Hooking up a Peltier Device with the IOIO

For this demo I used as a reference the how to use a peltier with arduino demo from GarageLab
and the simple analog output demo from Mitch Tech.
images are CC BY-NC-SA 3.0
The Peltier is a Thermoelectric device. Which means that if you pass a current through it, it will generate a temperature differential. Basically one side will get HOT and the other will get COLD.

With this demo you will learn how to hook it up to your IOIO board and control the temperature.

You will also need to use an external power supply because the peltier will want to draw more current than what the IOIO can safely supply.


  • Peltier
  • IOIO OTG Board
  • an Android device
  • USB or BT connection to your Android device
  • Power source for the IOIO
  • Power source for the Peltier
  • N-channel Mosfet
  • 10K resistor
  • circuit cables



First you must build your circuit.
Breadboard Drawing

This is not a complicated circuit. I used a IRF3710 N-channel MOSFET which connects the Source to Ground, the Drain to one wire of the Peltier and the Gate to pin 34 of the ioio.

Make sure you know which pins on your MOSFET are which or your circuit will not work and you will have no idea why. It doesn't matter which wire of the peltier is positive or negative, this will just change which side gets hot and which side get cold.

Lastly, make sure that both grounds of your power sources are connected, this is always good practice.


The code is a simple Hello IOIO with a scrollbar to control the temperature of the Peltier. We control the temperature by using a PWM pin (I used 34) to turn the MOSFET on and off.

public class GlassHeatMain extends IOIOActivity 
                           implements OnSeekBarChangeListener{

 private static final String TAG = "HeatGlassMain";

 //Peltier controls
 private final int mOutHeatPin = 34;    //This pin can serve as PWM output
 private final int mPWMFreq = 100;      //The frequency of the PWM signal
 private final int POLLING_DELAY = 150; //Wait this lont to update the signal
 private final int MULTIPLIER = 100;

 //HeatBar UI
 private SeekBar mHeatBar;	
 private int mHeatValue;
 private TextView mHeatText;
 private long mLastChange;

This first part is the basic setup. Start a pin (34 in this case) to be a PWM output and the variables that we will be using.
We also set up a scrollbar to control the PWM output.

 public void onCreate(Bundle savedInstanceState) {

  mHeatText = (TextView) findViewById(R.id.seekBarText);
  mHeatBar = (SeekBar) findViewById(R.id.seekBarHeat);


Again, basic UI setup.

  protected void onStart() {
 protected void onStop() {

These methods control the Activity Lifecycle

 class Looper extends BaseIOIOLooper {
  private PwmOutput mHeatPWM;

  protected void setup() throws ConnectionLostException {
   mHeatPWM = ioio_.openPwmOutput(mOutHeatPin, mPWMFreq);

Here we actually tell the IOIO board to set the pint as PWM output.

  public void loop() throws ConnectionLostException {
   try {
    mHeatValue = mHeatBar.getProgress();
    Log.i(TAG, "setPulseWidth: "+ mHeatValue*MULTIPLIER);
    } catch (InterruptedException e) {

In the loop we constantly check for the value of the ScrollBar and send that value to the pin to control the Peltier.
The ScrollBar value is multiplied by the MULTIPLIER. I found that I had to do this so that the heat on the Peltier was actually noticeable within the values of the ScrollBar
Finally the thread sleeps for 100 milliseconds before looping again.

 protected IOIOLooper createIOIOLooper() {
  return new Looper();

 public void onStartTrackingTouch(SeekBar seekBar) {
  mLastChange = System.currentTimeMillis();

Set the initial value of the MLastChange variable to the current time.

 public void onProgressChanged(SeekBar seekBar, int prog, boolean fromUser) {
  if (System.currentTimeMillis() - mLastChange > POLLING_DELAY) {
   mLastChange = System.currentTimeMillis();

Compare the time elapsed since last check with the POLLING_DELAY variable. If the elapsed time is more than the POLLING_DELAY then reset then go to the handleHeat() method and reset the mLastChange variable for the next comparison.

 public void onStopTrackingTouch(SeekBar seekBar) {

Also go to the handleHeat() method if the user has stopped touching the ScrollBar.

 private void handleHeat(final SeekBar seekBar){
  mHeatValue = seekBar.getProgress();
  mHeatText.setText("Heat Value: " + mHeatValue*MULTIPLIER);

The method that updates the mHeatValue variable with the value on the ScrollBar and also updates the text on the UI.