TerabullKeith Snyder

Home Power Monitor

This device monitors the total current coming into your home and performs and FFT on it to determine what appliances are running.

IntermediateFull instructions provided4 hours7,985
Home Power Monitor

Things used in this project

Hardware components

Particle Photon
Current Transformer
Resistor 15 Ohm
Resistor 470 Ohm
Breadboard (generic)
Breadboard (generic)
Capacitor 10 µF
Capacitor 10 µF

Software apps and online services

Particle Build Web IDE
Particle Build Web IDE
Google Sheets
Google Sheets


Read more


Voltage Divider Cicuit

Photon Schematic

This is a schematic of how the photon can be wired. You have the option of creating only one voltage divider circuit if you like.


Google Sheets JavaScript

This is the code to put into the Google Sheets Script that runs every night to calculate the total power used by each appliance.
//  1. Enter sheet name where data is to be written below
        var SHEET_NAME = "Sheet1";

//  2. Run > setup
//  3. Publish > Deploy as web app
//    - enter Project Version name and click 'Save New Version'
//    - set security level and enable service (most likely execute as 'me' and access 'anyone, even anonymously)
//  4. Copy the 'Current web app URL' and post this in your form/script action
//  5. Insert column names on your destination sheet matching the parameter names of the data you are passing in (exactly matching case)

var SCRIPT_PROP = PropertiesService.getScriptProperties(); // new property service

// If you don't want to expose either GET or POST methods you can comment out the appropriate function
function doGet(e){
  return handleResponse(e);

function doPost(e){
  return handleResponse(e);

function handleResponse(e) {
  // shortly after my original solution Google announced the LockService[1]
  // this prevents concurrent access overwriting data
  // [1] http://googleappsdeveloper.blogspot.co.uk/2011/10/concurrency-and-google-apps-script.html
  // we want a public lock, one that locks for all invocations
  var lock = LockService.getPublicLock();
  lock.waitLock(30000);  // wait 30 seconds before conceding defeat.

  try {
    // next set where we write the data - you could write to multiple/alternate destinations
    var doc = SpreadsheetApp.openById(SCRIPT_PROP.getProperty("key"));
    var sheet = doc.getSheetByName(SHEET_NAME);

    // we'll assume header is in row 1 but you can override with header_row in GET/POST data
    var headRow = e.parameter.header_row || 1;
    var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
    var nextRow = sheet.getLastRow()+1; // get next row
    var row = [];
    // loop through the header columns
    for (i in headers){
      if (headers[i] == "Timestamp"){ // special case if you include a 'Timestamp' column
        row.push(new Date());
      } else { // else use header name to get data
    // more efficient to set values as [][] array than individually
    sheet.getRange(nextRow, 1, 1, row.length).setValues([row]);
    // return json success results
    return ContentService
          .createTextOutput(JSON.stringify({"result":"success", "row": nextRow}))
  } catch(e){
    // if error return this
    return ContentService
          .createTextOutput(JSON.stringify({"result":"error", "error": e}))
  } finally { //release lock

function setup() {
    var doc = SpreadsheetApp.getActiveSpreadsheet();
    SCRIPT_PROP.setProperty("key", doc.getId());

function Copy_delete() {
  var spreadsheet = SpreadsheetApp.getActive();
  spreadsheet.setActiveSheet(spreadsheet.getSheetByName('Sheet1'), true);
  spreadsheet.setActiveSheet(spreadsheet.getSheetByName('Sheet1'), true);
  var tz = spreadsheet.getSpreadsheetTimeZone();
  var sheets = spreadsheet.getSheets();
  var date = Utilities.formatDate(new Date(), tz, 'MM-dd-yyyy');
  sheets[1].setName(date);  // Rename second sheet
  var LastRow = spreadsheet.getLastRow();
  var rowString = "4:"+LastRow;
  spreadsheet.getActiveSheet().deleteRows(spreadsheet.getActiveRange().getRow(), spreadsheet.getActiveRange().getNumRows());
  //deleting the data causes reference errors in the formulas in row 3, these lines restore them
  spreadsheet.getRange('A3').setFormula('=sum(-1*A4,INDEX(A4:A, COUNT(A4:A)))*24');

