esphome-sml-reader

Language: English | Deutsch

Read your electricity meter via its infrared (IR) interface — no wiring into mains required.
Uses an ESP32-C3 with OLED display (ABRobot 0.42") and a BPW40 photodiode to receive SML data from an ISKRA smart meter. Values are pushed to Home Assistant over WiFi.

Requirement: Unlock the meter's IR diode first. Enter the PIN on the meter front (per your utility instructions) so the IR LED turns on and detailed SML data becomes available.

Features

• Real-time power (W) — import and export
• Total energy counters (kWh) — grid import & grid export
• Tiny OLED display — cycles through current power, import total, export total
• Blue LED — blinks when data is being received
• Web dashboard — built-in on port 80
• OTA updates — flash new firmware over WiFi

ESPHome Web UI

What You Need

Part	Notes
ESP32-C3 OLED board (ABRobot 0.42")	Has a built-in 72×40 SSD1306 display
BPW40 photodiode	Receives the IR signal from the meter
1 kΩ resistor	Pull-down for the photodiode signal
3D-printed case + magnet holder	Optional, but recommended for a clean install
Neodymium magnet (5 mm ⌀ × 3 mm)	Holds the case on the meter
USB-C cable + power supply	Powers the ESP32 inside the meter cabinet

Parts Overview

Left to right: 3D-printed magnet holder, case with light-tight compartment for the photodiode, BPW40 + resistor on Dupont wires, ESP32-C3 ABRobot board.

Assembled Unit

The ESP32-C3 sits in the 3D-printed case. The OLED display and USB-C port are accessible from the front.

Wiring Diagram

The BPW40 photodiode is connected to the ESP32-C3 with just three wires and one resistor:

graph LR
    subgraph "BPW40 Photodiode"
        K["Cathode (short leg)"]
        A["Anode (long leg)"]
    end

    subgraph "ESP32-C3 (ABRobot)"
        V3["3.3V"]
        RX["GPIO20 / RX"]
        GND["GND"]
    end

    R["1 kΩ Resistor"]

    K -- "purple wire" --> V3
    A -- "white wire" --> RX
    RX --> R
    R --> GND

Loading

Key point: The photodiode is reverse-biased (cathode → 3.3V). The 1 kΩ resistor pulls GPIO20 to GND. When the meter's IR LED pulses, the photodiode conducts and the voltage on GPIO20 changes — the ESP32 UART reads this as serial SML data.

Installation

1. Flash the firmware
   Copy esphome_smartmeter_en.yaml (or _de.yaml for German) into your ESPHome dashboard and add your WiFi credentials to secrets.yaml:

   wifi_ssid: "YourNetwork"
   wifi_password: "YourPassword"

2. Wire the photodiode
   Connect the BPW40 as shown in the wiring diagram above.

3. Prepare the 3D-printed case
   Depending on your printer and filament, the holes for the photodiode legs may be too tight. You might need to drill them out — a 3 mm drill bit worked well in my case.

4. Mount on the meter
   Press the neodymium magnet (5 mm ⌀ × 3 mm) into the holder. Place the photodiode directly over the meter's IR interface. It must be light-tight — use the 3D-printed case or black tape. The magnet snaps the unit onto the meter housing.

5. Power up
   Plug in the USB-C cable. The display will show "Waiting…" until the first SML telegram arrives (usually within a few seconds).

6. Add to Home Assistant
   The device will be auto-discovered via the ESPHome integration. You get three sensors:

   • Current Power (W)
   • Grid Import Total (kWh)
   • Grid Export Total (kWh)

Tip: Smart meter cabinets are often metal and shield WiFi. Make sure the ESP32 gets a reliable signal

Installed on the Meter

The reader sits next to the ISKRA meter in the cabinet. The OLED shows the current power draw (483 W in this photo). The blue LED confirms active data reception.

Display Pages

The OLED cycles automatically every 5 seconds:

Page	Label	Value
1	CURR	Current power in W
2	IMPORT	Total grid import in kWh
3	EXPORT	Total grid export in kWh

Compatibility

Tested with ISKRA smart meters using the SML protocol over IR. Should work with any SML-capable meter — you may need to adjust the OBIS codes in the YAML config for your specific meter model.

Contributing

Contributions, issues, and feature requests are welcome! Feel free to open an issue or submit a pull request.

License

This project is open source and available under the MIT License.

Disclaimer

This project is provided as-is, without any warranty of any kind, express or implied. Use it at your own risk. The author assumes no liability for any damage to hardware, software, or property, nor for any personal injury resulting from the use of this project. Always follow local electrical safety regulations when working near your meter cabinet.