Home Monitoring (home made) – Temperature

Reading the temperature of the hot water tank

This one is not as easy as the export meter as the meter cupboard and the hot water tank are not in the same area as one another, so we had to purchase another Arduino. This time instead of a wifi shield I got the Ethernet shield – in reflection, not too wise a choice as the cat6 (yes overkill) cable that runs to the cupboard took a collective 5 hours to install.

For the temperature sensor we bought a linear thermistor (for those interested in replicating this, you can use one of these: http://cpc.farnell.com/microchip/mcp9700a-e-to/thermistor-linear-10mv-c-to-92/dp/SC10459)

The temperature sensor is then pushed in through the insulating hot water tank jacket with a dob of conducting gel to help the sensor get as good a reading as possible.

(The program loaded on the Arduino is in the next part)

Next Part

Part 4: Reading when the hot water is heated by solar from the Wattson

Home Monitoring (home made) – Export

Reading the export meter

Reading the export meter is relatively easy as the Arduino in the meter cupboard can be extended to have another light voltage converter to read the export meter.

So we purchased another part from CPC (for those interested in replicating this, you can use one of these: http://cpc.farnell.com/taos/tsl257-lf/sensor-light-voltage-converter/dp/SC12392?Ntt=SC12392)

The Arduino program then needed extending to attach another interrupt for the export meter. The only gotcha here is that the export meter flashes 1000 times for 1kh, but the import meter only 800 times for 1kwh.

And it looks like this:


The complete Arduino program:

#include <SPI.h>
#include <WiFi.h>
#include <WiFiUDP.h>

///////// CHANGEABLE VALUES /////////

double importMultiplier = 1.25;
double exportMultiplier = 1.0;

char ssid[] = "REPLACE THIS";
char pass[] = "REPLACE THIS";

char pompeii[] = "";
int pompeiiPort = 80;

double minutesBetweenCalls = 1.0;

///////// CHANGEABLE VALUES ABOVE /////////

int status = WL_IDLE_STATUS;

WiFiClient pompeiiClient;
char pompeiiService[] = "/pvoutput-post.php";

unsigned long importImpulseCount = 0;
unsigned long exportImpulseCount = 0;

unsigned long lastTimeUploaded = millis();

boolean importInterruptAttached = false;
boolean exportInterruptAttached = false;

double millisecondsPerMinute = 60000.0;
double timeBetweenCalls = minutesBetweenCalls * millisecondsPerMinute;

void setup() {

void connectToWiFi()
  // attempt to connect to Wifi network:
  while ( status != WL_CONNECTED) {
    Serial.print("Attempting to connect to WPA SSID: ");
    // Connect to WPA/WPA2 network:    
    status = WiFi.begin(ssid, pass);


  Serial.print("Connected to the network");

void loop() {

  if (isTimeToUploadData())
    Serial.println("Uploading data");

void addImportFlashInterrupt()
  if (!importInterruptAttached)
    importInterruptAttached = true;
    Serial.println("Attaching import interrupt on pin 3");
    attachInterrupt(1, flashImport, FALLING);

void addExportFlashInterrupt()
  if (!exportInterruptAttached)
    exportInterruptAttached = true;
    Serial.println("Attaching export interrupt on pin 2");
    attachInterrupt(0, flashExport, FALLING);

boolean isTimeToUploadData() {
  unsigned long time = millis();

  if( (time - lastTimeUploaded) >= timeBetweenCalls) {
    Serial.println("Time to upload");
    lastTimeUploaded = time;
    return true;
  return false;

void printWifiData() {
  // print your WiFi shield's IP address:
  IPAddress ip = WiFi.localIP();
  Serial.print("IP Address: ");

/* Handles the interrupt flash logic */
void flashImport() {

void flashExport() {

void sendResultsToPompeii() {

  String postData = getPostData();

  if (pompeiiClient.connect(pompeii, pompeiiPort)) {
    Serial.println("connected to pompeii");
    // Make a HTTP request:
    pompeiiClient.print("POST ");
    pompeiiClient.println(" HTTP/1.1");
    pompeiiClient.print("Host: ");
    pompeiiClient.println("Accept: text/html");
    pompeiiClient.println("Content-Type: application/x-www-form-urlencoded; charset=UTF-8");
    pompeiiClient.print("Content-Length: ");
    pompeiiClient.println("Pragma: no-cache");
    pompeiiClient.println("Cache-Control: no-cache");
    pompeiiClient.println("Connection: close");


    Serial.println("Called pompeii");

String calculateImportWattsAndResetFlashes()
  if (importImpulseCount == 0UL) {
    return "0";

  double watts = (importImpulseCount * importMultiplier);
  Serial.print("Calculated Import Watts: ");
  importImpulseCount = 0UL;
  return doubleToString(watts);

String calculateExportWattsAndResetFlashes()
  if (exportImpulseCount == 0UL) {
    return "0";

  double watts = (exportImpulseCount * exportMultiplier);
  Serial.print("Calculated Export Watts: ");
  exportImpulseCount = 0UL;
  return doubleToString(watts);

String doubleToString(double valueToConvert)
  char doubleChar[15];
  String dts = String(doubleChar);
  return dts;

String getPostData()
  String importWatts = calculateImportWattsAndResetFlashes();
  String exportWatts = calculateExportWattsAndResetFlashes();
  String wattHourPeriod = doubleToString(timeBetweenCalls);
  return "iw=" + importWatts + "&ew=" + exportWatts + "&msBetweenCalls=" + wattHourPeriod;

Next Part

Part 3: Reading the temperature of the hot water tank

Home Monitoring (home made) – Overview

We have been working towards monitoring more and more items within the house to see the benefits of the solar array. Last time I posted an article about the meter reader which uses an Arduino and a light voltage converter to read the impulses from the import meter (a huge thanks goes out to Lars for his post here: http://www.lindnilsson.dk/lars/en/powermeter.php) but we wanted to expand on that and add in:

(Because of the size of the code, this article has been split in to separate pages)

And finally the results of all work!