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The simplest way to connect arcade buttons and a joystick to both a PC and a Raspberry Pi is a USB arcade encoder. Wire each microswitch to the encoder, connect the encoder by USB, and configure the resulting keyboard or gamepad inputs in your operating system and emulator. Direct Raspberry Pi GPIO wiring is also possible when you want a Pi-only build, while legacy DB9 joysticks require a verified, hardware-specific pinout.
This guide explains all three architectures, shows how to wire them safely, and covers controller mapping, input capacity, special controls, and the faults that most often make an arcade panel appear dead.
Choose the connection architecture first
Your host computer and the type of controls you are installing determine the best wiring method. A USB encoder is the most portable option: the same panel can move between a Windows, Linux, or Raspberry Pi system without writing a GPIO driver. Direct GPIO removes the encoder but is tied to a particular Raspberry Pi and software stack. A DB9 joystick is not a universal standard; its signals must be identified before any connection is made.
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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →| Architecture | Host compatibility | Wiring pattern | Software work | Capacity and special controls |
|---|---|---|---|---|
| USB arcade encoder | PC and Raspberry Pi with USB; the I-PAC family supports Linux and Raspberry Pi | Switch wires terminate on labeled encoder inputs; common wires follow the encoder’s ground scheme | Appears as a keyboard or gamepad; no separate PC GPIO driver | An I-PAC2 provides 32 inputs and a dedicated trackball/spinner connector |
| Direct Raspberry Pi GPIO | Raspberry Pi only | One switch side to a GPIO input; the other side to a shared ground rail | Requires a GPIO input method and emulator mapping | Available inputs and driver support depend on the Pi model and software |
| Legacy DB9 joystick | Only after confirming the exact joystick and adapter or GPIO map | Map each connector signal to the intended input and ground | Depends on the adapter, GPIO front end, and emulator | Pin assignments are hardware-specific; do not assume a standard layout |
For a cabinet that may alternate between a PC and a Pi, use a USB encoder. Choose GPIO when the project is deliberately Pi-specific and you want the shortest electrical path. Use a DB9 approach only when preserving an existing joystick is more important than convenience and you can verify its documentation.
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Parts, preparation, and electrical safety
Parts for a USB encoder panel
- Arcade joystick with its four directional microswitches or a Sanwa-style harness.
- Arcade push buttons with microswitches, including start and coin buttons if your cabinet uses them.
- A USB arcade encoder and the wiring harnesses specified by that encoder.
- A USB cable long enough to reach the PC or Raspberry Pi.
- A mounting panel, strain relief, and cable ties so wires cannot pull on switch terminals.
Parts for direct GPIO wiring
- A Raspberry Pi model with the required GPIO header.
- A software image and GPIO input method that support your chosen emulator.
- Jumper wires and, for a temporary build, a mini breadboard. The MakeCode harness materials use a Sanwa-style five-pin joystick, jumper wires, and a breadboard.
- Arcade buttons and a joystick with accessible common and signal terminals.
Before applying power
- Disconnect the USB cable or Pi power supply while making changes.
- Label every wire by function rather than relying only on insulation color. Harness colors are not a universal standard.
- Confirm which terminal is common (COM) and which terminals are normally open switch outputs. A joystick normally has one common and four directional lines, but verify the connector orientation on the exact part.
- Keep Raspberry Pi GPIO at the Pi’s logic level. Never apply 5 V to a GPIO input.
- Plan a shared ground rail for GPIO wiring and check continuity with a meter before powering the board.
Connect arcade controls with a USB encoder
A USB encoder translates physical switch closures into USB keyboard or gamepad events. Ultimarc describes its I-PAC boards as interfaces that connect arcade controls to a host USB port. The I-PAC2 has 32 inputs, supports keyboard and gamepad modes, works generically over USB, and supports Linux and Raspberry Pi systems.
1. Lay out and label the controls
Place the joystick and buttons in the panel, then identify each microswitch: up, down, left, right, the action buttons, start, coin, and any service or escape button. Decide which button will perform an emulator menu or exit function before you close the cabinet. A dedicated escape/menu control is more useful than having to attach a full-size keyboard later.
2. Wire each switch to the encoder
- Turn off the host and unplug the encoder.
