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Python (Raspberry Pi · Linux · macOS · Windows)

The WattWächter WiFi/USB — both Gen.2 and Gen.1 — can be read directly with Python over its USB-C interface. When USB data output is enabled, the WattWächter outputs the meter's raw SML data stream (9600 baud, 8N1) over USB-C. The USB cable serves as both power supply and data line.

We use pyserial to read the serial interface and smllib to decode the telegrams.

Works with Gen.2 and Gen.1

The USB data output is identical on both generations — only the way you enable it differs (Gen.2 via software command, Gen.1 via jumper). The example script is the same for both.

Meter prerequisites

For the meter to send the full instantaneous values (power, phases), the PIN usually has to be disabled and the extended info mode (Inf → On) enabled. You get the PIN from your grid operator. See Preparing the meter.

Step 1 — Enable USB data output

How the data is output over USB depends on your WattWächter's generation. You can identify yours from the product overview.

Step 2 — Connect the WattWächter

  1. Place the WattWächter on the meter (on Gen.1, close the housing first)
  2. Connect the WattWächter via the USB-C cable to a free USB port on your computer or Raspberry Pi
  3. The USB cable serves as both power supply and data line

Step 3 — Find the serial port

The WattWächter registers with the operating system as a USB serial device (chip 1a86 / CH340).

ls /dev/ttyUSB*
# e.g. /dev/ttyUSB0

Stable device path

For permanent scripts, use the path under /dev/serial/by-id/... (e.g. /dev/serial/by-id/usb-1a86_USB_Serial-if00-port0). It persists across reboots and USB-port changes — unlike /dev/ttyUSB0.

ls /dev/tty.usbserial*
# e.g. /dev/tty.usbserial-XXXX

Open Device Manager → Ports (COM & LPT). The WattWächter appears as USB-SERIAL CH340 (COMx), e.g. COM3.

Step 4 — Install the libraries

pip install pyserial smllib

Example script

import serial
from smllib import SmlStreamReader

# --- Serial interface -------------------------------------------------------
# Linux / Raspberry Pi:  /dev/ttyUSB0
# macOS:                 /dev/tty.usbserial-XXXX
# Windows:               COM3
PORT = "/dev/ttyUSB0"

# OBIS codes we care about (short form -> label)
OBIS = {
    "1.8.0":  "Consumption",  # Wh, drawn from the grid
    "2.8.0":  "Feed-in",      # Wh, fed into the grid
    "16.7.0": "Power",        # W, current active power (signed)
}

ser = serial.Serial(PORT, baudrate=9600, bytesize=8,
                    parity="N", stopbits=1, timeout=2)
stream = SmlStreamReader()

print(f"Reading WattWächter WiFi/USB on {PORT} ...")
while True:
    data = ser.read(ser.in_waiting or 1)
    if not data:
        continue

    stream.add(data)
    frame = stream.get_frame()
    if frame is None:
        continue   # telegram not yet complete

    for entry in frame.get_obis():
        name = OBIS.get(entry.obis.obis_short)
        if name is None:
            continue
        value = entry.get_value()          # already scaled (value × 10^scaler)
        if entry.obis.obis_short in ("1.8.0", "2.8.0"):
            print(f"{name:12s}: {value / 1000:.3f} kWh")
        else:
            print(f"{name:12s}: {value:.0f} W")
    print("-" * 30)

Example output:

Reading WattWächter WiFi/USB on /dev/ttyUSB0 ...
Consumption : 12345.678 kWh
Feed-in     : 4321.000 kWh
Power       : 437 W
------------------------------

Reading additional values

Extend the OBIS dictionary with more codes (e.g. 36.7.0, 56.7.0, 76.7.0 for the per-phase power or 32.7.0, 52.7.0, 72.7.0 for the per-phase voltages). entry.get_value() returns the value already correctly scaled, and entry.unit holds the unit code. See Further OBIS codes for an overview of common OBIS codes.

Troubleshooting

Problem Possible cause / solution
No /dev/ttyUSB* or no COM port USB data output not enabled (Gen.2: sensor53 u1, Gen.1: jumpers in USB mode); reconnect the USB cable. On Windows, install the CH340 driver if needed
Permission denied on /dev/... Add your user to the dialout group: sudo usermod -aG dialout $USER, then log in again
No data / frame stays None Reading head not positioned correctly over the meter's IR interface; USB data output not active; wrong port
Only energy counters, no power/phases Disable the PIN at the meter and set Inf → On
Values off by a factor of 10/100 In rare cases, replace get_obis() with parse_frame() (see the smllib docs)