Integrate keypads and gamepads into your next project
In Control
The Python evdev library offers a simple way to connect input devices, even if you don't know the key bindings.
Keypads and gamepads can be good solutions for projects that have requirements for simplicity, small form factor, or more rugged operation. Companies like Sony (PS2/PS3) and Logitech, and even makers of generic clones, offer a number of keypads and gamepads for USB wired or wireless products (Figure 1).
Although the Python Pygame library offers a generic keyboard and joystick interface, I found the python-evdev library to be a little simpler and more straightforward.
python-evdev
The python-evdev library [1] provides bindings to the generic input event interface in Linux. The evdev interface passes events generated in the kernel, typically located in /dev/input/
.
To install python-evdev on a Debian-compatible operating system, enter:
sudo apt-get install python-evdev
Not all keypad and gamepad buttons are mapped consistently, so a simple test program is needed to find the keycodes (Listing 1) [2]. For most small systems, the controller's USB connection will be on /dev/input/event0
; on larger systems, event1
or event2
might be the input device. When a key is pressed, the test program outputs the time, keycode, and an alias for the key binding (Listing 2).
Listing 1
keys_evdev.py
Listing 2
Test Program Output
At a minimum, most keypads or gamepads will have the buttons: A, B, X, Y, Start, Select, Left Shoulder, and Right Shoulder. The code in Listing 3 captures these buttons.
Listing 3
gamepad_evdev.py
Summary
With the sample code provided here, you have a starting point for your next kiosk, robotics, or game project; for example, my daughter and I used the evdev interface with a Raspberry Pi to control a two-axis crane (Figure 2).
Infos
- python-evdev: http://python-evdev.readthedocs.io/en/latest/#
- Listings for this article: ftp://ftp.linux-magazine.com/pub/listings/linux-magazine.com/207
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