Power Meter Pulse Sensor

written by hek

This sensor counts LED pulses from your house meter and converts it into Watts and accumulated KWh.

Locate the little LED on your meeter and mount the light sensor over it to register the power-consumption rate blinks.

There are a few parameters that need to be tuned for each power meter's pulses/KWh (usually says XXX imp/KWh somewhere on your meter). Set the PULSE_FACTOR in the example sketch to pulses/KWh rating on your meter.

You can also set frequency that your sensor will report the power consumption by updating SEND_FREQUENCY. The default is 3 times per minute (every 20 seconds).

The sensor has two modes of operation:


Use this mode if you power the sensor with a battery. In this mode the sensor will sleep most of the time and only report KWh. Unfortunately the sensor cannot report the current consumption in Watts because the sensor can not track time while sleeping; the elapsed time between two blinks is required to calculate the current consumption in Watts.

SLEEP_MODE = false

In this mode the sensor will not sleep and will report the current consumption in Watts and cumulative KWh to the gateway. This mode requires constant power so you will need to connect the sensor to an electrical outlet.

Wiring Things Up

Start by connecting the radio module.

Sensor Arduino Comment
VCC VCC (3.3 - 5V) Red
DO (digital out) Digital pin 3 (D3) Green

Tune the sensitivity/trigger level by adjusting the trim potentiometer on the sensor board. If you plan to use a TSL250R instead of an LM393, refer to the data sheet below for the pin connections.

When using the LM393 light sensor board and WATTS reading are completely wrong so don't get reported add a 0.1uF capacitor between the DO and GND.


Last updated by tekka007, 24 Jul 2022, "Upate CI and HW defs (#1530)"
   The MySensors Arduino library handles the wireless radio link and protocol
   between your home built sensors/actuators and HA controller of choice.
   The sensors forms a self healing radio network with optional repeaters. Each
   repeater and gateway builds a routing tables in EEPROM which keeps track of the
   network topology allowing messages to be routed to nodes.

   Created by Henrik Ekblad <[email protected]>
   Copyright (C) 2013-2019 Sensnology AB
   Full contributor list: https://github.com/mysensors/MySensors/graphs/contributors

   Documentation: http://www.mysensors.org
   Support Forum: http://forum.mysensors.org

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   version 2 as published by the Free Software Foundation.


   Version 1.0 - Henrik Ekblad
   Version 1.1 - Peter Andersson added millis watt calculation if time between pulses > 1h

   This sketch provides an example how to implement a LM393 PCB
   Use this sensor to measure kWh and Watt of your house meter
   You need to set the correct pulsefactor of your meter (blinks per kWh).
   The sensor starts by fetching current kWh value from gateway.
   Reports both kWh and Watt back to gateway.

   Unfortunately millis() won't increment when the Arduino is in
   sleepmode. So we cannot make this sensor sleep if we also want
   to calculate/report watt value.

// Enable debug prints
#define MY_DEBUG

// Enable and select radio type attached
#define MY_RADIO_RF24
//#define MY_RADIO_NRF5_ESB
//#define MY_RADIO_RFM69
//#define MY_RADIO_RFM95

#include <MySensors.h>

#define DIGITAL_INPUT_SENSOR 3  // The digital input you attached your light sensor.  (Only 2 and 3 generates interrupt!)
#define PULSE_FACTOR 1000       // Number of blinks per kWh of your meter. Normally 1000.
#define SLEEP_MODE false        // Watt value can only be reported when sleep mode is false.
#define MAX_WATT 10000          // Max watt value to report. This filters outliers.
#define CHILD_ID 1              // Id of the sensor child

    20000; // Minimum time between send (in milliseconds). We don't want to spam the gateway.
double ppwh = ((double)PULSE_FACTOR) / 1000; // Pulses per watt hour
bool pcReceived = false;
volatile uint32_t pulseCount = 0;
volatile uint32_t lastBlinkmicros = 0;
volatile uint32_t lastBlinkmillis = 0;
volatile uint32_t watt = 0;
uint32_t oldPulseCount = 0;
uint32_t oldWatt = 0;
double oldkWh;
uint32_t lastSend;
MyMessage wattMsg(CHILD_ID, V_WATT);
MyMessage kWhMsg(CHILD_ID, V_KWH);
MyMessage pcMsg(CHILD_ID, V_VAR1);

#if defined(ARDUINO_ARCH_ESP8266) || defined(ARDUINO_ARCH_ESP32)

void IRQ_HANDLER_ATTR onPulse()
    if (!SLEEP_MODE) {
        uint32_t newBlinkmicros = micros();
        uint32_t newBlinkmillis = millis();
        uint32_t intervalmicros = newBlinkmicros - lastBlinkmicros;
        uint32_t intervalmillis = newBlinkmillis - lastBlinkmillis;
        if (intervalmicros < 10000L && intervalmillis < 10L) { // Sometimes we get interrupt on RISING
        if (intervalmillis < 360000) { // Less than an hour since last pulse, use microseconds
            watt = (3600000000.0 / intervalmicros) / ppwh;
        } else {
            watt = (3600000.0 / intervalmillis) /
                   ppwh; // more thAn an hour since last pulse, use milliseconds as micros will overflow after 70min
        lastBlinkmicros = newBlinkmicros;
        lastBlinkmillis = newBlinkmillis;

void setup()
    // Fetch last known pulse count value from gw
    request(CHILD_ID, V_VAR1);

    // Use the internal pullup to be able to hook up this sketch directly to an energy meter with S0 output
    // If no pullup is used, the reported usage will be too high because of the floating pin

    attachInterrupt(digitalPinToInterrupt(DIGITAL_INPUT_SENSOR), onPulse, RISING);
    lastSend = millis();

void presentation()
    // Send the sketch version information to the gateway and Controller
    sendSketchInfo(F("Energy Meter"), F("1.1"));

    // Register this device as power sensor
    present(CHILD_ID, S_POWER);

void loop()
    uint32_t now = millis();
    // Only send values at a maximum frequency or woken up from sleep
    bool sendTime = now - lastSend > SEND_FREQUENCY;
    if (pcReceived && (SLEEP_MODE || sendTime)) {
        // New watt value has been calculated
        if (!SLEEP_MODE && watt != oldWatt) {
            // Check that we don't get unreasonable large watt value, which
            // could happen when long wraps or false interrupt triggered
            if (watt < ((uint32_t)MAX_WATT)) {
                send(wattMsg.set(watt));  // Send watt value to gw
            oldWatt = watt;

        // Pulse count value has changed
        if (pulseCount != oldPulseCount) {
            send(pcMsg.set(pulseCount));  // Send pulse count value to gw
            double kWh = ((double)pulseCount / ((double)PULSE_FACTOR));
            oldPulseCount = pulseCount;
            if (kWh != oldkWh) {
                send(kWhMsg.set(kWh, 4));  // Send kWh value to gw
                oldkWh = kWh;
        lastSend = now;
    } else if (sendTime && !pcReceived) {
        // No pulse count value received from controller. Try requesting it again.
        request(CHILD_ID, V_VAR1);
        lastSend = now;

    if (SLEEP_MODE) {
        sleep(SEND_FREQUENCY, false);

void receive(const MyMessage &message)
    if (message.getType()==V_VAR1) {
        pulseCount = oldPulseCount = message.getLong();
        Serial.print("Received last pulse count value from gw:");
        pcReceived = true;


NameSize# Downloads
lm2903-n.pdf1.56 MB7580

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