I found these instructions on how to turn a TI graphing calculator into an interval timer. The instructions are for cameras that have 2.5mm plugs for the shutter release connector (eg. Rebel series), but it's not hard to adapt this to other connectors.

For a TI-83/84
http://www.instructables.com/id/Turn...omet/?ALLSTEPS

For a TI-89
http://code.coneybeare.net/posts/32-...I89-Calculator

Originally Posted by b84wm

haha, awesome. in high school i was stoked to hax0r my Ti and play tetris on it.

I was the coolest kid in 7th grade with the TI-85 that plays games.

I suck with that stuff. But I still have the ti-85 and it still plays games, so the latter is correct tense.