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The source code and some artwork files are available from my local download or from github.com/larsi-org/MAME-Interface

I decided to build only a single player controller with just one joystick and a few buttons. After a whole day of on-line "research" I decided to have 6 play buttons (instead of 8), 2 Player1 control buttons, and 4 system control buttons. I use the following mapping:

#	Function	Keyboard Code	Teensy Pin	Teensy Port
1	Player1 Up	Up	0	PB0
2	Player1 Down	Down	1	PB1
3	Player1 Left	Left	2	PB2
4	Player1 Right	Right	3	PB3
5	Player1 Button1	L-Ctrl	4	PB7
6	Player1 Button2	L-Alt	5	PD0
7	Player1 Button3	Space	6	PD1
8	Player1 Button4	L-Shift	7	PD2
9	Player1 Button5	Z	12	PD7
10	Player1 Button6	X	13	PB4
11	Player1 Start	1	14	PB5
12	Player1 Coin	5	15	PB6
13	Pause	P	16	PF7
14	UI Select	Enter	17	PF6
15	UI Cancel	Esc	18	PF5
16	Config Menu	Tab	19	PF4

That means I have a total of 16 inputs. I want to use some buttons multiple times - Button1 is used again under the 6 buttons (as a fake 7th button for NeoGeo games) and Button1 and Button2 are also on the left and right for Pinball games. So I need a total 9 play buttons which are all red. The control buttons are all white with the exception of the Player1 Start button, which has a special symbol.

There are many great sites where you can buy all kinds of buttons and joysticks, like Ultimarc, ArcadeShop.de, Suzo-Happ, or X-Arcade. I decided to use SparkFun's Short Handle Arcade Joystick and Suzo-Happ's Competition Pushbutton for the play buttons and the regular Pushbutton for the control buttons.

The next step was to find an enclosure for the button, the joystick, and the electronics. I wanted something better than a plastic box, maybe something a little more steampunk... After looking around I settled for getting a "Vintage Wooden Lap Desk" on eBay. The slightly slanted surface is perfect. I applied my layout by printing it out and marking the center holes with a pushpin. After this I started with a small drill and went up a few steps until I had drilled all holes with a ¼" drill. The last step was to drill with a 1 1/8 " drill, which was more difficult than I anticipated. I had to recharge the drill a few times and unfortunately the holes were not as clean as I had hoped. Basically I had scratched the top surface badly.

To hide my mistakes from the last drilling and to label the button I decided to decoupage some paper on top of the wood (check out the download section). I had to cleanup the wooden surface and glue the mask over it. The next day I sealed the surface and I repeated the sealing process the next two days.

I thought about just using the popular I-PAC 2 or the easy to use Arcade Controller. After reading about the V-USB project and related sub projects (like Tinkerlog's Tupperware Arcade Controls) I wanted to to design my own. But then I found this great little board called Teensy. You can buy it from adafruit for $20. It works perfectly well with the Arduino interface, but you have to download the Teensyduino patch for your Arduino version and the Teensyloader. Here is a really nice tutorial and here is my source for the MAME system (check out the download section):

#define REPEATRATE 100 // milliseconds

const byte pin_P1_UP     =  0;
const byte pin_P1_DOWN   =  1;
const byte pin_P1_LEFT   =  2;
const byte pin_P1_RIGHT  =  3;

const byte pin_P1_B1     =  4;
const byte pin_P1_B2     =  5;
const byte pin_P1_B3     =  6;
const byte pin_P1_B4     =  7;
const byte pin_P1_B5     = 12;
const byte pin_P1_B6     = 13;

const byte pin_P1_START  = 14;
const byte pin_P1_COIN   = 15;
const byte pin_PAUSE     = 16;
const byte pin_SELECT    = 17;
const byte pin_CANCEL    = 18;
const byte pin_CONFIG    = 19;

const byte pin_LEDOutput = 11;

//Variables for the states of the MAME buttons
byte buttons[] = {
  pin_P1_UP, pin_P1_DOWN, pin_P1_LEFT, pin_P1_RIGHT,
  pin_P1_B1, pin_P1_B2, pin_P1_B3, pin_P1_B4, pin_P1_B5, pin_P1_B6,
  pin_P1_START, pin_P1_COIN, pin_PAUSE, pin_SELECT, pin_CANCEL, pin_CONFIG
};

byte keys[] = {
  KEY_UP, KEY_DOWN, KEY_LEFT, KEY_RIGHT,
  KEY_A, KEY_S, KEY_D, KEY_Z, KEY_X, KEY_C,
  KEY_1, KEY_5, KEY_P, KEY_ENTER, KEY_ESC, KEY_TAB
};

#define NUMBUTTONS sizeof(buttons)

void setup()
{
  //Setup the pin modes.
  pinMode( pin_LEDOutput, OUTPUT );

  //Special for the Teensy is the INPUT_PULLUP
  //It enables a pullup resitor on the pin.
  for (byte i = 0; i < NUMBUTTONS; i++) {
    pinMode(buttons[i], INPUT_PULLUP);
  }
}

void loop()
{
  // //debugging the start button...
  digitalWrite ( pin_LEDOutput, digitalRead(pin_P1_START));

  //Progess the MAME controller buttons to send keystrokes.
  fcnProcessButtons();
}

//Function to process the buttons from the SNES controller
void fcnProcessButtons()
{
  static long currentkey = 0;
  byte nothingpressed = 1;

  // run through all the buttons
  for (byte i = 0; i < NUMBUTTONS; i++) {

    // are any of them pressed?
    if (! digitalRead(buttons[i])) {
      nothingpressed = 0; // at least one button is pressed!

      // if its a new button, release the old one, and press the new one
      if (currentkey != keys[i]) {
        Keyboard.set_key1(0);
        Keyboard.send_now();
        Keyboard.set_key1(keys[i]);
        currentkey = keys[i];
        Keyboard.send_now();
      } 
      else {
        // the same button is pressed, so repeat!
        Keyboard.set_key1(keys[i]);
        Keyboard.send_now();
        delay(REPEATRATE);
      }
    }
  }

  if (nothingpressed) {
    // release all keys
    Keyboard.set_key1(0);
    Keyboard.send_now();
  }
}

First I thought of a very simple and solderless method to wire up all the buttons. I bought a 100 pack of female .187 solderless terminals and 2 × 40 pin male break away header. I removed the plastic part of terminals and cut up the headers so that I have 2 pin connectors. Both parts can be crimped together with some pliers.

This did work, but sometimes the connection got loose, so I decided to just solder the 2 pin connectors directly to the switches. I have 15 buttons and 1 joystick (4 buttons) and I need 2 of these connectors for each buttons, which means I had to solder 38 connectors.

The buttons can be connected to the controller board with dual-female jumper wire. Because I have 2 pins, I can easily daisy chain all button grounds to just a single ground to the controller board.

I can also daisy chain the triple button B1 and the double button B2 and connect the rest with dual-female jumper wire. I used some 4 pin to 4 × 1 pin cables that allowed me to connect the the buttons in groups of 4 to the controller board.

I learnt a lot. About woodwork, decoupage, PCBs, and electronics. I spent 12 hours and a total of $100 on this controller. I think next time I might just get a X-Arcade Dual for $130... Or maybe not