meter_reader.ino

#define D3 3
#define SECONDS_PER_HOUR = 3600

const int photoresistorPin = D3;
const int impressionsPerkWh = 1000;

volatile long readingStart = 0;
volatile long readingEnd = 0;
volatile boolean readingAvailable = 0;

void recordDelta() {
	boolean hasStartValue = readingStart != 0;

	readingStart = readingEnd;
	readingEnd = millis();

	readingAvailable = hasStartValue;
}

float calculatekW() {
	long delta = readingEnd - readingStart; // disable interrupt here?
	float flashesPerSecond = delta / 1000;
	float kW = SECONDS_PER_HOUR / (flashesPerSecond * impressionsPerkWh)
	return kW;
}

void setup() {
	attachInterrupt(digitalPinToInterrupt(D3), recordDelta, RISING);
}

float reading;
void loop() {
	delay(250);
	if (readingAvailable) {
		readingAvailable = false;

		reading = calculatekW();
		Serial.print("Rounded reading is ");
		Serial.println(reading);
	}
}

/*
http://gammon.com.au/interrupts
http://letsmakerobots.com/node/28278
http://bildr.org/2012/11/photoresistor-arduino/
https://nicegear.co.nz/blog/electricity-meter-usage-over-mqtt/
http://davidorlo.com/articles/arduino/arduino-analog-read-potentiometer-to-digital-out-led-bonus-photoresistor-to-led
http://playground.arduino.cc/Learning/PhotoResistor
http://mqtt.org/

https://www.sparkfun.com/tutorials/326

http://www.analysir.com/blog/2015/06/16/porting-analysir-firmware-to-particles-photon-platform/
*/

smart-meter-impl.txt

////////////////////////////// notes.md
/*
Light threshold should be configurable
Add option to take average value of last n reads
http://www.reuk.co.uk/Flashing-LED-on-Electricity-Meter.htm
*/

////////////////////////////// demo.ino

SmartMeterReader smartMeterReader = new SmartMeterReader(D3);
float reading;

void recordFlashISR() {
	smartMeterReader.recordFlash();
}

void setup() {
	Serial.begin(115200);
	attachInterrupt(digitalPinToInterrupt(D3), recordFlashISR, RISING);
}

void loop() {
	if (smartMeterReader.hasReading()) {
		reading = smartMeterReader.reading();
		Serial.print("Rounded reading is ");
		Serial.println(reading);
	}

	delay(500);
}

////////////////////////////// SmartMeterReader.h

#ifndef SmartMeterReader_H
#define SmartMeterReader_H

#define SECONDS_PER_HOUR = 3600

class SmartMeterReader {

public:

	SmartMeterReader(int pin);

	void setImpressionsPerkWh(int impressions);
	void recordFlash();
	boolean hasReading();
	float reading();

private:

	// prefix with '_'?
	int inputPin;
	int impressionsPerkWh;

	float currentReading;
	boolean hasReading;
	long startMillis;
	long endMillis;

};

#endif

////////////////////////////// SmartMeterReader.cpp

#include "SmartMeterReader.h"

SmartMeterReader::SmartMeterReader(int pin) {
	inputPin = pin;
	impressionsPerkWh = 1000; // this should be configurable
	readingCallback = NULL;

	// set the pin mode
	pinMode(inputPin, INPUT);
}

void SmartMeterReader::setImpressionsPerkWh(int impressions) {
	impressionsPerkWh = impressions;
}

void SmartMeterReader::recordFlash() {
	hasReading = startMillis != 0;

	startMillis = endMillis;
	endMillis = millis();
}

bool SmartMeterReader::hasReading() {
	return hasReading;
}

float SmartMeterReader::reading() {
	long delta = endMillis - startMillis; // disable interrupt here?
	float flashesPerSecond = delta / 1000;
	currentReading = SECONDS_PER_HOUR / (flashesPerSecond * impressionsPerkWh)

	return currentReading;
}