function appliance_id () {
  var spreadsheet = SpreadsheetApp.getActive();
  var last = spreadsheet.getSheets().length; //index of last sheet
  var sheet = spreadsheet.getSheets()[1]; //sheet with yesterday's data that we will be analyzing
  var appliances = spreadsheet.getSheetByName("Appliances"); //sheet with appliance signatures
  var LastApp = appliances.getLastRow(); //number of appliances
  var sigRange = appliances.getRange('A2:W'+LastApp); //data range of appliance signatures
  var sigs = sigRange.getValues(); //this creates 2 dimension array of appliance signatures
  var LastRow = sheet.getLastRow(); //number of rows in yesterday's data
  var dataRange = sheet.getRange('A4:W'+LastRow); //data range of yesterday's data
  var data = dataRange.getValues(); //create 2 dimensional array of yesterday's data
  var tolerance = .3; //how close harmonic deltas must be to signature to match appliance
  for (i=0; i<LastApp-1; i++){ //loop for each appliance on appliance sheet, i will be row number on appliance sheet
    sheet.insertColumnsAfter(sheet.getLastColumn(),1); //add new column to data sheet for this appliance
    var col = sheet.getLastColumn()+1; //new column number
    sheet.getRange(1,col).setValue(sigs[i][0]); //add the appliance name to new column
    var flag = 0; //flag variable will be 0 for off and 1 for on
    var totpower = 0; //this variable will accumulate total power used by appliance
    for (j=2; j<=LastRow-4; j++){ //loop for each row of data, j will be row number on appliance sheet
      var Acurrent_delta = data[j][1]-data[j-2][1]; //A phase current change
      var Bcurrent_delta = data[j][12]-data[j-2][12]; //B phase current change
      if (flag==0 && Math.abs(Acurrent_delta-sigs[i][1])<2 && Math.abs(Bcurrent_delta-sigs[i][12])<2) { //check current change and see if it's within 2 amps of this appliances signature
        flag = 1; //if so, appliance may have turned on, so set flag to 1
        for (k=1; k<23; k++){ //after matching current, then check harmonics, k will represent column numbers for both sheets
          if (sigs[i][k]>1) { //only test the magnitude change if it's greater than 1, otherwise noise is too much
            var magdelta = data[j][k]-data[j-2][k]; //magnitude change of harmonic being tested 
            if (Math.abs(sigs[i][k]-magdelta)>tolerance*sigs[i][k]) { //tests the magnitude change, if more than tolerance from signature sets to 0. Adjust tolerance to your taste
              flag = 0;
      var time = (data[j][0]-data[j-1][0])/3600000; //calculates the time in hours from last sample
      var kwh = time*(sigs[i][1]+sigs[i][12])*120*flag/1000; //calculates the kWh of this sample
      if (flag==1 && Math.abs(Acurrent_delta+sigs[i][1])<2 && Math.abs(Bcurrent_delta+sigs[i][12])<2) { //if flag is already 1, check for negative current change to see if appliance turned off
          flag = 0;
     sheet.getRange(j+4,col).setValue(kwh); //add kWh for this sample to appropriate cell
     totpower+=kwh; //accumulate total kWh
    sheet.getRange(3,col).setValue(totpower); //add total kWh consumed by appliance at top of appropriate column
function getDailyTotal() {
  var spreadsheet = SpreadsheetApp.getActive();
  var sheet = spreadsheet.setActiveSheet(spreadsheet.getSheetByName('DailyLog'), true);
  var yesterday_data = spreadsheet.getSheets()[1];
  var LastRow = sheet.getLastRow()+1;
  var date = yesterday_data.getName();
  var Apow = yesterday_data.getRange('B3').getValue();
  var Bpow = yesterday_data.getRange('M3').getValue();
  var cost = .097; //this should be the cost/kWh for your utility company
  var days2keep = 7; //this is how many days of data you wish to keep
  //appliance totals
  //likewise add a row like this for each appliance

Photon Program

This is what the Photon runs in order to collect and process the current signature.
// This #include statement was automatically added by the Particle IDE.
#include <EmonLib.h>

#include "math.h"

double IrmsA, IrmsB, lastIrmsA, lastIrmsB, diff;
const int A=0;  //analog channel for phase A
const int B=1;  //analog channel for phase B
const int samples=1024; //number of samples to collect for FFT
const int harm=10; //number of harmonics to store
const int sampling_freq=4096; //sampling frequency
const int base_harm=20; //lowest frequency to record
const int pause=5000; //amount of time in milliseconds to pause between each sample; recommend at least 5000
int res = sampling_freq/samples; //resolution (how many Hz are represented by each index)
int step = (base_harm/res); //used to grab harmonics in for loop

float current1[samples], current2[samples], imag1[samples], imag2[samples]; //arrays for FFT
float magA[harm], magB[harm];   //array of magnitudes from most recent FFT

unsigned int period;    //sampling period
unsigned long microseconds; 

EnergyMonitor emon1;
EnergyMonitor emon2;

void setup() {
    period=round(1000000*(1.0/sampling_freq));  //calculate period based on frequency

    Particle.variable("CurrentA", IrmsA); //exposes current data to Particle cloud
    Particle.variable("CurrentB", IrmsB);

    emon1.current(A,222); //the second parameter in this function is used to calibrate to your specific current transformer/burder resistor combo. You may want to use a clamp on meter to verify your actual current draw so your power usage is accurate, otherwise you may have inaccurate results.
    emon2.current(B,97);//the second parameter in this function is used to calibrate to your specific current transformer/burden resistor combo. You may want to use a clamp on meter to verify your actual current draw so your power usage is accurate, otherwise you may have inaccurate results.

