-----------+--------------+--------------+--------------+
| L1    |      235.17 |        0.19 |     45.83 |         1.00 |         0.74 |         0.01 |
| L2    |        0.00 |        0.00 |      0.00 |         1.00 |         0.00 |         0.00 |
| L3    |        0.00 |        0.00 |      0.00 |         1.00 |         0.00 |         0.00 |
| ALL   | n/a         |        0.19 |     45.83 | n/a          |         0.74 |         0.01 |
+-------+-------------+-------------+-----------+--------------+--------------+--------------+

Crosscompiling e.g. for Raspberry Pi

Go has very good crosscompilation support. Typically, I develop under Mac OS and crosscompile a binary for my RPi. It is easy:

# clear whatever old binaries I have
rm -rf pkg bin
# start crosscompilation
GOOS=linux GOARCH=arm GOARM=5 gb build all

You can then 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_httpd. The following sytemd unit can be used to start the service (put this into /etc/systemd/system):

[Unit]
Description=SDM630 via HTTP API
After=syslog.target
[Service]
ExecStart=/usr/local/bin/sdm630_httpd -d /dev/ttyAMA0
Restart=always
[Install]
WantedBy=multi-user.target

You might need to adjust the -d 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.

OpenHAB integration

The API consists of two calls that return a JSON array. The "GET /last"-call simply returns the last measurements retrieved:

$ curl localhost:8080/last
{"Timestamp":"2015-11-12T15:51:00.297722068+01:00","Power":{"L1":0,"L2":0,"L3":0},"Voltage":{"L1":232.97672,"L2":0,"L3":0},"Current":{"L1":0,"L2":0,"L3":0},"Cosphi":{"L1":1,"L2":1,"L3":1},"Import":{"L1":0.746,"L2":0,"L3":0},"Export":{"L1":0.011,"L2":0,"L3":0}}

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

$ curl localhost:8080/minuteavg
{"Timestamp":"2015-11-12T15:52:14.560779127+01:00","Power":{"L1":0,"L2":0,"L3":0},"Voltage":{"L1":233.11012,"L2":0,"L3":0},"Current":{"L1":0,"L2":0,"L3":0},"Cosphi":{"L1":1,"L2":1,"L3":1},"Import":{"L1":0,"L2":0,"L3":0},"Export":{"L1":0,"L2":0,"L3":0}}

It is very easy to translate this into OpenHAB items. I run the SDM630 software on a Raspberry Pi with the IP 192.168.1.44. My items look like this:

Group Power_Chart
Number Power_L1 "Strombezug L1 [%.1f W]" <power> (Power, Power_Chart) { http="<[http://192.168.1.44:8080/last:60000:JS(SDM630GetL1Power.js)]" }

I'm using the http plugin to call the /last endpoint every 60 seconds. Then, I feed the result into a JSON transform stored in SDM630GetL1Power.js. The contents of transform/SDM630GetL1Power.js looks like this:

JSON.parse(input).Power.L1;

Just repeat these lines for each measurement you want to track. Finally, my sitemap contains the following lines:

Chart item=Power_Chart period=D refresh=1800

This draws a chart of all items in the Power_Chart group.