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Circuit for USB game controller with 12 inputs (8 buttons + 4 directions)
Content: Project overview | Schematic | Programming | Source code | PCB for surface-mount | NeoGeo adapter wiring | Disclaimer
Project overview [hide]
For some projects, a circuit making it possible to connect 12 buttons (including 4 directional buttons) to a PC using an USB port is very useful. Here's a few examples:
  • Home-made Arcade style controller and small arcade cabinets
  • Simple controller (1 wire per button) to USB. Eg: Neo-Geo, Atari...
  • Using appropriate software on the PC side, the inputs can be used for other purposes. Eg: Switches, limit-switches, alarms... A cleaner solution than modifying an existing game controller

On this page, you'll find out how to build such a circuit using a microcontroller. The firmware implements a standard USB joystick with 4 directional buttons and 8 general purpose buttons.

Depending on your skills, you can build the circuit on a breadboard using thru-hole components or build the surface-mount version using my small multiuse PCB2 circuit board. I also sell ready to use circuits and pre-programmed Atmega8 chips (in DIP package only). Visit my online shop for more details.

No drivers required!
That's right, since the USB standard defines device classes. I'm using the human input device (HID) which allows me to tell to the computer that the connected USB device is a joystick and has 2 axis and 4 or 8 buttons. Another nice thing about this is that the adapter should work with all operating systems supporting HID devices. (I tested and it works at least on Win98, Win2K, WinXP and Linux)

This project uses an ATmega8 microcontroller from Atmel. This microcontroller does not support USB in hardware so I used the software-only usb driver from Objective Development. This driver allows an AVR microcontroller such as the ATmega8 to talk USB with minimal external components. As a result, the interface can be built cheaply and easily
Ready to use circuits available

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Schematic [hide]
Here is the main schematic:
main schematic 		And here is a wiring example:
wiring example

Additionally, a wiring table for NeoGeo controllers is shown lower on this page.
Component list:
RefDescription
U2 Atmega8 microcontroller. ATMEGA8-16PC, ATMEGA8-16PI, ATMEGA8-16PJ or ATMEGA8-16PU. Dont use an ATMEGA8L-*, the 12Mhz clock would be too high.
R1 1.5k resistor. Ordinary carbon film 1/4 watt resistors will do.
R2, R3 68 ohm resistors. Ordinary carbon film 1/4 watt resistors will do.
D2, D3 3.6 volts zener diodes.
R4 Do not install, not used anymore.
D1 Do not install, not used anymore.
Y1 12 Mhz crystal.
C2, C3 27 pf capacitors. If the crystal datasheet recommends another value, use it instead.
C1 10uf capacitor. Install it near the ATmega8.
JP1, JP2 Jumpers. You can also use dip switches, ordinary switchs or solder bridges.
J2 6 pin header, 2.54mm spacing. Needed for programming the ATmega8.

For the USB connection, just strip the USB cable and solder the wires directly to the board. USB uses standard wire colors:
Color Description
  Red +5 volts
  Black Ground
  Green D+
  White D-

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Programming the microcontroller [hide]
A microcontroller is a component which must be programmed in order to do something useful. So here is the hexfile which must be flashed into the microcontroller:
usb_game12-1.0.hex

Many microcontrollers have what is called 'Fuse bytes'. In the case of the ATmega8, there are two bytes: The high byte, and the low byte. Those bytes are used to configure some aspects of the microcontroller. What type of clock to use? Crystal? Resonator? Internal RC clock? Allow programming via ISP? It's very important to set the fuses to the right values. Using the wrong values can render your MCU unusable.

For this project, here are the appropriate fuse values:
high byte = 0xc9, low byte = 0x9f

For details about how to program an AVR, visit my AVR programming page.

Pre-programmed Atmega8 (DIP package) available

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Source code [hide]
The source code is released under the GPL license and compiles with avr-gcc. To prevent conflicts, please do not distribute modified version where the USB report descriptor has been modified without replacing the USB Vendor ID and Product ID by yours.

usb_game12-1.0.tar.gz

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Circuit board for surface-mount version [hide]
The surface-mount version uses my Multiuse PCB2 circuit. Here's what it looks like:
Multiuse PCB2:
 Wiring diagram for this project on 'Multiuse PCB2':
Ready to use circuits available

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NeoGeo wiring [hide]
Neo Geo controllers uses standard DB15 connectors. This connector is also used by old PC Joysticks but it incompatible. Here's a table describing how to wire a Neo Geo controller connector to this circuit:
DB15 pinNeo Geo nameUSB Game12 nameComments
1 Common Common
3 Select Button 5
4 D Button Button 3
5 B Button Button 1
6 Right Right
7 Down Down
8 +5v +5v Only for some controllers
9 D Button Button 3 Duplicates pin 4
11 Start Button 4
12 C button Button 2
13 A button Button 0
14 Left Left
15 Up Up
(DB15 pins 2 and 10 are not connected)

Disclaimer [hide]
I cannot be held responsible for any damages that could occur to you or your equipment while following the procedures present on this page. Also, I GIVE ABSOLUTELY NO WARRANTY on the correctness and usability of the informations on this page. Please note, however, that the procedures above have worked in my case without any damages or problems.

Now you cannot say that I did not warn you :)

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