3/16/2026 1:04 AM - Chose Calculator I wanted to Modify

Since I first thought of this project, I've spent around 40 hours learning about how calculators work, which one would be best here, and what components I would need. I didn't add to the journal when I started my research, so I just put 40 hours which is my estimate of how long I've spent so far, and this entry is my starting point on Blueprint!

So far, I chose the calculator I wanted to modify (Casio FX-991ESPLUS2), ordered it on Amazon and opened up the insides of it!

I completely gutted the internals, removing the LCD screen, solar panel, battery and any wires.

I removed the PCB that came with it and also removed the rubber pad with conductive points on it that goes over the buttons! This space made room for my custom internals. I chose to start with the original calculator shell to make it as similar as possible to the original, rather than 3D modelling a new one.

Here you can clearly see all the internals visible (the buttons are in a safe bag separate from the rest of the stuff so I don't lose them). I then sanded down the plastic on the back shell to make even more space (it was just plastic pushing against the PCB to hold it in place).

This is the current state of the calculator!

After doing this, I measured the space I had and ordered the screen from AliExpress!
As of now those are the only things that have been ordered!

I will update my Github Repo with as the project is further designed! Please see my Bill of Materials as it changes!

3/16/2026 1:40 AM - Routed the PCB

Remember, just because my other journal was published like 30 minutes before this one, I still really did spend 10 hours on this, the first journal entry was just published late!

Now onto the actual entry:
I just spent a long time learning how to use EasyEDA and route PCBs. I think I got the hang of it now!, I'm going to wait for the screen to arrive from AliExpress to get a sense of the sizing of where I want the solder points on the PCB to be located, before I actually order it. Since no one has done this before, I have to order parts piece by piece based on size.

Here's the PCB so far that I spent 10 hours routing:

Top View:

Bottom View:

The PCB is simply made to be a replacement to keep the original feel of the calculator, but letting me hook it up to the Raspberry Pi! I am thinking of just using a Pico connected to the PCB and connect the Pico to the Raspi Zero 2 W! Calculators work by having the button press on a rubber pad that has a conductive surface, which completes the circuit on the PCB for that button and tells it what you pressed. My PCB has sets of pads with fingers to allow for the maximum contact ability. An ENIG finish is going to be required so that the exposed pads don't lose their ability to recognize the button press after oxidization!

It's wired with the left side in rows and the right sides in columns on the other side, and each row and column is connected to the Pico. It then uses matrix scanning to tell what button is pressed (Ex. pad in Row 8 and column 2 is the number 2, same with all the other functions and numbers).

In the meantime, I'm going to set up my repo since I haven't done that yet! I'll get started on my README, and start on the code since I want the Raspberry Pi in the calculator to constantly pull updates from my Github whenever I push changes, for easy, headless updates that are all visible to people looking at my project! This keeps my code transparent and any changes I make visible!
I'm also going to add a bill of materials as it is right now, as well my current PCB files and images!

3/16/2026 2 AM - Published my GitHub Page!

Github repo has been created, I just added all the files and folders I would need, the only real code is the Pi's auto Github pull code to pull my changes automatically every once and a while (if I'm doing serious debugging I'll remotely connect through VSCODE).

Raspberry Pis have been ordered from Amazon (surprisingly cheaper than AliExpress)!

BOM will be added tomorrow, as it's late.

Here's a final look for the night:

3/20/2026 2 AM - Screen Arrived!

The screen arrived 2 days ago but I have been very busy so I didn't get around to writing this journal entry. I tested the screen on this Raspi 4 I had and it seems to work just fine! It is a little big though so I might need to shave down the PCB that doesn't have any traces on it.

Don't mind the scratches it's just on the plastic cover. I'm going to put together the BOM now and get all the code working, so it can run on the Pis when they arrive.

3/20/2026 3 AM - Code Prototype Done!

I've been writing the code recently too, spent probably around 3.5 hours on it, writing this journal just now so the times aren't accurate. The code is in a prototype state, anything is subject to change if something doesn't work as I planned online, since I don't have the Pis yet. Troubleshooting is going to obviously happen but I'll adjust the code as needed to fix future issues that I have.

I'm now going to work on the BOM tomorrow morning, and make a full detailed README. Right now I will attach screenshots and PCB files of the final design. Other than that, the project is ready to submit!