- Connect the joystick’s up, down, left, and right signal wires to the encoder terminals labeled for those directions.
- Connect each button’s signal terminal to the encoder input labeled for that button. Use one input per independent switch.
- Connect the common or ground wiring according to the encoder documentation. I-PAC inputs are referenced to ground, so a switch closure pulls the selected input to that reference.
- Secure the harnesses and leave enough slack for the panel to open without stressing a connector.
Do not infer a terminal’s function from its physical position alone. Read the encoder labels and the joystick harness orientation. If a button has two terminals, one is the switch signal and the other is common; reversing them normally does not change the switch electrically, but it can make a harness layout confusing.
3. Connect the encoder to the host
Plug the encoder into a USB port on the PC or Raspberry Pi. In keyboard mode, a press produces the assigned key event; in gamepad mode, the operating system exposes controller buttons and axes. Start with the encoder’s default assignments, especially if they were designed for MAME, and change them only after confirming that every physical input is detected.
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4. Configure RetroPie on first start
- Boot the Raspberry Pi into RetroPie with the encoder connected.
- Follow the controller-configuration prompt that appears during startup.
- When prompted, press the joystick directions, action buttons, start, and coin controls you wired. Assign an unused input to any optional function or skip it when the interface allows.
- Save the configuration, then test the controls in the front end.
RetroPie’s first-start mapping establishes a general controller profile. It does not guarantee that every arcade title uses the same layout.
5. Remap individual games when necessary
Open the emulator’s input configuration while the affected game is running when its controls differ from the default layout. Map the physical buttons to the game’s own actions rather than changing the entire front-end profile for one title. Keep a dedicated escape or menu function available; I-PAC shift functions can provide cabinet commands without adding more visible buttons.
Wire arcade controls directly to Raspberry Pi GPIO
GPIO wiring is a Pi-only design. Each switch is read as an input, and closing the switch connects that input to ground. The exact GPIO software, numbering scheme, and available inputs depend on the Pi model and the image you install.
1. Prepare a common ground
- Identify the joystick common wire and the COM terminals on the push-button microswitches.
- Join those commons into a ground rail. A breadboard can serve as a temporary rail; a soldered distribution point is preferable for a permanent cabinet.
- Connect the ground rail to a Raspberry Pi ground pin.
Adafruit’s direct-control setup states that controls can connect to GPIO and ground without external pull-up resistors in that setup. Follow the input method’s instructions rather than adding pull-ups or pull-downs indiscriminately, because the software and board configuration determine how an unpressed switch is sensed.
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2. Connect individual switch signals
- Connect the remaining terminal of the joystick’s up switch to one GPIO input, down to another, left to another, and right to another.
- Connect one terminal of every action, start, coin, and service button to its own GPIO input.
- Check that no input is accidentally connected to a 5 V rail or to another input.
- Write down the GPIO number and the physical control at both ends of every wire.
A Sanwa-style joystick commonly exposes one common and four directional switch lines through a five-pin connector. Verify the connector orientation and ground wire on the exact joystick instead of trusting a color convention.
3. Configure the GPIO input software
Install or enable the GPIO input driver or front end supported by your Raspberry Pi image, then assign the GPIO numbers to directional and button actions. The driver must present those inputs to the emulator as a usable controller or keyboard device. Once that layer is working, map the controls in RetroPie or the emulator using the same sequence used for a USB controller.
4. Test one input at a time
With the Pi powered, test up, down, left, right, and each button separately in the input utility or configuration screen. A single test is more informative than launching a game with several miswired controls: it reveals whether a fault is electrical, a GPIO-numbering mistake, or an emulator mapping problem.
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DB9 is only a connector shape, not a guaranteed arcade-control pinout. You must identify the exact joystick model or adapter before connecting it to GPIO. A Raspberry Pi Magazine example for a Competition Pro-style joystick assigns DB9 pins 1–4 to up, down, left, and right, pin 6 to fire, and pin 8 to ground, then maps those signals to Raspberry Pi GPIO pins. That assignment applies to that example, not to every DB9 joystick.
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- Find the documentation or a reliable continuity map for the exact joystick.
- With the joystick unplugged, use a meter to confirm which pin closes to ground when each direction or fire button is pressed.
