What idiot put that there?

Attempting to chart an USB keyboard controller turned out to be a bigger challenge than expected. The story is simple. I have a dance mat, which uses a PS/2 passthrough connector. I have however been unable to get it to work, and in order to bring it up on its feet, I have killed an old USB keyboard and stripped the controller from it.

Keyboards work by mapping each button to a matrix of inputs, simply put separated in rows and columns, but unrelated to the actual button layout. If you have ever taken apart a keyboard, this mapping is done by the thin plastic film found inside. The controller I have consists of 9 rows and 18 columns, and for the mapping I use my faithful multimeter.

Going through the rows, it started out well as I found the "volume mute" button as well as a few arrow keys and letters. Then, the computer started grinding and hibernated. I scratched my head and restarted it, finding that the button I managed to trigger was the sleep button. Excellent. I went into the power settings and disabled the sleep button (told it to ask me first, so I would at least know when I accidentally trigged it). Moving on, I managed to do the same thing again, however this time triggering the shutdown button.

Seriously, what idiot thought it would be a good idea to have a shutdown button on a keyboard? Stupidity!