Arduino Retro Computer: Joystick Interface

The joystick itself contains no logic - it's just push buttons and potentiometers. The brains of the input reside in the Arduino.

Some very good references on how to read analog and digital input on the Arduino:

http://arduino.cc/en/Tutorial/ReadAnalogVoltage
http://arduino.cc/en/tutorial/button
http://arduino.cc/en/Reference/Constants

Basically, we can't just wire from 5V through a push button then to the data input pin; we must use a pull-up (or pull-down) resistor. The critical piece for the push buttons from those references is as follows: "If you have your pin configured as an INPUT, and are reading a switch, when the switch is in the open state the input pin will be "floating", resulting in unpredictable results. In order to assure a proper reading when the switch is open, a pull-up or pull-down resistor must be used. The purpose of this resistor is to pull the pin to a known state when the switch is open. A 10 K ohm resistor is usually chosen, as it is a low enough value to reliably prevent a floating input, and at the same time a high enough value to not not draw too much current when the switch is closed."

Hardware

9-Position Female D-Sub Connector (Radio Shack #276-1538)

5x 10k Ohm Resistor

Breadboard

Wiring

The wiring for the select button is different than the 4 push buttons. The Joystick Breakout Board shorts Select (S1) to GND when the stick is pressed in. To read this, Select is wired with a pull-up resistor while the others are with pull-down.

Wiring Schematic:

Created with http://www.digikey.com/schemeit

The pin layout for the serial cable is as follows:

#1 S1 (Stick Select Button)
#2 S2 (Right Button)
#3 S3 (Top Button)
#4 S4 (Left Button)
#5 S5 (Bottom Button)
#6 Vcc
#7 Analog Xout
#8 Analog Yout
#9 GND

Code

I created a Joystick Class in my operating system code to ease in interfacing:
class JoystickModel
{
  private:
  int buttonPinSelect;
  int buttonPinRight;
  int buttonPinTop;
  int buttonPinLeft;
  int buttonPinBottom;
  int analogPinX;
  int analogPinY;

  public:
  bool init(int newButtonPinSelect, int newButtonPinRight, int newButtonPinTop, int newButtonPinLeft, int newButtonPinBottom,
            int newAnalogPinX, int newAnalogPinY)
  {
    buttonPinSelect = newButtonPinSelect;
    buttonPinRight = newButtonPinRight;
    buttonPinTop = newButtonPinTop;
    buttonPinLeft = newButtonPinLeft;
    buttonPinBottom = newButtonPinBottom;
    
    pinMode(buttonPinSelect, INPUT);
    pinMode(buttonPinRight, INPUT);
    pinMode(buttonPinTop, INPUT);
    pinMode(buttonPinLeft, INPUT);
    pinMode(buttonPinBottom, INPUT);

    analogPinX = newAnalogPinX;
    analogPinY = newAnalogPinY;
       
    return true;
  }
  
  bool selectPressed()
  {
    // Returns true if button is pressed.
    // Select button uses LOW because the joystick breakout shorts to ground with select.
    return (digitalRead(buttonPinSelect) == LOW);
  }
  
  bool leftPressed()
  {
    // Returns true if button is pressed.
    return (digitalRead(buttonPinLeft) == HIGH);
  }
  
  bool topPressed()
  {
    // Returns true if button is pressed.
    return (digitalRead(buttonPinTop) == HIGH);
  }
  
  bool rightPressed()
  {
    // Returns true if button is pressed.
    return (digitalRead(buttonPinRight) == HIGH);
  }
  
  bool bottomPressed()
  {
    // Returns true if button is pressed.
    return (digitalRead(buttonPinBottom) == HIGH);
  }
  
  float analogX()
  {
    // Returns position of stick between -1 and 1.
    // Take - as X potentiometer is mounted reversed on controller.
    return -(((float)analogRead(analogPinX) / 512.0) - 1.0);
  }
  
  float analogY()
  {
    // Returns position of stick between -1 and 1.
    // Take - as Y potentiometer is mounted reversed on controller.
    return -(((float)analogRead(analogPinY) / 512.0) - 1.0);
  }
};

Global:
const int Joystick1SelectPin = 3;
const int Joystick1RightPin = 4;
const int Joystick1TopPin = 5;
const int Joystick1LeftPin = 6;
const int Joystick1BottomPin = 7;
const int Joystick1AnalogX = 0;
const int Joystick1AnalogY = 1;

const byte numberOfJoysticks = 2;
JoystickModel joysticks[numberOfJoysticks];

Inside setup():
  joysticks[0].init(Joystick1SelectPin, Joystick1RightPin, Joystick1TopPin, 
                    Joystick1LeftPin, Joystick1BottomPin, Joystick1AnalogX, Joystick1AnalogY);

Inside loop():
  float analogX = joysticks[0].analogX();
  float analogY = joysticks[0].analogY();
  char analogXString[10];
  char analogYString[10];
  dtostrf(analogX, 5, 3, analogXString);
  dtostrf(analogY, 5, 3, analogYString);
  Serial.print("Analog X: ");
  Serial.print(analogXString);
  Serial.print(" Analog Y: ");
  Serial.print(analogYString);

  if (joysticks[0].selectPressed())
  {
    Serial.print(" Select Pressed");
  }
  if (joysticks[0].rightPressed())
  {
    Serial.print(" Right Pressed");
  }
  if (joysticks[0].topPressed())
  {
    Serial.print(" Top Pressed");
  }
  if (joysticks[0].leftPressed())
  {
    Serial.print(" Left Pressed");
  }
  if (joysticks[0].bottomPressed())
  {
    Serial.print(" Bottom Pressed");
  }
  Serial.println("");

Output from the console:

Asteroids + Controller

I wanted to play the Asteroids game with my new controller, so I made the following changes to the game code to get it to work:

Replaced controller_init() with:
static void controller_init()
{
  // Configure input pins with internal pullups
  pinMode(6, INPUT);
  pinMode(7, INPUT);
}

Replaced controller_sense() with:

static byte controller_sense(uint16_t clock)

{

  byte r = 0;

  if (digitalRead(6))

  {

    r |= CONTROL_UP;

  }

  if (digitalRead(7))

  {

    r |= CONTROL_DOWN;

  }

  return r;

}

In static void handle_player(byte i, byte state, uint16_t clock), there is a line:

    char rotate = (512 - analogRead(0)) / 400;

Since my stick is reversed, I just had to make that negative:

    char rotate = -(512 - analogRead(0)) / 400;

Copyright (c) 2015 Clinton Kam
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