DIY or Buy Your S0tool

Choose the approach that fits you best: build your own S0tool from affordable, off-the-shelf components, or order a fully assembled PCB from the Huizebruin shop. Both options give you a local, ESPHome-compatible water and energy meter for Home Assistant.

Build It Yourself

Use a Wemos D1 Mini (ESP8266) with a 5V NPN proximity sensor and a 10KΩ resistor — total cost under €10. Perfect for DIY enthusiasts and hobbyists.

  1. Connect one end of the 10KΩ resistor to 5V.
  2. Connect the other end to D2.
  3. Attach D2 to the signal wire of the NPN sensor.
  4. Connect the sensor's GND wire to GND.
Note: Compatible only with Wemos D1 Mini V1 or V3.0 (ESP8266). You will also need a USB cable and 5V/1A power adapter.
Minimum ESPHome: 2026.1.x — Minimum Home Assistant: 2026.1.x

Shopping List

Part Where to Buy
Wemos D1 Mini (ESP8266) AliExpress · Amazon
NPN Proximity Sensor (5V) AliExpress · Amazon · Opencircuit (NL)
10KΩ Resistor AliExpress · Amazon · Opencircuit (NL)
USB Cable + 5V Adapter Any Micro-B phone charger

Wiring Schematic

S0tool DIY Wiring Diagram

Click image to enlarge

Buy a Ready-Made S0tool

Skip soldering and order a fully assembled S0tool PCB. Comes with the 10KΩ resistor pre-installed. Shipping currently available to Netherlands, Belgium, Germany, and Estonia. For other countries, contact us by email.

Order from Huizebruin Shop

kWh Meter Integration

  1. Ensure your kWh meter has an S0 output port.
  2. Connect a 10KΩ resistor between GND and D5.
  3. Connect 5V to port 20 of the S0 terminal.
  4. Connect D5 to port 21 of the S0 terminal.
S0 kWh Connection S0tool kWh Ready