Arduino Leonardo code to behave as a keyboard with pins set to MAME-ish key bindings.

arcade.ino

#include <Keyboard.h>

// MAMEish. An array of pin-key pairs.
struct { int pin; int key; } pinsToKeys[] = {
  { 2,  KEY_LEFT_ARROW  },
  { 3,  KEY_UP_ARROW    },
  { 4,  KEY_RIGHT_ARROW },
  { 5,  KEY_DOWN_ARROW  },
  { 6,  KEY_LEFT_CTRL }, // Fire 1
  { 7,  KEY_LEFT_ALT  }, // Fire 2
  { 8,  ' ' },           // Fire 3
  { 9,  'a' },           // Fire 4
  { 10, 's' },           // Fire 5
  { 11, 'q' },           // Fire 6
  { A0, '1' },           // start
  { A1, KEY_ESC }        // select
};

void setup() {
  // Set all used pins to handle input from
  // arcade buttons.
  for (auto const &pinToKey : pinsToKeys) {
    pinMode(pinToKey.pin, INPUT_PULLUP);
  }

  // Initialize keyboard.
  Keyboard.begin();
}

void loop() {
  // For each pin-key pair, check the state
  // of the pin and set the associated key
  // state to match.
  for (auto const &pinToKey : pinsToKeys) {
    if (digitalRead(pinToKey.pin) == LOW) {
      Keyboard.press(pinToKey.key);
    } else {
      Keyboard.release(pinToKey.key);
    }
  }
}

First of all I would like to thank you for providing a simplistic code for Mame arcade controller.
I am a complete beginner with no programming and Arduino skills. But in the last few days I tried to read a lot of stuff available, specially yours, regarding it to start my journey with it.

As this is my first project, I plans to make a simple USB keyboard/Mame arcade stick which I am going to use for other PC games like Devil May Cry3 as well. So I figured, I need 4 directional keys, 8 action buttons, 2 keys for start & coin, Escape and Enter key (just like in computer keyboard). So in total,16 keys.

As I found out that Arduino Leonardo can be emulated as USB keyboard and it provides you with 20 digital I/O keys. I am trying to use your code (which I modified as per my own need) but I am not sure if it is correct or not.

I already brought Arduino Leonardo chip and arcade control stick and buttons to move forward with my project.

Kindly check if it will be possible for me to use the analog keys as digital by emulating it as USB keyboard for my arcade controller and it should act as 0 delay keyboard encoder.

#include <Keyboard.h>

// MAMEish. An array of pin-key pairs.
struct { int pin; int key; } pinsToKeys[] = {
{ 2, KEY_LEFT_ARROW },
{ 3, KEY_UP_ARROW },
{ 4, KEY_RIGHT_ARROW },
{ 5, KEY_DOWN_ARROW },
{ 6, 's' }, // Fire 1
{ 7, 'd' }, // Fire 2
{ 8, 'f' }, // Fire 3
{ 9, 'x' }, // Fire 4
{ 10, 'c' }, // Fire 5
{ 11, 'v' }, // Fire 6
{ 12, 'g' }, // Button 7
{ 13, 'b' } // Button 8

{ A0, '1' } // select

{ A1, '5' } // Coin

{ A2, KEY_ESC } // Back

{ A3, KEY_RETURN } // Confirm Actions/Activate
};

void setup() {
// Set all used pins to handle input from
// arcade buttons.
for (auto const &pinToKey : pinsToKeys) {
pinMode(pinToKey.pin, INPUT_PULLUP);
}

// Initialize keyboard.
Keyboard.begin();
}

void loop() {
// For each pin-key pair, check the state
// of the pin and set the associated key
// state to match.
for (auto const &pinToKey : pinsToKeys) {
if (digitalRead(pinToKey.pin) == LOW) {
Keyboard.press(pinToKey.key);
} else {

Keyboard.release(pinkey.key);
    }

  }

}

It's been a while since I wrote this, but I don't see anything wrong with your code. The analogue pins of a Leonardo can all be assigned as digital inputs too. I'd be careful of using pin 13 though. It's a little different to the other digital pins (I forget why exactly but I think it's to do with the LED).

You'll need to wire each pin to an arcade switch, and the other pin of each switch to a ground pin on the Leonardo. You can safely wire all the ground pins to a single ground of the arduino.

After programming the Leonardo, you should only need to use a USB lead to plug it into a computer. It should be recognised as a keyboard.