I ended up getting my order of parts for my calculator, which I'm thinking of calling a Hackulator. One of the things I ordered was a mini HDMI port extender so I can hook it up to a monitor without taking apart the calculator and without having all of the ports exposed (though it is still an option at this point). I took all of the boards and the battery and I was able to fit them inside the case. After a little bit of moving items around inside, I'm pretty sure I know where I want all of the boards. For the new display board, I am able to fit it right behind the LCD display, so the extension cable is no longer necessary. Also, it feels like it weighs just a little less than a real TI calculator with batteries.

I looked at the new display board and made note of all of the pins it uses in a spreadsheet and then I did the same for the audio board I got. It turns out that the audio board and the backlight want to use the same pin, so I cut a little trace that's meant to be cut on the display board. I still have the option of using a different PWM pin (GPIO13) if I want to resolder the and hook it up to a different wire. That would leave 15 free GPIO pins if I still use GPIO13 for PWM. The calculator keyboard has 50 keys arranged approximately in a 5x10 fashion so that works out.

The only thing I'm not sure about yet is that for my power board I may need to use an additional GPIO for power control which means no backlight control. Another option is to multiplex the keyboard so that I can send voltage using only 3 GPIOs for the columns instead of 5 freeing up a pin. The downside is that it would require additional circuitry and I don't have much space inside the case.

I already modified the new display board. I successfully desoldered the 2x13 connector from the board and placed electrical tape over that spot so there wouldn't be any accidental shorts. I started modifying the case as well and was able to fit the audio connector right next to the display, which ended up being a bit of a challenge. I still need to enlarge the display window and cut out the HDMI port on the bottom. Once everything is done, if it turns out like I plan, there shouldn't be any issues placing the slide cover on the calculator.