How to Interface Arcade Controls with the Raspberry Pi

Question

Hi guys! As you know, we're putting together a Raspberry Pi-powered arcade machine, so we can live firmly in the past (where all the good stuff happened) and revel in the joys of retro video games!

Among the various challenges we're faced with in adapting our new cabinet is interfacing the controls with a Raspberry Pi, so I thought I'd ask for a few suggestions from the people in the know (that's you).

Joysticks & Buttons

In principle this is a very simple task, because the arcade controls are just micro-switches. They could go straight onto the GPIO pins, with a bit of cunning software running on the Pi to turn the inputs in HID keyboard presses. The emulator recognises these straight out of the box, making it a very neat and efficient way to interface the controls.

However, the problems arise from there not being enough GPIO inputs for the number of controls we need. So what can we do to either increase the number of inputs, or maybe even go in a totally different direction, such as converting it all to use a USB input of kind? Would love to hear some creative suggestions from you guys on the subject.

List of Inputs

Here's a breakdown of the number of inputs we need to get the arcade machine up and running. Each input can just be considered a simple switch -- nothing clever needed with analogue controls or the likes. This is purely on/off digital simplicity. Just a lot of them.

Input Number	Function
1	Player One - Left
2	Player One - Right
3	Player One - Up
4	Player One - Down
5	Player One - Button 1
6	Player One - Button 2
7	Player One - Button 3
8	Player One - Button 4
9	Player One - Button 5
10	Player One - Button 6
11	Player One - Start
12	Player Two - Left
13	Player Two - Right
14	Player Two - Up
15	Player Two - Down
16	Player Two - Button 1
17	Player Two - Button 2
18	Player Two - Button 3
19	Player Two - Button 4
20	Player Two - Button 5
21	Player Two - Button 6
22	Player Two - Start
23	Coin/Credit (a single input from the coin mechanism, rather than one for each player)
24	Exit Game (a button to bring players out of the game, and back to the emulator)
25	Select Game (for choosing a game to play from the emulator's list)
26	Pause
27	Spare (just in case)
28	Spare
29	Spare
30	Spare

Your thoughts on a post card, please!

balearicdynamics · Answer

Hi, let me explain the idea before tracking down the circuit and a decent documentation. First of all take in account that there is an already working software with a set of single-characters commands with the relative parser to connect the ChipKit PI by one side and the Raspberry PI to the other. It works fine and is modular and I can customise it in very few time. So all the input can already send to the PI just the corresponding "command" character. Not only but the parser in this case is monodirectional so the Raspberry PI component side can be simplified. As the console uses almost vintage joysticks and buttons, I suppose that they has also the need to be managed properly to reach the switching quality needed by the micro controller hardware at the date. To simplify the software on the micro we can send already "cleaned" switch signals with a debouncing bank (also the cost is really very few $) with a circuit like the example image below, done for 5 switches (can be expanded as well) Then we should consider that we are working with 30 input switches and the switch detection time is strategic in most of the arcade games. So all the 30 inputs can be read sufficiently fast by a shift-in register (four daisy chained registers can manage up to 32 inputs) so the ChipKit PI as a matter of fact should continuously monitor the four-bytes input status, check if some bit has changed and with some fast AND operations will send the corresponding character to the Raspberry PI. As the communication / parsing protocol on the Raspberry PI receives a CR as the end command it is also possible to send multiple characters if needed to manage simultaneous button press if needed. This is a parameter that can be set at software level. As the Raspberry PI software is developed in C++ it is not difficult to integrate it in Python, as a command line parameter or in any other way (including a background process as it actually works). Enrico

gadget.iom · Answer

Ahh ok. Another approach could be to emulate USB keyboard presses for each button using a commercially available keyboard emulator, or better still an Arduino/Teensy programmed up with the keyboard libraries.