House Temperature Monitor

Recently a family member had his furnace fail while he was away from his house for a long period of time in the winter. His pipes burst and caused quite the mess. This project describes a temperature sensor that broadcasts the temperature in his house to the pachube data logging website. This allows him to check on his house from anywhere he has internet access.

What is it?

This project includes a temperature sensor and a small computer that can send the temperature readings from inside your house to the internet. This will allow you to monitor the temperature in your house and detect if there may be a problem from anywhere that you have internet access.


  1. Plug the wall wart into an 120V electrical outlet
  2. Plug the cat5 ethernet cord into the back of your router as if it was a computer
  3. For now, disregard the extra USB cable
  4. Wait 10 minutes
  5. Log onto to see the temperature inside your house

How it Works

The temperature sensor (Analog Devices TMP36, source) is a small diode on an integrated circuit that outputs a voltage proportional to the temperature between -50 and 125 degrees Celsius. A small microcontroller (Arduino, lowest circuit board in the stack) reads the voltage output by the sensor. The voltage reading is converted to degrees Fahrenheit by the computer code running in the Arduino. Finally the ethernet shield (source, upper circuit board in the stack) sends the temperature in Fahrenheit to a website named pachube. The pachube website logs the data sent by the ethernet shield and presents the information in an easy to read plot. The procedure from raw temperature measurement to submission to pachube is repeated every five minutes.

Some things to note

  1. The Arduino uses very little power, so I would suggest leaving it pluged in all the time. After a few weeks of being without power the Arduino will “forget” the code that was installed on it.
  2. If the Arduino forgets its programing, the USB cord can be used to upload code to the board.
  3. Pachube is a free website. Therefore we have to tolerate the fact that it has an uptime of about 90%. Since I have been using the site over the past few months on a rare occasion I have seen the site go down for as long as six hours. In most cases service interruptions last less than 15 minutes.
  4. If for whatever reason the wires to the temperature sensor become detached, you can reconnect them to the holes labeled:
    1. Yellow → A0
    2. Blue → 3.3V
    3. White → GND
    4. If you hook them up backwards the sensor will get really hot and possibly catch on fire.
  5. The ethernet cord has a tendency to come loose. If the system is not working as expected try pushing the cat5 plug firmly into its connector.


To determine if you arduino/ethernet shield are operating correctly reference the status lights:

Status lights for a properly operating board. The left most light is the power light (green). The status light at the lower right below the cat5 connector is the internet connection link button (yellow). The light at the upper right above the cat5 connector is the network connection light (green). When the board is transmitting data the yellow "Rx" light will flash rapidly.

Completed Project Picture

Tupperware enclosure for the arduino/ethernet shield. Two small computer screws secure the arduino to the base of the tupperware.

Tie off on the side of the tupperware to prevent the power and cat5 cables from pulling loose from the circuit boards. The temperature sensor is above the lid of the tupperware.

Arduino Source Code

modified by ryan y11m12d28
Requires account at
Pachube login/pass: YOUR ID / LOGIN
Pin Connections
Arduino : Temperature Sensor
A0: signal
3.3V: Vin
GND : Ground  
 Pachube sensor client
 This sketch connects an analog sensor to Pachube (
 using a Wiznet Ethernet shield. You can use the Arduino Ethernet shield, or
 the Adafruit Ethernet shield, either one will work, as long as it's got
 a Wiznet Ethernet module on board.
 * Analog sensor attached to analog in 0
 * Ethernet shield attached to pins 10, 11, 12, 13
 created 15 March 2010
 updated 4 Sep 2010
 by Tom Igoe
 This code is in the public domain.
#include <SPI.h>
#include <Ethernet.h>
// assign a MAC address for the ethernet controller.
// fill in your address here:
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};
// assign an IP address for the controller:
byte ip[] = { 192,168,1,199};
//byte gateway[] = { 192,168,1,1}; 
//byte subnet[] = { 255, 255, 255, 0 };
// The address of the server you want to connect to (
//byte server[] = { 209,40,205,190 }; 
byte server[] = { 173,203,98,29 }; 
// initialize the library instance:
Client client(server, 80);
long lastConnectionTime = 120001; // last time you connected to the server, in milliseconds
boolean lastConnected = false; // state of the connection last time through the main loop
const long postingInterval = 120000; //delay between updates to
unsigned long t = 0;

