Monday, 19 August 2013

Digital Thermometer

This tutorial shows an interesting way to read the temperature from the environment with the Arduino, and shows it on a LCD 16x2 display (in Fahrenheit), by using some elements from its programming and the temperature LM35DZ sensor.
For that, it will be necessary the following components:
- 1 Arduino board
- 1 LCD 16x2 display
- 1 10K potentiometer
- 1 Temperature LM35 sensor
- Jumpers for connection
This sensor captures the external temperature and converts it into a corresponding voltage value. In this circuit, we connect the output Vo of the sensor to the Arduino’s A0 pin, which converts it to a float value of temperature, and then, exhibits it on the LCD. The 10K potentiometer adjusts the contrast of the display.

Now, set up the circuit below with the Arduino and the other components:  
And then, open the Arduino’s IDE and enter the following code:

#include  <LiquidCrystal.h>         // Include the library to use a LCD display
#define          sensor           0        // Define the A0 pin as “sensor”

int  Vin;           //  Variable to read the value from the Arduino’s pin
float  Temperature; //  Variable that receives the converted voltage value to temperature
float     TF;   // Variable to receive the converted value from  ºC to ºF

LiquidCrystal  lcd    (12, 11, 5, 4, 3, 2); 
/* The function above declares which Arduino’s pins will be used for controlling the LCD */
void  setup()
  lcd.begin(16, 2);                            //  It tells the Arduino that the display is a 16x2 type
  lcd.print("Temperature: ");           //  Send the text to the screen of the display.
void  loop()
  Vin = analogRead (sensor);  /*   Tells the Arduino to read the pin and stores the value in “Vin” */
  Temperature=(500*Vin)/1023;  /* Converts the voltage value into temperature and stores it into the “Temperature”  variable  (in  ºC)*/
TF = ((9*Temperature)/5)+32; // Converts  ºC to ºF
  lcd.setCursor(0, 1);           // Moves  the cursor of the display to the next line
  lcd.print(TF);    // Exhibits the value of the temperature on the display
  lcd.print(" F");         // Writes “F” to indicate that it is in Fahrenheit scale.

  delay(1000);  //  Waits for a second to read the pin again
In the end, upload the code to your Aduino.
Your project to show the temperature is ready!!! We hope you have enjoyed. Any doubts, post here.
Note: The LM35DZ sensor converts temperature values from -55ºC to 150ºC.
If somebody is interested, this is the explanation for the conversion calculation from voltage to temperature done by the software.
In this sensor, for each 1ºC received, the Vo output is added in 10mV, in a range from 0 to 5V, with 10 bits of resolution for Analog/Digital conversion (1024 different values to represent the temperature).
Thus, the maximum value (1023, therefore it is from 0 to 1023) will be 5V. The half will match 511 or 2.5V, and so forth. For calculation purposes, there would be 5V in the output of the sensor for a temaprature value of 500ºC (which is different in a real situation). However, this regard lets us generalize it to the following relation:
Temperature  ----- Vin
         500ºC  ----- 1023              (maximum values)

So, there will be:
Temperature = (500*Vin)/1023, but as it is in ºC and we want in ºF, we convert it:
TF = ((9*Temperature)/5)+32, and this is the printed value on the LCD display.

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