ESPHome EM24 Meter Emulator

An ESPHome external component that makes a cheap ESP32 + IR reading head look like a Carlo Gavazzi EM24 Ethernet energy meter over Modbus TCP — so a Victron Cerbo GX / Venus OS device detects it as a native grid meter, no extra drivers or dbus hacks required.

Why?

Victron's ESS (Energy Storage System) needs a grid meter to regulate battery charge/discharge. The officially supported Carlo Gavazzi EM24 costs €200+. If you already have a smart meter with an SML IR interface (common in Germany/Austria), an ESP32 with an IR reading head (~€15) can read the meter data and serve it to the Cerbo GX directly.

How it works

┌──────────────┐   SML/IR    ┌───────────┐  Modbus TCP   ┌──────────┐
│ Smart Meter  │────────────▶│   ESP32   │◀─────────────▶│ Cerbo GX │
│ (e.g. ISKRA) │             │ (ESPHome) │   port 502    │          │
└──────────────┘             └───────────┘               └──────────┘

The ESP32 reads power/energy values via SML over UART, then exposes them as Modbus TCP holding registers that exactly match the EM24's register map. The Cerbo GX auto-detects it (or you add it manually) as a Carlo Gavazzi meter.

Hardware

• ESP32 (any variant — ESP32, ESP32-C3, ESP32-S3, etc.)
• IR reading head with UART/TTL output (e.g. Hichi or Bitshake SmartMeterReader)
• Your smart meter must support SML output via the IR interface

Quick Start

1. Clone or reference this repo

Option A — as a git reference (recommended):

external_components:
  - source:
      type: git
      url: https://github.com/Fexiven/esphome-em24-emulator
      ref: main
    components: [em24_meter]

Option B — local copy:

Copy the components/em24_meter/ folder into your ESPHome config directory.

external_components:
  - source:
      type: local
      path: components
    components: [em24_meter]

2. Configure your YAML

See example.yaml for a full working config. The key part:

em24_meter:
  power: sml_power
  import_energy: sml_import
  export_energy: sml_export
  phases: "1P"

3. Flash and add to Victron

1. Flash the ESP32 with esphome run your_config.yaml
2. On the Cerbo GX go to Settings → Modbus TCP/UDP devices
3. Add the ESP32's IP address, port 502, unit ID 1
4. It should appear as a Carlo Gavazzi EM24 grid meter

Tip: Many Cerbo GX firmware versions also auto-detect Modbus TCP meters on the local network. If auto-scan is enabled the meter may just show up.

Component Configuration

Option	Required	Default	Description
power	yes	—	Sensor ID for grid power in W (positive = import, negative = export)
import_energy	yes	—	Sensor ID for total imported energy in kWh
export_energy	yes	—	Sensor ID for total exported energy in kWh
voltage	no	230 V	Sensor ID for grid voltage (used to synthesize current)
frequency	no	50 Hz	Sensor ID for grid frequency
port	no	502	Modbus TCP listen port
unit_id	no	1	Modbus unit/slave ID
phases	no	"1P"	Phase configuration: "1P", "3P.n", or "3P"
serial	no	"EM24EMU0000001"	Serial number reported to GX (max 14 chars)
invert_power	no	false	Flip the sign of the power value

Adapting to other meter types

This component is not limited to SML meters. Any ESPHome sensor can be wired to the power, import_energy, and export_energy inputs — for example:

• Modbus RTU meters (SDM120, SDM630, etc.) via modbus_controller
• Pulse counters with energy integration
• HTTP/MQTT sensors from other devices
• Template sensors that combine multiple sources

As long as you provide power in W and energy in kWh, the EM24 emulator handles the rest.

Troubleshooting

Cerbo GX doesn't detect the meter:

• Check that the ESP32 is on the same network/VLAN as the Cerbo
• Verify port 502 is reachable: nc -zv <ESP_IP> 502
• Check the ESPHome logs for "EM24 Modbus TCP server listening on port 502"
• Try adding the meter manually on the GX instead of relying on auto-detection

Power values are inverted in Victron:

• Set invert_power: true in the config

Energy values don't update:

• SML meters often report energy in Wh with a scale factor — make sure your sensor filters produce kWh
• Check that state_class: total_increasing is set on your energy sensors

Technical details

The emulator implements the subset of the Carlo Gavazzi EM24 Modbus register map that Victron's dbus-modbus-client (carlo_gavazzi.py) probes during detection and ongoing polling:

• Model ID register 0x000B → returns 1651 (EM24DINAV53XE1X)
• Application register 0xA000 → returns 7 ("H" application type)
• System power 0x0028-0x0029 (s32, ×10)
• Forward energy 0x0034-0x0035 (s32, ×10)
• Reverse energy 0x004E-0x004F (s32, ×10)
• Frequency 0x0033 (u16, ×10)
• L1 voltage/current/power/energy phase block
• Phase config 0x1002, serial 0x5000-0x5006

Supports function codes 0x03 (Read Holding Registers), 0x04 (Read Input Registers), 0x06 (Write Single Register), and 0x10 (Write Multiple Registers).

License

MIT — see LICENSE.