emu2mqtt

Export real-time energy data from a Rainforest Automation EMU-2 electricity monitor to an MQTT broker — ready to consume in Home Assistant, Node-RED, or any MQTT client.

The EMU-2 pairs with your utility smart meter over Zigbee and presents itself to the host as a USB serial device. This script reads the EMU's XML message stream, decodes the instantaneous demand and cumulative meter readings, and republishes them as simple MQTT topics.

What it publishes

All topics are prefixed with the root topic (--mqtt_topic, default emu2mqtt):

Topic	Meaning	Units
<root>/lwt	Connection status — online / offline (retained, MQTT Last Will)	—
<root>/demand	Instantaneous power draw (negative = exporting to grid)	Watts
<root>/reading	Net cumulative meter reading (delivered − received)	kWh
<root>/readingd	Cumulative energy delivered to you	kWh
<root>/readingr	Cumulative energy received from you (e.g. solar export)	kWh
<root>/price	Current price reported by the meter (only if price data is enabled)	$/kWh

Each value is published only when the EMU reports a newer timestamp than the last one sent, so the broker isn't spammed with duplicates. The lwt topic lets Home Assistant mark the sensors unavailable if the bridge goes offline.

How it works

• emu2mqtt.py — the bridge: connects to MQTT, reads decoded values from the EMU object, and publishes them in a loop. Resilient to broker / Home Assistant restarts — it keeps reconnecting and resumes publishing automatically.
• emu.py — a serial driver for the EMU-2 (based on Rainforest's Emu-Serial-API). Runs a background thread that reads the device's XML output and exposes the latest InstantaneousDemand, CurrentSummationDelivered, PriceCluster, etc.
• api_classes.py — lightweight classes the XML blocks are parsed into.

Requirements

• Python 3
• An EMU-2 connected over USB and paired with your smart meter
• An MQTT broker (e.g. Mosquitto, or the Home Assistant Mosquitto add-on)

Install dependencies:

pip install -r requirements.txt

Usage

python3 emu2mqtt.py \
    --mqtt_server 192.168.50.178 \
    --mqtt_port 1883 \
    --mqtt_username pub \
    --mqtt_password mqttpub \
    --serial_port ttyACM0

Options

Flag	Default	Description
--mqtt_server	192.168.50.178	MQTT broker host
--mqtt_port	1883	MQTT broker port
--mqtt_username	pub	MQTT username
--mqtt_password	mqttpub	MQTT password
--mqtt_client_name	emu2mqtt	MQTT client ID
--mqtt_topic	emu2mqtt	Root topic for all published values
--mqtt_qos	0	MQTT QoS level
--serial_port	ttyACM0	Serial device the EMU-2 enumerates as (Linux: under /dev/, e.g. ttyACM0; Windows: a COM port number)

On Linux the EMU-2 usually appears as /dev/ttyACM0. Check dmesg or ls /dev/ttyACM* after plugging it in. Run as a systemd service to keep it alive across reboots.

Home Assistant example

Once the bridge is publishing, add MQTT sensors:

mqtt:
  sensor:
    - name: "Home Power Demand"
      state_topic: "emu2mqtt/demand"
      unit_of_measurement: "W"
      device_class: power
      availability_topic: "emu2mqtt/lwt"
    - name: "Home Energy Meter"
      state_topic: "emu2mqtt/reading"
      unit_of_measurement: "kWh"
      device_class: energy
      state_class: total_increasing
      availability_topic: "emu2mqtt/lwt"

Attribution

• This script is derived from the excellent emu2influx project by Alex Baker. Credit for the basic flow of the script and EMU API interaction goes to him.
• This script uses the Emu-Serial-API by Rainforest Automation.