CIRC
10

What We´re Doing

What´s the next phenomena we will measure with our Arduino? Temperature. To do this we'll use a rather complicated IC (integrated circuit) hidden in a package identical to our P2N2222AG transistors. It has three pin's, ground, signal and +5 volts, and is easy to use. It outputs 10 millivolts per degree centigrade on the signal pin (to allow measuring temperatures below freezing there is a 500 mV offset eg. 25 degrees C = 750 mV, 0 degrees C = 500mV). To convert this from the digital value to degrees, we will use some of the Arduino's math abilities. Then to display it we'll use one of the IDE's rather powerful features, the debug window. We'll output the value over a serial connection to display on the screen. Let's get to it.

One extra note, this circuit uses the Arduino IDE's serial monitor. To open this, first upload the program then click the button which looks like a square with an antennae.

The Circuit

The Parts

CIRC-10 Breadboard Sheet x1

2 Pin Header x4

TMP36 Temperature Sensor x1

Wire

Code (no need to type everything in just)

Download the Code from ( http://ardx.org/CODE10 )
(and then copy the text and paste it into an empty Arduino Sketch)

/*     ---------------------------------------------------------
 *     |  Arduino Experimentation Kit Example Code             |
 *     |  CIRC-10 .: Temperature :. (TMP36 Temperature Sensor) |
 *     ---------------------------------------------------------
 *
 * A simple program to output the current temperature to the IDE's debug window
 *
 * For more details on this circuit:
 * https://learn.adafruit.com/tmp36-temperature-sensor/using-a-temp-sensor
 */

//TMP36 Pin Variables
int temperaturePin = 0; //the analog pin the TMP36's Vout (sense) pin is connected to
                        //the resolution is 10 mV / degree centigrade
                        //(500 mV offset) to make negative temperatures an option

/*
 * setup() - this function runs once when you turn your Arduino on
 * We initialize the serial connection with the computer
 */
void setup()
{
  Serial.begin(9600);  //Start the serial connection with the copmuter
                       //to view the result open the serial monitor
                       //last button beneath the file bar (looks like a box with an antenae)
}

void loop()                     // run over and over again
{
 float temperature = getVoltage(temperaturePin);  //getting the voltage reading from the temperature sensor
 temperature = (temperature - .5) * 100;          //converting from 10 mv per degree with 500 mV offset
                                                  //to degrees ((voltage - 500mV) times 100)
 Serial.println(temperature);                     //printing the result
 delay(1000);                                     //waiting a second
}

/*
 * getVoltage() - returns the voltage on the analog input defined by pin
 */
float getVoltage(int pin){
 return (analogRead(pin) * .004882814); //converting from a 0 to 1023 digital range
                                        // to 0 to 5 volts (each 1 reading equals ~ 5 millivolts)
}

Not Working? 3 things to try

Making it Better?

Outputting voltage:

This is a simple matter of changing one line. Our sensor outputs 10mv per degree centigrade so to get voltage we simply display the result of getVoltage().

delete the line temperature = (temperature - .5) * 100;

Outputting degrees Fahrenheit:

Again this is a simple change requiring only math. To go from degrees C ----> degrees F we use the formula ( F = C * 1.8) + 32 ). Add the line

  temperature = (((temperature - .5) * 100)*1.8) + 32;

before Serial.println(temperature);

More informative output:

Lets add a message to the serial output to make what is appearing in the Serial Monitor more informative. To do this first revert to the original code then change:
  Serial.println(temperature); ---->

  Serial.print(temperature);
  Serial.println(" degrees centigrade");

The change to the first line means when we next output it will appear on the same line, then we add the informative text and a new line.

Changing the serial speed:

If you ever wish to output a lot of data over the serial line, time is of the essence. We are currently transmitting at 9600 baud but much faster speeds are possible. To change this, change the line:
  Serial.begin(9600); ----> Serial.begin(115200);
Upload the sketch, turn on the serial monitor, then change the speed from 9600 baud to 115200 baud in the pull down menu. You are now transmitting data 12 times faster.