- Record the connector’s pin numbers, signal names, and ground before selecting GPIO inputs.
- Build the adapter or jumper harness so each signal reaches only its intended input.
- Verify the Pi’s GPIO numbering convention in the software configuration; physical header positions and GPIO numbers are not interchangeable labels.
- Power the system only after checking for shorts and confirming that no 5 V signal can reach a GPIO input.
If the joystick behaves unpredictably, stop and recheck the pinout rather than swapping wires while powered. A wrong DB9 assumption can connect a signal to ground or to a voltage source.
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Keyboard mode versus gamepad mode
Keyboard mode is convenient for older emulators and games that already expect key presses. Gamepad mode is preferable when software offers a controller configuration screen and you want distinct button identities. An encoder that supports both lets you choose per host, but changing modes may change which assignments the operating system reports.
Front-end mapping
Map the four directions first, then the action buttons in the order shown by the configuration screen. Assign start and coin explicitly; an arcade cabinet often needs both even when a modern controller profile does not. Save the profile and test navigation in the front end before opening a game.
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Arcade titles can use different action names, button counts, or player assignments. Enter the emulator’s input configuration for a game that does not respond correctly, map the physical controls to that title, and save the game’s profile. Do not overwrite a working global profile to fix one unusual machine layout.
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Input capacity and special controls
Count every independent switch before choosing an encoder: four joystick directions, action buttons, start, coin, service, test, and any second-player controls all consume inputs. The I-PAC2’s 32-input capacity covers a broad two-player digital panel and includes a dedicated trackball/spinner connector. Direct GPIO capacity is not a fixed arcade specification; it depends on the Raspberry Pi header, reserved pins, operating system, and input driver.
Trackballs and spinners are not ordinary push buttons. They generate movement signals and may need the encoder’s dedicated connector or a separate interface. Confirm that your chosen hardware and software can read those signals before drilling the panel. A USB encoder that handles only digital switch closures cannot automatically provide analog or quadrature support simply because spare terminals remain.
Troubleshoot a non-working arcade panel
No controls register at all
- For USB, try another cable and USB port, then check whether the operating system detects a keyboard or gamepad device.
- For GPIO, confirm that the Pi image has the intended GPIO driver enabled and that the ground rail reaches a real Pi ground pin.
- Check that the encoder or Pi is powered only after all wiring is complete.
One direction or button is permanently active
- Inspect for a short between the signal and ground, a bent microswitch tab, or a connector installed one position off.
- Disconnect that switch and test the input with a temporary jumper or the software diagnostic screen.
- On GPIO, verify that the configured input number matches the physical wire and that the input method’s pull configuration is correct.
Directions are swapped
- Recheck the encoder labels against the joystick’s actual switch positions.
- For a five-pin harness, verify orientation and common wire rather than assuming the red or black conductor is ground.
- For DB9, compare every signal with a continuity test and the documented pinout.
Controls work in the menu but not in a game
The hardware and front-end profile are probably functioning. Open that game’s input configuration and assign its actions, including coin and start, to the mapped controls. Check whether the game expects a different player or button order.
The Pi resets or becomes unreliable
- Remove any connection that could feed 5 V into a GPIO input.
- Look for loose ground connections and wires touching adjacent header pins.
- Power down before changing a DB9 or GPIO harness; hot-swapping can create shorts and makes diagnosis harder.
A practical selection checklist
- Need one panel for both PC and Pi: choose a USB encoder.
- Building a Pi-only project and comfortable configuring GPIO: direct GPIO can reduce hardware, but plan the driver and numbering scheme first.
- Reusing an old DB9 joystick: identify and test its exact pinout before selecting an adapter or GPIO map.
- Installing many buttons or two players: total the required inputs and compare them with the encoder’s capacity; the I-PAC2 provides 32.
- Adding a trackball or spinner: select hardware with the appropriate dedicated connector or interface rather than treating it as another switch.
- Operating a cabinet without a keyboard: reserve an escape/menu or service function during the initial wiring and mapping.
Once every switch has a documented signal, a verified common ground, and a saved emulator mapping, the panel is portable and maintainable. Keep the wiring diagram inside the cabinet so a future control change does not require guessing at GPIO numbers, encoder terminals, or DB9 pins.
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