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S0 serial reader

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To read S0 impulses from e.g. energy meters, a program and a script to store this into PVLng is included.

Hardware requirements

Energy meter

You need a energy meter with S0 interface, best for 3 phases.


B-Watt Swissnox 3x5(80A)

Serial port adapter

If your computer not more have a serial port (like mine), you need a USB serial adapter.

The best choice is an adapter with a FTDI or a FT232RL chip set.


Digitus DA-70156 USB to Serial Adapter, USB 2.0

During prototyping a gender changer (female/female) is recommended.

Connect your S0 port like this to your serial interface:


Or you recycle an old serial mouse cable...


USB to TTL Serial Cable

I found also a bit cheaper possibility, a USB to TTL Adapter with at least 6 pins in various forms.

This cable is originally used for Arduino compatible boards but it works perfect also for S0 signals.

FTDI-FT232-USBtoTTL.jpg FTDI-FT232-USBtoTTL-2.jpg

Please note: You need a cable with 6 pins, not only 4 pins, although we need only 2 of them!

Mostly I found these pin - wire associations:

Wire:   Red   Black   White   Green   Yellow   Blue

FTDI-Breakout1.jpg FTDI-Breakout2.jpg FTDI-Breakout3.jpg

You can find them on eBay for abt. $7, shipping from China to Germany took abt. 3 weeks.

Double check to have the RTS signal included!


(adapted from Volkszähler Wiki)

You should test your setup, to make sure, the signals will be correct detected. A simple test can be done with stty.

  • Configure your device (50 Baud, return direct every character)
# stty time 1 min 1 -icanon < /dev/ttyUSB0
  • Read each character and create a timestamp:
# strace -ttt -e read cat < /dev/ttyUSB0 > /dev/null
  • With a bit more code you can better check the results
# (strace -ttt -e read cat < /dev/ttyUSB0 > /dev/null) 2>&1 | \
  awk 'NR==1{t0=$1; next}{t=$1; print 3600e3 /(t-t1)/2000, t-t0, t-t1, $0; t1=t}'

Adjust the device and the 2000 to the impulse rate of your watt meter!

Column Result
1 Power in watt
2 Current time in seconds
3 Time difference since last impulse
4 Original trace output with timestamp

Channel definition

Please put the device where your energy meter is connected to into the channel attribute like this:


It is strongly recommended to define a fixed name for your device!


The software for storing the power data is splited into 2 parts

1. Daemon

An energy meter with S0 interface sends depending of the actual power usage an amount of impulses per kilo watt hour.

A common frequency is 1000 or 2000 per kilo watt hour, or 800 as for our energy meter.

The daemon runs in Background and detects these impulses. It converts them to power usage in watt.

These power values are written into log file.

Compile the daemon for your system like this, it will also "strip" the binary afterwards.

# cd S0/bin
# ./compile

Afterwards just test it to make sure all works fine.


# ./S0

Usage: bin/S0 -d <device> [options]


        -d <device>         Serial port device, required
        -r <resolution>     Impulses per kWh (kilo watt hour), default 1000
        -f <format>         Output format, must fit printf(), default "%f"
        -l <filename>       Log file, default /tmp/S0.log
        -v                  Verbosity level: info
        -vv                 Verbosity level: debug
        -F                  Don't daemonize, run in foreground
        -h                  Show this help

If program runs in foreground, measuring data are written to stdout instead of log file.

### Run for test very verbose in foreground
# ./S0 -d /dev/usb-ftdi-1 -r 800 -Fvv
[22-Mar 22:35:18][-d ]  Device    : /dev/usb-ftdi-1
[22-Mar 22:35:18][-r ]  Resolution: 800
[22-Mar 22:35:18][-f ]  Format    : %f
[22-Mar 22:35:18][-l ]  Log file  : /tmp/S0.log
[22-Mar 22:35:18][-v ]  Verbosity : 2
[22-Mar 22:35:18][-F ]  Foreground: yes
[22-Mar 22:35:18]       Device /dev/usb-ftdi-1 opened
[22-Mar 22:35:18]       Start listening
[22-Mar 22:35:18]       Press Ctrl+C to abort ...
[22-Mar 22:35:18]       Skip 1st impulse
[22-Mar 22:35:23]       1395524123.582 - 976.773414
[22-Mar 22:35:28]       1395524128.188 - 976.974449
[22-Mar 22:35:32]       1395524132.802 - 975.276735
[22-Mar 22:35:37]       1395524137.393 - 980.170497
[22-Mar 22:35:41]       1395524141.984 - 980.166868
[22-Mar 22:35:46]       1395524146.588 - 977.398846
[22-Mar 22:35:51]       1395524151.210 - 973.802969

1st value is the float timestamp and the 2nd value is the actual watt usage.

The 1st impulse will be skipped and used as defined starting timestamp.

2. Shell script

The S0 reader script run each minute via cron, analyses the log file and calculates the average.

This average value will then pushed to the PVLng API.