void setup() {
 // start the ethernet connection and serial port:
 Ethernet.begin(mac, ip);
 // give the ethernet module time to boot up:
void loop() {
 // read the analog sensor:
 //int sensorReading = analogRead(A0); 
 float currentTemp = getTemp();
 int sensorReading = (int) currentTemp; 
 //Serial.print("Analog Sensor Reading: ");
// if there's incoming data from the net connection.
 // send it out the serial port. This is for debugging
 // purposes only:
 if (client.available()) {
 char c =;
// if there's no net connection, but there was one last time
 // through the loop, then stop the client:
 if (!client.connected() && lastConnected) {
// if you're not connected, and ten seconds have passed since
 // your last connection, then connect again and send data:
 if(!client.connected() && (millis() - lastConnectionTime > postingInterval)) {
 // store the state of the connection for next time through
 // the loop:
 lastConnected = client.connected();
// this method makes a HTTP connection to the server:
void sendData(int thisData) {
 // if there's a successful connection:
 if (client.connect()) {
 Serial.print("Analog Sensor Reading: ");
 float t = millis(); // miliseconds
 t = t/1000.0; // seconds
 t = t/60.0; //minutes
 Serial.print("Time Stamp: ");
 Serial.println(" minutes");
 // send the HTTP PUT request. 
 // fill in your feed address here:
 client.print("PUT /api/YOUR_FEED_NUMBER_GOES_HERE.csv HTTP/1.1\n");
 // fill in your Pachube API key here:
 client.print("X-PachubeApiKey: YOUR_PACHUBE_API_KEY_GOES_HERE\n");
 client.print("Content-Length: ");
// calculate the length of the sensor reading in bytes:
 int thisLength = getLength(thisData);
 client.println(thisLength, DEC);
// last pieces of the HTTP PUT request:
 client.print("Content-Type: text/csv\n");
 client.println("Connection: close\n");
// here's the actual content of the PUT request:
 client.println(thisData, DEC);
// note the time that the connection was made:
 lastConnectionTime = millis();
 else {
 // if you couldn't make a connection:
 Serial.println("connection failed");

// This method calculates the number of digits in the
// sensor reading. Since each digit of the ASCII decimal
// representation is a byte, the number of digits equals
// the number of bytes:
int getLength(int someValue) {
 // there's at least one byte:
 int digits = 1;
 // continually divide the value by ten, 
 // adding one to the digit count for each
 // time you divide, until you're at 0:
 int dividend = someValue /10;
 while (dividend > 0) {
 dividend = dividend /10;
 // return the number of digits:
 return digits;

float getTemp(){
 //getting the voltage reading from the temperature sensor
 int reading = analogRead(A0); 
 // convert reading into volts, then mV
 float voltage = (reading * 5)/1024.0;
 voltage = voltage*1000.0;
 //converting from 10 mv per degree wit 500 mV offset
 float temperatureC = (voltage - 500) / 10 ; 
 // now convert to Fahrenheight
 float temperatureF = (temperatureC * 9.0 / 5.0) + 32.0;
 return temperatureF;

About Ryan

Ryan is currently a National Research Council Postdoctoral Research Fellow at the Air Force Research Laboratory. His research area includes Prognostic Health Management of Electronics. For more information please visit:
This entry was posted in Project and tagged , , , , . Bookmark the permalink.

2 Responses to House Temperature Monitor

  1. Pingback: Monitor household temperature over the Internet with Arduino « freetronicsblog

  2. Pingback: House Temperature Monitor using Arduino -Arduino for Projects

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s