I usually prefer to design my models for printing using OpenSCAD and the TLT was no exception! I did end up regretting this slightly as I had a need for faster iteration than usual.

I wanted to start this project with the case so I had something tangible to work on and motivate me. The basic design I chose is based around the mounting posts on the back of the touchscreen module and two plates that lock into the top of the simple box case. Even though the name of the project includes `tablet` I was not concerned with making the case thin or light. I wanted to make it sturdy and easy to mount, for more of a hands-off use case, so I included an aluminum camera cheese plate with plenty of options for threaded mounts. Additionally, the battery is external and mounted using a camera v-mount. This allows for easy battery swaps and the ability to use a larger battery or no battery if needed. I imagine that a Power over Ethernet solution would be ideal for a permanent installation in a manufacturing environment but I do not have the proper equipment to test/design the case around that.

The dimensions of the case are based around the measurements of the screen module and Raspberry Pi assembly. The screen assembly is mounted to a mid-plate that holds it close to the face of the case body and aligns the screen's panel with the centre of the tablet. The mid-plate is mounted to the case body using 2x M3 screws with heat-set inserts and two tabs that interlock with pockets on the top side of the case body. The final case part is a lid that uses a similar interlocking tab design to lock into the top of the case body but with one tab that spans most of the tablet's width. The lid is secured using another 2x M3 screws with heat-set inserts and supported by some rails along the sides of the case body. The lid is designed to be easily removable so that the screen assembly can be removed from the case body for maintenance or repair. Originally I wanted to include easy access to the GPIO of the Pi but I was running into difficulties with iterating the design quickly and decided to remove it from the scope of the project for now. I was thinking a lid shape that allows for the GPIO to poke through or use an extender to allow for more flexible positioning. The cheese plate and battery is on the lid, simply bolted on using some through holes.

The button area of the tablet is centred to the screen and with the 7 inch screen chosen, there was exactly enough room for eight switches using standard MX key switch spacing. This works out nicely for the software key map display that will appear along the bottom of the screen. As I worked on the case and printed some prototypes, I saw the need for more of a modular approach to the button area and in the future I plan on separating the button area into a modular part that can be mounted to the case body. This would allow for different button layouts and sizes to be used with the same case body with the possibility of using other inputs like rotary encoders.

These parts were designed for 3D printing so I have tried to reduce the need for supports. I didn't mind the plain aesthetic of the case but I did want to add some visual interest to the design and make it more comfortable to hold so I decided to add some fillets to the edges and corners of the case. I am currently on my third printed revision of the case and I am happy with the results so far. I have included the OpenSCAD files for the case in the repository and I will continue to update them as I make changes.