Classic Joystick to USB Adaptor using Arduino

• Arduino Leonardo – http://arduino.cc/en/Main/ArduinoBoardLeonardo or Arduino Micro – http://arduino.cc/en/Main/ArduinoBoardMicro
• 9-Position HD Male D-Sub Connector – http://www.radioshack.com/product/index.jsp?productId=2102497 or equivalent
• Wire
• Classic Console Joystick

Step 2: Hardware

Connect the pins of the D-Sub Male 9 Position connector to the pins of the Arduino Leonardo or Arduino Micro as shown in the table.

Step 3: Software

The following Arduino Sketch file should be compiled and uploaded into the Arduino Leonardo or Arduino Micro: JoystickToKeyboard.ino

// ColecoVision / ADAM Joystick to PC Keyboard Converter
// for the Arduino Leonardo
// 2014-08-24
//----------------------------------------------------------------------------------

// Joystick Pins
const byte gcFirePin = 2;
const byte gcUpPin = 3;
const byte gcDownPin = 4;
const byte gcLeftPin = 5;
const byte gcRightPin = 6;
const byte gcModeAPin = 7;
const byte gcModeBPin = 8;
const byte gcFireMonitorPin = 13;
const byte gcBit0Pin = 3;
const byte gcBit2Pin = 4;
const byte gcBit3Pin = 5;
const byte gcBit1Pin = 6;

// Keyboard Keys
const char gcUpKey = KEY_UP_ARROW;
const char gcDownKey = KEY_DOWN_ARROW;
const char gcLeftKey = KEY_LEFT_ARROW;
const char gcRightKey = KEY_RIGHT_ARROW;
const char gcLeftFireKey = KEY_LEFT_ALT;
const char gcRightFireKey = KEY_LEFT_CTRL;
const char gcPurpleButtonKey = KEY_LEFT_SHIFT;
const char gcBlueButtonKey = 'z';
const char gcAsteriskKey = '-';
const char gcPoundKey = '=';

// Current Frame Joystick Status
byte gLeftFireButton = 0;
byte gRightFireButton = 0;
byte gUp = 0;
byte gDown = 0;
byte gLeft = 0;
byte gRight = 0;
char gNumPadValue = ' ';
byte gPurpleButton = 0;
byte gBlueButton = 0;
byte gBit0 = 0;
byte gBit1 = 0;
byte gBit2 = 0;
byte gBit3 = 0;

// Last Frame Joystick Status
byte gLastLeftFireButton = 0;
byte gLastRightFireButton = 0;
byte gLastUp = 0;
byte gLastDown = 0;
byte gLastLeft = 0;
byte gLastRight = 0;
char gLastNumPadValue = ' ';
byte gLastPurpleButton = 0;
byte gLastBlueButton = 0;

// Line Read Variables
const unsigned int gcThreashold = 4;
unsigned int gLeftFireCount = 0;
unsigned int gRightFireCount = 0;
unsigned int gUpCount = 0;
unsigned int gDownCount = 0;
unsigned int gLeftCount = 0;
unsigned int gRightCount = 0;
unsigned int gBit0Count = 0;
unsigned int gBit1Count = 0;
unsigned int gBit2Count = 0;
unsigned int gBit3Count = 0;

// Frame Variables
const int gcFrameLength = 10;
unsigned int gLoopsPerFrame = 0;
unsigned long gLastFrameStart = 0;

// Shows the status of the joystick.
void ShowJoystickStatus()
{
  // Debug Information
//  Serial.println(gLoopsPerFrame);
  digitalWrite(gcFireMonitorPin, gLeftFireButton | gRightFireButton);
}

void SendKeyboardStateToPc()
{
  if ((gLastNumPadValue != ' ') && (gLastNumPadValue != gNumPadValue))
  {
    Keyboard.release(gLastNumPadValue);
  }
  if ((gNumPadValue != ' ') && (gLastNumPadValue != gNumPadValue))
  {
    Keyboard.press(gNumPadValue);
  }
  
  SendLineStateToPc(gLastLeftFireButton, gLeftFireButton, gcLeftFireKey);
  SendLineStateToPc(gLastRightFireButton, gRightFireButton, gcRightFireKey);
  SendLineStateToPc(gLastUp, gUp, gcUpKey);
  SendLineStateToPc(gLastDown, gDown, gcDownKey);
  SendLineStateToPc(gLastLeft, gLeft, gcLeftKey);
  SendLineStateToPc(gLastRight, gRight, gcRightKey);
  SendLineStateToPc(gLastPurpleButton, gPurpleButton, gcPurpleButtonKey);
  SendLineStateToPc(gLastBlueButton, gBlueButton, gcBlueButtonKey);
}

void SendLineStateToPc(byte lastState, byte currentState, char keyUsedForLine)
{
  if ((lastState == 1) && (currentState == 0))
  {
    Keyboard.release(keyUsedForLine);
  }
  if ((lastState == 0) && (currentState == 1))
  {
    Keyboard.press(keyUsedForLine);
  }
}

unsigned int CheckJoystickLine(byte pin)
{
  return (digitalRead(pin) == LOW);
}

void CheckJoystickLines()
{
  const int cLineDelay = 50;
  