void loop() {
    //collect samples for FFT

	for (int i=0; i<samples; i++){

	    while(micros() < (microseconds+period)){

    //Run the FFT function (direction, power of 2, real array, imag array)


    //compute magnitudes
  	for (int i=1;i<=harm;i++){

    //calculate RMS current
    IrmsA = emon1.calcIrms(2000);
    IrmsB = emon2.calcIrms(2000);    

    //Convert magnitudes to strings to send to Google Sheets
    String tIrmsA = String(IrmsA,2);
    String A_1 = String(magA[0],2);
    String A_2 = String(magA[1],2);
    String A_3 = String(magA[2],2);
    String A_4 = String(magA[3],2);
    String A_5 = String(magA[4],2);
    String A_6 = String(magA[5],2);
    String A_7 = String(magA[6],2);
    String A_8 = String(magA[7],2);
    String A_9 = String(magA[8],2);
    String A_10 = String(magA[9],2);
    String tIrmsB = String(IrmsB,2);
    String B_1 = String(magB[0],2);
    String B_2 = String(magB[1],2);
    String B_3 = String(magB[2],2);
    String B_4 = String(magB[3],2);
    String B_5 = String(magB[4],2);
    String B_6 = String(magB[5],2);
    String B_7 = String(magB[6],2);
    String B_8 = String(magB[7],2);
    String B_9 = String(magB[8],2);
    String B_10 = String(magB[9],2);

    //This event publishes data to Google Sheets

    Particle.publish("GenericWebhookName","{\"IrmsA\":\"" + tIrmsA + "\",\"A1\":\"" + A_1 + "\",\"A2\":\"" + A_2 + "\",\"A3\":\"" + A_3 + "\",\"A4\":\"" + A_4 + "\",\"A5\":\"" + A_5 + "\",\"A6\":\"" + A_6 + "\",\"A7\":\"" + A_7 + "\",\"A8\":\"" + A_8 + "\",\"A9\":\"" + A_9 + "\",\"A10\":\"" + A_10 + "\",\"IrmsB\":\"" + tIrmsB + "\",\"B1\":\"" + B_1 + "\",\"B2\":\"" + B_2 + "\",\"B3\":\"" + B_3 + "\",\"B4\":\"" + B_4 + "\",\"B5\":\"" + B_5 + "\",\"B6\":\"" + B_6 + "\",\"B7\":\"" + B_7 + "\",\"B8\":\"" + B_8 + "\",\"B9\":\"" + B_9 + "\",\"B10\":\"" + B_10 + "\"}",5,PRIVATE);

//FFT function from http://paulbourke.net/miscellaneous/dft/
short FFT(short int dir, int m, float *rx, float *iy) {
	int n, i, i1, j, k, i2, l, l1, l2;
	float c1, c2, tx, ty, t1, t2, u1, u2, z;

	/* Calculate the number of points */
	n = 1;
	for (i=0;i<m;i++) 
		n *= 2;

	/* Do the bit reversal */
	i2 = n >> 1;
	j = 0;
	for (i=0;i<n-1;i++) {
		if (i < j) {
			tx = rx[i];
			ty = iy[i];
			rx[i] = rx[j];
			iy[i] = iy[j];
			rx[j] = tx;
			iy[j] = ty;
		k = i2;
		while (k <= j) {
			j -= k;
			k >>= 1;
		j += k;

	/* Compute the FFT */
	c1 = -1.0; 
	c2 = 0.0;
	l2 = 1;
	for (l=0;l<m;l++) {
		l1 = l2;
		l2 <<= 1;
		u1 = 1.0; 
		u2 = 0.0;
		for (j=0;j<l1;j++) {
			for (i=j;i<n;i+=l2) {
				i1 = i + l1;
				t1 = u1 * rx[i1] - u2 * iy[i1];
				t2 = u1 * iy[i1] + u2 * rx[i1];
				rx[i1] = rx[i] - t1; 
				iy[i1] = iy[i] - t2;
				rx[i] += t1;
				iy[i] += t2;
			z =  u1 * c1 - u2 * c2;
			u2 = u1 * c2 + u2 * c1;
			u1 = z;
		c2 = sqrt((1.0 - c1) / 2.0);
		if (dir == 1) 
			c2 = -c2;
		c1 = sqrt((1.0 + c1) / 2.0);

	/* Scaling for forward transform */
	if (dir == 1) {
		for (i=0;i<n;i++) {
			rx[i] /= n;
			iy[i] /= n;





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Keith Snyder

Keith Snyder

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