This is the code running on a Teensy LC powering my arcade-style controller. There is 12 buttons in all, same as on a snes controller.
Buttons are managed by a loop on a array of struct, allowing to change the configuration easily. Bounce2 is used to provide accurate typing.
In the current form, the code will make the controller work out of the box with retroarch and other project based on libretro.
| Buttons | Keyboard touch | Pin |
|---|---|---|
| UP | up arrow | 0 |
| RIGHT | right arrow | 1 |
| DOWN | down arrow | 2 |
| LEFT | left arrow | 3 |
| A | x | 4 |
| B | z | 5 |
| X | s | 6 |
| Y | a | 7 |
| L | q | 8 |
| R | w | 9 |
| START | return | 10 |
| SELECT | right shift | 11 |
The configuration is done in the btns array. It's a list of struct tbutton. They take 3 values, an int for the pin, a constant from arduino keyboard library for the keyboard key and a bounce object. The array end with an empty struct whose char is 0.
A teensy LC or 3.2 can handle up to 24 connections. I might be able to make the computer believe there is two gamepad behind a single usb connection while only doing simple stuff. Like in the photos.
A ground wire, the black one, go through every buttons ground tab and back to the teensy ground. Colored wire go from each used pin to the corresponding button. The button's pin is set have a high value. When the button is pressed, the pin is connected to the ground and get a low value. The code simply loop through every pin and check if the button is pressed or not.
A more compact version of thing would use a some kind of matrix. Instead of a common ground, button are hooked to two different pins, one configured as an output, the other as an input. One of the output pin is set high while all the other are set low. Looking at which input is low and which is high can tell which of the button connected at this output.
The naive version is extra simple, making the code dead and circuit dead simple. The matrix version require a bit more of thinking and an extra diode per button to prevent some issue. But it would allow a lot more of button to be connected to the same teensy. While all the 24 pins are required for the 2 gamepad on the naive version, only 10 are needed for the matrix one. And each extra gamepad is only two more pins. And 12 diodes.
Also, LED are diode making light.
Reusing bounce object would save a lot of byte in the tiny ram of these teensy. Also, moving the config into a header file might help.