Lab: Mouse Control With Joystick

Last edited 26 August 2014 by Benedetta Piantella

Introduction

In this lab, you’ll build an alternative computer mouse using an Arduino Leonardo using a joystick to move the mouse left, right, up and down. You’ll use the joystick’s select button to replace the mouse button as well. You’ll see how to scale the analog outputs of the joystick to a reasonable range using the map() function.

A joystick is typically made up of two potentiometers, one for the X axis and one for the Y axis. The potentiometers are mounted so that when the joystick is at rest in the center, the potentiometers are at the middle of their range. Some joysticks like the Thumb Joystsick used here also have a pushbutton that you can press by pushing down on the stick. (Note: SparkFun and Parallax have equivalent models as well.)

What You’ll Need to Know

To get the most out of this lab, you should be familiar with the following concepts. You can check how to do so in the links below:

Things You’ll Need

For this lab you will need the following parts:
Solderless breadboard Hook-up wire Arduino
Solderless Breadboard 22-AWG hook-up wire Arduino Leonardo
Resistors Switch Joystick
10kilohm resistors Switch or pushbutton Thumb Joystsick

Click on any image for a larger view

Prepare the breadboard

Connect power and ground on the breadboard to power and ground from the microcontroller. On the Arduino module, use the 5V and any of the ground connections:

Made with Fritzing

Add a pushbutton

Attach a pushbutton to digital pin 2. Connect one side of the pushbutton to 5 volts, and the other side of the pushbutton to a 10-kilohm resistor. Connect the other end of the resistor to ground. Connect the junction where the pushbutton and the resistor meet to digital pin 2. (For more on this digital input circuit,see the Digital Input Lab)

Add a thumb joystick

Add a thumb joystick, attaching the Xout to analog input 0, the Yout to analog input 1, and the select button to digital input 3.

Program the module to read the pushbutton

Follow the same steps as you did in the first Mouse Control lab to read when the pushbutton on pin 2 is pressed. Your code should only print out a message when the button changes state. Similarly, set up a global variable to track whether or not you’re controlling the mouse, called mouseIsActive. Each time the pushbutton on pin 2 is pressed, change the state of this variable from false to true, just like you did in the first mouse control lab.

// Global variables:
int lastButtonState = LOW;            // state of the button last time you checked
boolean mouseIsActive = false;    // whether or not the Arduino is controlling the mouse

void setup() {
  // initialize serial communication:
  Serial.begin(9600);
  pinMode(2, INPUT);
}

void loop() {
  // read the first pushbutton:
  int buttonState = digitalRead(2);

  // if it's changed and it's high, toggle the mouse state:
  if (buttonState != lastButtonState) {
    if (buttonState == HIGH) {
      // if mouseIsActive is true, make it false;
      // if it's false, make it true:
      mouseIsActive = !mouseIsActive;
      Serial.print("Mouse control state: ");
      Serial.println(mouseIsActive);
    }
  }
  // save button state for next comparison:
  lastButtonState = buttonState;
}

Program the Leonardo to read the Joystick

Add code to the main loop to read the joystick X and Y outputs and print them.

// Global variables:
int lastButtonState = LOW;            // state of the button last time you checked
boolean mouseIsActive = false;    // whether or not the Arduino is controlling the mouse

void setup() {
  // initialize serial communication:
  Serial.begin(9600);
  pinMode(2, INPUT);
}

void loop() {
  // read the first pushbutton:
  int buttonState = digitalRead(2);

  // if it's changed and it's high, toggle the mouse state:
  if (buttonState != lastButtonState) {
    if (buttonState == HIGH) {
      // if mouseIsActive is true, make it false;
      // if it's false, make it true:
      mouseIsActive = !mouseIsActive;
      Serial.print("Mouse control state: ");
      Serial.println(mouseIsActive);
    }
  }
  // save button state for next comparison:
  lastButtonState = buttonState;

  // read the analog sensors:
  int sensor1 = analogRead(A0);
  delay(1);
  int sensor2 = analogRead(A1);
  // print their values. Remove this when you have things working:
  Serial.print(sensor1);
  Serial.print("  ");
  Serial.println(sensor2); 
}

Map the X and Y output readings

The Mouse.move() command has three parameters: the horizontal movement, the vertical movement, and the scroll wheel movement. All movements are relative, so Mouse.move(1,0,0); moves one pixel to the right; Mouse.move(-1,0,0); moves one pixel to the left; Mouse.move(0,1,0); moves one pixel down; and Mouse.move(0,-1,0); moves one pixel up. Moving the mouse more than about 5 pixels in any direction is a very fast move. So the ideal range for the joystick is if it can move the cursor 5 pixels in any direction.

