Home Energy Monitor

Overview

Split-core current clamps clip around a single wire and measure the current flowing through it, with no cut wires and no contact with live conductors. The ET-S38 reads two SCT-013 clamps with a 16-bit ADC and a built-in burden resistor.

Clip one clamp on your incoming supply and the other on a big load such as the AC. The ESP32 calculates RMS current and estimated power every second.

• Two channels, up to 100 A each
• RMS current and estimated power
• Non-invasive: clamps only, no live connections
• Runs from a 12 V adapter

What you need

ElectroTrical boards

ET-S382-Channel CT Clamp Interface2-channel CT clamp interface with 16-bit ADC

AED 49.00Out of stock

ET-P10Dual-Rail 5 V + 3.3 V Supply12 V → 5 V and 3.3 V supply

AED 49.00Out of stock

Boards total: AED 98.00

These boards are being manufactured. Open a board's page to see when it's back, or ask us about a kit.

You'll also need

• ESP32-S3 DevKitC-1 (or any ESP32-S3 board) with a USB-C data cable. Not sold by ElectroTrical.
• 2 × YHDC SCT-013-000 (100 A : 50 mA) clamps with 3.5 mm plugs
• 12 V DC adapter, 1 A
• Enclosure that mounts next to (not inside) your distribution board

Wiring

Clip each clamp around one conductor only (live or neutral). Around a full cable with both, the currents cancel and read zero. Opening a distribution board is work for a licensed electrician — ask one to fit the clamps if the wires are inside the panel.

Build it

1. 01

   Use the right clamp

   This board is built for the SCT-013-000 current-output clamp (100 A : 50 mA). Voltage-output versions (SCT-013-030 etc.) have their own burden and need the burden jumper changed — check the ET-S38 product page.

2. 02

   Wire on the bench

   Wire the ESP32 and ET-P10 as shown. Test first with the ESP32 on USB and no 12 V adapter.

3. 03

   Set up the Arduino IDE

   Install Arduino IDE 2, add the Espressif ESP32 board package (Boards Manager → “esp32” by Espressif), select “ESP32S3 Dev Module” and turn on USB CDC On Boot so Serial prints over USB. Install the libraries listed above the sketch from Library Manager.

4. 04

   Check with a known load

   Clamp a cable feeding a kettle (≈ 8–10 A at 2 kW). The reading should match the kettle's rating divided by 230 V.

5. 05

   Set your voltage

   UAE supply is 230 V. The sketch multiplies current by MAINS_V to estimate power — it assumes a power factor of 1, so AC units with motors will read slightly high.

6. 06

   Install

   Have the clamps fitted around the live conductor of the incoming supply and the AC circuit. Route the 3.5 mm leads out to the enclosure.

Arduino code

Written for the ESP32-S3 DevKitC-1 with the Espressif Arduino core. Install these libraries from the Arduino Library Manager:

• Adafruit ADS1X15

#include <Wire.h>
#include <Adafruit_ADS1X15.h>

const float MAINS_V   = 230.0;     // UAE nominal
const float CT_RATIO  = 2000.0;    // SCT-013-000: 100 A : 50 mA
const float BURDEN_OHM = 22.0;     // on the ET-S38
const int   SAMPLE_MS = 200;       // 10 cycles at 50 Hz

Adafruit_ADS1115 ads;

float readAmpsRms(int ch) {
  double sumSq = 0;
  int n = 0;
  unsigned long t0 = millis();
  while (millis() - t0 < SAMPLE_MS) {
    int16_t raw = (ch == 1) ? ads.readADC_Differential_0_1()
                            : ads.readADC_Differential_2_3();
    float v = ads.computeVolts(raw);
    sumSq += v * v;
    n++;
  }
  float vRms = sqrt(sumSq / n);
  return vRms / BURDEN_OHM * CT_RATIO;
}

void setup() {
  Serial.begin(115200);
  Wire.begin(8, 9);
  Wire.setClock(400000);
  if (!ads.begin(0x48)) {
    Serial.println("ADS1115 not found (0x48)");
    while (1) delay(100);
  }
  ads.setGain(GAIN_TWO);                    // ±2.048 V
  ads.setDataRate(RATE_ADS1115_860SPS);
}

void loop() {
  float a1 = readAmpsRms(1);
  float a2 = readAmpsRms(2);
  if (a1 < 0.15) a1 = 0;                    // ignore noise floor
  if (a2 < 0.15) a2 = 0;
  Serial.printf("Supply %.2f A (%.0f W) | Circuit 2 %.2f A (%.0f W)\n",
                a1, a1 * MAINS_V, a2, a2 * MAINS_V);
  delay(1000);
}

Troubleshooting

Take it further

• Push the values to Home Assistant with ESPHome's ads1115 + ct_clamp components
• Add a daily kWh counter and an alert when the AC draws unusual current
• Use the ET-S39 3-phase board for villas with three-phase supply