So I am working on a school project where I am making a "Smart" Geocache. Basically, you solve a puzzle of some sorts and the lock opens up. Instead of doing a typical puzzle though, I want to make it so that when you complete a game, the lock opens up. I was planning on using my TI-84 Plus CE as the screen and connecting it to an arduino. Then programming a game (2d platformer probably) on it and setting it up so that when a person wins the lock opens. The only thing I have no clue how to do is connecting the arduino to the calculator. Can someone guide me on how to do that? And if it is not possible, then can someone please help me by recommending me options on buying a colored LCD (or some type of raspberry pi kit) that can connect to an arduino and can have some type of platformer game coded on it? I will obviously code the game myself.

Thank you for your recommendations.

I'm not sure that a CE can be programmed with an arduino. If you had a TI-84+, you could do articl, but I don't think it's possible to do it with a CE yet. Of course, you could also write a extension to articl for use with the CE.

Unfortunately, I can't help you with buying a LCD, but good luck.

What kind of resolution and size do you want? 320x240 (the same as the calc?).

Do you have to use an Arduino/uC? It is possible to program the calculator directly with C these days, which is pretty straight-forward and comparable to programming on the Arduino as well.

If you must use a uC then I would recommend an SPI LCD of a reasonable size that you can get off eBay for cheap. There are a lot that are Arduino compatible such as: https://www.adafruit.com/product/1480 and like I said much more affordable ones on eBay:

http://www.ebay.com/itm/Pro-TFT-2-8-240x320-ILI9341-5V-3-3V-SPI-LCD-Serial-Port-Module-PBC-Adapter-/401383987173?hash=item5d745997e5:g:T34AAOSw8GtZPqa2
http://www.ebay.com/itm/2-8-240x320-SPI-TFT-LCD-Serial-Port-64K-Module-w-PCB-Adapter-ILI9341-5-3-3V-SG-/112484795736?hash=item1a309dc558:g:Iz0AAOSwb~9ZbGZ7

Arduino tutorial for display: http://www.instructables.com/id/Cheap-TFT-22-inch-Display-on-Arduino-ILI9340C-or-I/

Adafruit library: https://github.com/adafruit/Adafruit_ILI9341

Will work with Raspberry Pi with minimal fiddling as well via FB-TFT.

I know I can program directly onto a calculator but the problem is I have no clue how to open the lock once the player has won the game without an arduino of some kind. Is it possible to open a lock with only a calculator? Also, does the SPI lcd connect to the Arduino Nano because I have to use that version of Arduino?

Thank you for helping me.

Well with the CE it isn't currently well understood how to interface with USB, though there are a number of people who have had success with experiments (jacobly?).

The Arduino Nano does support such SPI lcd's I believe.

Here is a youtube test with a similar looking LCD as to what I linked earlier: https://www.youtube.com/watch?v=1C5PAzAi6oE

EDIT - That being said, you CAN interface with external hardware much more easily with older calculators. The TI-83 right through to the CSE have a standard 2.5mm linkport that many people over the years have utilised to do just that.

Okay thank you for the input. I just thought of something that might allow me to not use the arduino. If my teacher allows me to buy a physical lock with a combination, I can simply make it so that once the player wins the game, the combination is outputted on the calculator screen. If my teacher doesn't allow that then I will either just buy the lcd you recommended or get a calculator with a 2.5 mm link port. I think I will just do the lcd option if my teacher makes me use an arduino (since it is cheaper than buying a new calculator).

Again, thank you for your response, it definitely helped me make my decision.

No Problem - Also these LCD's are pretty simple to get working on something like a Raspberry Pi as well.

If you are thinking about the calculator route, go for a 2nd hand one off ebay - you can usually get them very cheap.

Someone here might have an old one they can sell to you as well.

Well, there's the TI-Innovator Hub.
It's comparable to the Arduino but made specifically for the TI-84+CE.

You plug the calculator into its USB port and then you can write TI-BASIC code to control it, and it has IO pins like an Arduino or Raspberry Pi. It would be able to do what you want, assuming you don't mind buying another device. They aren't cheap.

Update on the project so far. I am pretty much done now, I just need to paint the cache and fix one "minor" problem.
Here is a demo of the front portion of the cache in action:
http://youtu.be/Zrc5LeqOwkc

The front portion will be placed in a bird house to hide it from the public eye.
http://imgur.com/a/mE6Zn

The best way to describe the actual game is that it is a Flappy Bird clone however, the holes get smaller over time and you get faster. In order to get the combination to open the lock you must first solve this riddle:

In 1949 he made,
A book within a future decade,
Remove the first two from the title,
To gain information that is vital,
Make sure around there is no other,
Or you'll be caught by Big Brother.

Once you solve it for a number you will have to play the game until you get to that number then you must make yourself lose before you pass that number. Then you receive the combination for the lock.

The only problem so far is that the button hurts your finger and I am not sure how to fix that yet.
I wanted this project to be much bigger but due to time constraints I had to reduce it too much less...