Sunday, 9 February 2014

Building Love-O-Meter by using a temperature sensor

This "Love-O-Meter" is based on the tutorial by Arduino and it comes with the starter kit. It uses a temperature sensor to measure the warmth of your skin and then starts to turn on (or off) the LEDs  indicated by the temperature.

The components
  • Arduino UNO
  • Breadboard
  • Jumper wires
  • LEDs
  • 220 ohm resistors
  • TMP36 temperature sensor

Building the Circuit

At first I ran the "Hello World" for Arduino to make sure the environment would work as expected. Now I could start to connect the jumper wires between Arduino UNO and the breadboard.

As usually I connected the breadboard to power (5V) and to the ground (GND). I inserted the TMP36 on the breadboard so the rounded part of the sensor would face away from Arduino.

I attached 3 LED lights and the resistors and connected them with Arduino. The lights should react to the heat of the finger and if the temperature would get hot enough all the lights would be on and would also tell you if you are a hot lover or not...

The circuit

The result and the code

Everything worked like a charm and my love-o-meter was ready for action. The components worked fine together and I was happy with the result. When I held my finger on the sensor the blue LED turned on and after a while the yellow started to shine too.

  Arduino Starter Kit example
 Project 3  - Love-O-Meter
 This sketch is written to accompany Project 3 in the
 Arduino Starter Kit
 Parts required:
 1 TMP36 temperature sensor 
 3 red LEDs
 3 220 ohm resistors
 Created 13 September 2012
 by Scott Fitzgerald
 This example code is part of the public domain 

// named constant for the pin the sensor is connected to
const int sensorPin = A0;
// room temperature in Celcius
const float baselineTemp = 20.0;

void setup(){
  // open a serial connection to display values
  // set the LED pins as outputs
  // the for() loop saves some extra coding
  for(int pinNumber = 2; pinNumber<5; pinNumber++){
    digitalWrite(pinNumber, LOW);

void loop(){
  // read the value on AnalogIn pin 0 
  // and store it in a variable
  int sensorVal = analogRead(sensorPin);

  // send the 10-bit sensor value out the serial port
  Serial.print("sensor Value: ");

  // convert the ADC reading to voltage
  float voltage = (sensorVal/1024.0) * 5.0;

  // Send the voltage level out the Serial port
  Serial.print(", Volts: ");

  // convert the voltage to temperature in degrees C
  // the sensor changes 10 mV per degree
  // the datasheet says there's a 500 mV offset
  // ((volatge - 500mV) times 100)
  Serial.print(", degrees C: "); 
  float temperature = (voltage - .5) * 100;

  // if the current temperature is lower than the baseline
  // turn off all LEDs
  if(temperature < baselineTemp){
    digitalWrite(2, LOW);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
  } // if the temperature rises 2-4 degrees, turn an LED on 
  else if(temperature >= baselineTemp+2 && temperature < baselineTemp+4){
    digitalWrite(2, HIGH);
    digitalWrite(3, LOW);
    digitalWrite(4, LOW);
  } // if the temperature rises 4-6 degrees, turn a second LED on  
  else if(temperature >= baselineTemp+4 && temperature < baselineTemp+6){
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, LOW);
  } // if the temperature rises more than 6 degrees, turn all LEDs on
  else if(temperature >= baselineTemp+6){
    digitalWrite(2, HIGH);
    digitalWrite(3, HIGH);
    digitalWrite(4, HIGH);

Sources , Arduino Projects Book
Based on the prototype course by Tero Karvinen ( the book - Karvinen 2011: Make Arduino Bots and Gadgets 

Sunday, 2 February 2014

Using a button to control the LED light

This time my project was to configure how to build a button that would turn on and off depending if the user is pushing it or not. While holding the button down the LED should stay on until removing the finger.

For this assignment I used the fallowing components:

  • Arduino UNO and USB
  • Jumper wires
  • LED light
  • Breadboard
  • Button
  • 10k ohm resistor

At first I run the "Hello World" for Arduino and made sure that the LED I was using worked properly (read my previous post).

I attached the button in the middle of the breadboard so the legs were touching the both "sides" of it.

Now I started to connect the jumper wires between the Arduino UNO and the breadboard. In order to get it working like in the sample code (Ardoino > Examples > 02.Digital > Button)
I linked the wires with Arduino's 5V (red wire, positive) and ground (black wire, negative) to the equal holes on the very corner of the breadboard (+ and -). I put the white jumper wire to connect the positive circuit to the button and used 10k ohm resister between the same line with grounds wire (violet) and the other leg of the button.

Finally I connected the LED to digital pin 2 and attached the push button with the green wire to Ardoino's pin 2. I ran the code and tested my device successfully. While pressing the button down I was able to keep the light on but when I took my finger away the light turned off immediately.

Sources -
Based on the prototype course by Tero Karvinen (
and the book - Karvinen 2011: Make Arduino Bots and Gadgets