  // Put Joystick in Direction Mode
  digitalWrite(gcModeAPin, HIGH);
  digitalWrite(gcModeBPin, LOW);
  delayMicroseconds(cLineDelay);
  gLeftFireCount += CheckJoystickLine(gcFirePin);
  gUpCount += CheckJoystickLine(gcUpPin);
  gDownCount += CheckJoystickLine(gcDownPin);
  gLeftCount += CheckJoystickLine(gcLeftPin);
  gRightCount += CheckJoystickLine(gcRightPin);
  // Put Joystick in Keypad Mode
  digitalWrite(gcModeAPin, LOW);
  digitalWrite(gcModeBPin, HIGH);
  delayMicroseconds(cLineDelay);
  gRightFireCount += CheckJoystickLine(gcFirePin);
  gBit0Count += CheckJoystickLine(gcBit0Pin);
  gBit1Count += CheckJoystickLine(gcBit1Pin);
  gBit2Count += CheckJoystickLine(gcBit2Pin);
  gBit3Count += CheckJoystickLine(gcBit3Pin);
}

void ResetFrameVariables()
{
  // Copy Current Frame to Last Frame
  gLastNumPadValue = gNumPadValue;
  gLastLeftFireButton = gLeftFireButton;
  gLastRightFireButton = gRightFireButton;
  gLastUp = gUp;
  gLastDown = gDown;
  gLastLeft = gLeft;
  gLastRight = gRight;
  gLastPurpleButton = gPurpleButton;
  gLastBlueButton = gBlueButton;
  
  // Reset Frame Loop Counter
  gLoopsPerFrame = 0;
  
  // Reset Joysick State
  gLeftFireCount = 0;
  gLeftFireButton = 0;
  gRightFireCount = 0;
  gRightFireButton = 0;
  gUpCount = 0;
  gUp = 0;
  gDownCount = 0;
  gDown = 0;
  gLeftCount = 0;
  gLeft = 0;
  gRightCount = 0;
  gRight = 0;
  gBit0Count = 0;
  gBit0 = 0;
  gBit1Count = 0;
  gBit1 = 0;
  gBit2Count = 0;
  gBit2 = 0;
  gBit3Count = 0;
  gBit3 = 0;
  gNumPadValue = ' ';
  gPurpleButton = 0;
  gBlueButton = 0;
}

byte DetermineJoystickLineValue(unsigned int pressCount)
{
    return (pressCount >= gcThreashold);
}

void DetermineJoystickValues()
{
  const char cKeypadValueLookup[16] = {
    ' ', '6', '1', '3', '9', '0', gcAsteriskKey, ' ', 
    '2', gcPoundKey, '7', ' ', '5', '4', '8', ' '};
    
  gLeftFireButton = DetermineJoystickLineValue(gLeftFireCount);
  gRightFireButton = DetermineJoystickLineValue(gRightFireCount);
  gUp = DetermineJoystickLineValue(gUpCount);
  gDown = DetermineJoystickLineValue(gDownCount);
  gLeft = DetermineJoystickLineValue(gLeftCount);
  gRight = DetermineJoystickLineValue(gRightCount);
  
  gBit0 = DetermineJoystickLineValue(gBit0Count);
  gBit1 = DetermineJoystickLineValue(gBit1Count);
  gBit2 = DetermineJoystickLineValue(gBit2Count);
  gBit3 = DetermineJoystickLineValue(gBit3Count);
  
  int keypadCode = (gBit3 << 3) + (gBit2 << 2) + (gBit1 << 1) + gBit0;
  
  gNumPadValue = cKeypadValueLookup[keypadCode];
  
  // Check for SuperAction Controller Buttons.
  if (keypadCode == 7)
  {
    gPurpleButton = 1;
  }
  if (keypadCode == 11)
  {
    gBlueButton = 1;
  }
}

void setup()
{
  // Setup Serial Monitor
//  Serial.begin(19200);
  
  // Setup Joystick Pins
  pinMode(gcFirePin, INPUT_PULLUP);
  pinMode(gcUpPin, INPUT_PULLUP);
  pinMode(gcDownPin, INPUT_PULLUP);
  pinMode(gcLeftPin, INPUT_PULLUP);
  pinMode(gcRightPin, INPUT_PULLUP);
  pinMode(gcModeAPin, OUTPUT);
  pinMode(gcModeBPin, OUTPUT);
  pinMode(gcFireMonitorPin, OUTPUT);
}

void loop()
{
  unsigned long currentTime;
  
  currentTime = millis();
  if (currentTime >= (gLastFrameStart + gcFrameLength))
  {
    // Do Joystick Value Commit Logic
    DetermineJoystickValues();
    
    // Send Values to Monitor
    ShowJoystickStatus();
    
    // Send Keyboad State to the PC
    SendKeyboardStateToPc();
    
    // Reset Frame Variables
    ResetFrameVariables();
  
    // Time to start next frame
    gLastFrameStart = currentTime;
  }
  else
  {
    // Check the value of the input lines and make note of them.
    gLoopsPerFrame++;
    CheckJoystickLines();
  }
}

For more detail: Classic Joystick to USB Adaptor using Arduino