In order to do this, you need to scale the X and Y outputs from the default range that they return (0 to 1023) to a range from -5 to 5. You can do this using the map() function. Map takes five parameters: the input value, the range of the input value, and the desired output range, like so:

result = map(inputValue, inputMinimum, inputMaximum, outputMinimum, outputMaximum);

So, if your input range is 0 to 1023, and your output range is -5 to 5, you might map like this:

result = map(sensorReading, 0, 1023, -5, 5);

Add code to the main loop to map the X and Y outputs to a range from -5 to 5. Print the mapped values instead of the original sensor values.

// read the analog sensors:
  int sensor1 = analogRead(A0);
  delay(1);
  int sensor2 = analogRead(A1);

  int xAxis = map(sensor1, 0, 1023, -5, 5);
  int yAxis = map(sensor2, 0, 1023, -5, 5);

 // print their values. Remove this when you have things working:
  Serial.print(xAxis);
  Serial.print("  ");
  Serial.println(yAxis);

NOTE: If your joystick defaults to -1 at rest on one axis or both, try adding 1 to the result of the map command. Try different output ranges and see what they do.

When you run this sketch, you should see the Mouse Control State message once every time you press the first pushbutton, and the values of the X and Y axes of the joystick, mapped to a range of -5 to 5. You still need to add in the select button on the joystick, however.

Add code to listen for the Joystick Select Button

The joystick select button is a digital input, but it’s wired differently than the buttons you saw in the Digital Lab or the Mouse Control With Pushbuttons Lab.

Previously, you wired the select button to digital input 3. To read the select button in this sketch, add a pinMode command to the setup that makes it an INPUT_PULLUP. Then in the main loop, check if the mosueIsActive variable is true. If it is, then use digitalRead() to read the select button and store it in a local variable called button2State.

Add the following at the end of the setup command:

 // make pin 2 an input, using the built-in pullup resistor:
  pinMode(2, INPUT_PULLUP);

Then at the end of the loop, add the following code:

 if (mouseIsActive == true) {
     // read the second pushbutton:
    int button2State = digitalRead(3);
 }

The select button’s behavior should be like the mouse control pushbutton’s behavior: you only want something to happen when it changes. When the select button changes from off to on, you want it to perform a mouse click. When it changes from on to off, you want it to perform a mouse release. So you need to check for when the select button changes, just like you do with the other pushbutton.

To check for the select button to change, set up a global variable called lastButton2State to save its previous state. Then set up an if statement in the main loop after you read it to see if the current state and the previous state are different. If they are different, add another if statement to see if the current state is HIGH or LOW. If it’s LOW, then print “Mouse press” (remember,its logic is inverted). If the current state is HIGH, then print “mouse press”.

This block of code will look a lot like the code you used for Mouse Control to track the state change of the pushbutton on pin 2.

Add the following line before the setup command:

 int lastButton2State = LOW;       // state of the other button last time you checked

Then inside the if statement that you added to check the mouseIsActive variable, add the following code (the if statement is shown here too):

if (mouseIsActive == true) {
    // read the second pushbutton:
    int button2State = digitalRead(3);

    // if it's changed and it's high, toggle the mouse state:
    if (button2State != lastButton2State) {
      if (button2State == LOW) {
        Serial.println("mouse pressed");
      } 
      else {
        Serial.println("mouse released");
      }
    }
    // save second button state for next comparison:
    lastButton2State = button2State;
  }

When you run this code, you should see the words “mouse pressed” once when you press the select button, and “mouse released” when you release the select button. If it prints continually, you have an error.

When you’ve got that working, you’re ready to take control of the mouse.

Add commands to control the mouse

The Mouse.begin() command is called in the setup. It initializes mouse control from your Leonardo.

Modify the setup by adding the command Mouse.begin(). Then, in the loop where check if mouseIsActive is true, add Mouse.move commands to move as needed. Also add Mouse.press() when the select button is pressed, and Mouse.release() when it is released.

At the end of the setup(), add the following:

  // initialize mouse control:
  Mouse.begin();

Then in the main loop, add the following lines to the if statement that checks mouseIsActive:

   if (mouseIsActive == true) {
    Mouse.move(xAxis, yAxis, 0);

    // read the second pushbutton:
    int button2State = digitalRead(3);

    // if it's changed and it's high, toggle the mouse state:
    if (button2State != lastButton2State) {
      if (button2State == LOW) {
        Serial.println("mouse pressed");
        Mouse.press();
      } 
      else {
        Serial.println("mouse released");
        Mouse.release(); 
      }
    }

That’s the whole sketch. When you run this, press the mouse control pushbutton, then move the joystick and press the select button. You should have full mouse control.

The full sketch for this can be found on the phys comp github repository, called MouseMoveSimpleJoystick.

In this sketch, you can see the value of scaling an analog sensor’s readings to match the output range you need. Since the joystick potentiometers are at rest in the middle of their range, scaling them from -5 to 5 gives you easy control of the mouse movement, which is relative. You can also see how reading the state change of a digital input is important. You’re doing it for two different buttons in this sketch.