My "sense hat" sits ontop of a raspberry pi 3. I've completed the installation instructions found at https://www.raspberrypi.org/documentation/hardware/sense-hat/

lexu:~> sudo apt-get update
lexu:~> sudo apt-get install sense-hat
lexu::~> cp /usr/src/sense-hat/examples ~/ -a
lexu:~> sudo reboot

But when I try to run the 'snake' example, I get a 'Event device not found." - error. Apparently the "joystick" can't be found/read from. Here's the relevant c-code:

    evpoll.fd = open_evdev("Raspberry Pi Sense HAT Joystick");
    if (evpoll.fd < 0) {
            fprintf(stderr, "Event device not found.\n");
            return evpoll.fd;

entering sudo chmod 666 /dev/fd1 fixed the problem!

lexu:~> sudo chmod 666 /dev/fd1

Explanation: The code examples assume that you are running either as root or as a user in that belongs to the group video. My personal user 'lexu' doesn't, so I had to change the access rights.

  • Would in that case useradd -G video lexu not be "more right"? – Ghanima Apr 3 '16 at 13:23
  • @Ghanima: "video" didn't make sense for a joystick, at least for me, but yes, your solution also works. – lexu Apr 3 '16 at 13:57
  • Well, it's the group you named... therefore. – Ghanima Apr 3 '16 at 14:21
  • These types of problems are why they invented the device tree as an alternate way to load modules. A hat is supposed to have an eeprom the has an overlay that adds the hat to the tree in the boot loader. The tree loads modules with a "compatible" statement. It simplifies things, but this site is all about complicated. 😀 – PaulF8080 Apr 14 '17 at 15:49
  • Thanks! Sounds interesting ... Can you provide a link to some documentation? – lexu Apr 18 '17 at 14:56

the group video is required for the LED grid.

the group input is required for the joystick and causes the error mentioned above.

don't forget to relogin after usermod.

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