I recently bought a set of 24 TI-Nspire keypads for about $5, so I sacrificed one to science. Here's what's inside the Nspire keypad: from left to right, the front cover with the larger keys, the membrane with the small alphabetic and secondary math keys, the mainboard, and the back cover. Note the metal plate that the latching mechanism latches into to hold the keypad securely. The PCB in the keypad appears to have four test points, three of which are labelled SP1-SP3 and one of which is unlabelled, but since they don't appear to connect electrically with any traces, I believe they're used for aligning the keypad PCB in some test jig. The edge connector has an intriguing number of unused pins, as willrandship mentioned. I also found it interesting that the directional pad actually has contacts and corresponding plastic pins for eight directions, rather than simply reading the combination of two cardinal directions as a diagonal.

Other than reselling these as individual keypads, and using two of them for my TI-Nspire calculators that had only TI-84 Plus keypads, what should I do with these? Is there anything I could do to use them for interesting projects? I cross-posted this information in willrandship's topic about an unfinished Nspire project, but it doesn't seem like the full pinout of the keypad has been determined yet.

Click for full-sized image

How permeable is the membrane to light? It might be interesting to try to make an LED-backlit Nspire keypad.

I'm also mildly amused by the ASIC_NATIVE_KB legend silkscreened on the board.

It should be noted that the pinout is really, as far as I can tell, just a whole bunch of I/O ports. The keypads use a matrix-style method of reading every row at a time, and the rows are clearly visible from the layout of the RAM that the keyboard state is stored in.

Practically speaking, if you want to do some fun hardware mods, what you're looking at is a huge amount of free I/O. The unused pins are likely I/O as well, but I'd like to confirm that with some simple code. Vogtinator would probably know a lot more about it, considering he was the one who wrote the I/O driver for the SoC for linucx.

As far as lights go, you'd probably be better off cutting holes for the LEDs. The membrane's not very translucent. That would be pretty cool, though, especially if you made them charlieplexed so you could light them up by row or individually with the leftover pins.

I still love the idea of having a PS/2 port (configured internally to use pullups and some kind of voltage booster, although apparently PS/2 is relatively tolerant to bad voltages) and having a bunch of other I/O available for other things. Have an oscilloscope program that reads from 16 channels at 30 MHz and draws it on the screen, or a flash programmer with emulation support for whatever you're programming.

Does somebody know the pinout for the keypad?

I found this thread on another forum, hope it's helpful.