Temperature

TMP36 Temperature Sensor

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 pins, 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° C = 750 mV, 0° C = 500mV). To convert this from the digital value to degrees, we will use some of the Arduino's math abilities. We'll output the value to the console. Let's get to it.

The TMP36 Datasheet: http://ardx.org/TMP36

Parts

  • 2 pin header x 4
  • TMP36 Temperature sensor
  • jumper wires

Circuit Layout

Circuit Layout

Circuit Assembly

Assembly Diagram

Assembly video: http://ardx.org/VIDE10

Code

You can find this code in code/CIRC-10-code-temperaturesensor.js

var five = require("johnny-five");
var board = new five.Board();

board.on("ready", function() {
  var temp = new five.Temperature({
    pin: "A0",
    controller: "TMP36"
  });

  temp.on("change", function() {
    console.log("Temp: %d", this.celsius);
  });
});

Troubleshooting

Nothing Seems to Happen

This program has no outward indication it is working. To see the results you must look at the console output.

Temperature Value is Unchanging

Try pinching the sensor with your fingers to heat it up or pressing a bag of ice against it to cool it down.

Extending the Code

Outputting voltage:

This is a simple matter of changing one line. Our sensor outputs 10mv per degree centigrade so to get voltage we display the value from the sensor. Change the line console.log("temp is " + cel); to print value instead of cel

Outputting degrees Fahrenheit:

Again this is a simple change requiring only math. To convert degrees C to degrees F we use the formula:

F = C * 1.8) + 32

Add the line:

var fahrenheit = (cel * 1.8) + 32;

More

For more details on this circuit, see http://ardx.org/CIRC010