3/16/2026 1:04 AM - Researched Calculator Parts- March 4

Since I first thought of this project, I've spent around 6 hours learning about how calculators work. They basically have PCBs inside that have a set of intertwined pads for each button. Then there's a rubber pad with conductive spots and when you press down, it recognizes the press. I'm thinking about making a similar PCB to connect to a Raspi Pico!

I spent a lot of time just researching calculators and thinking about which one I want to modify!

Here's a look at an example internal image:

Source: https://www.ifixit.com/Guide/Repairing+Buttons+on+Casio+fx-300ES+Calculator

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

Remember, follow the order of the journal entries except for the ones that say retrospect entry!

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).

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!

3/31/2026 1 AM - Schematic and Firmware are Finalized!

One day before Blueprint ends and I just finalized the firmware for the Pico and created my schematic. I'll add it to my Github on the final day, as well as my entire README and BOM! It's been about ten hours of work over the last two weeks since my last journal (remember I am new to this software so a lot of this project is spent learning!)

This is my schematic as of now. BOM is basically done and ready, budget is excellent, now I just need to make a very detailed explanation on why I chose the parts and how it works, the features and how one can make it themselves step by step.

3/31/2026 10 PM - Schematic OVERHALL

Just over an hour left, and I'm remaking the schematic to be more organized. I've sort of figured out what to do, I may need to update my repo a little bit after I submit, but I think I'm good to submit for project review that way I don't miss the deadline!

4/1/2026 1 AM - Final Entry Until Building!

BOM is up to date!

A note to reviewers:
I submitted this project as tier 2 when it absolutely doesn't qualify for tier 2. This is a tier 3 project at max according to the tier docs, meaning the limit is 100 USD.

When submitting I panicked and put tier 2 because my total was $117.16 CAD. The amounts I requested were incorrect, it's worth $84.23 USD meaning it fits within Tier 3.

To summarize:
TIER 3- $84.23

4/1/2026 10 PM - UPDATED BOM TO INCLUDE SHIPPING COST INCREASE

A note to reviewers:
I submitted this project as tier 2 when it absolutely doesn't qualify for tier 2. This is a tier 3 project at max according to the tier docs, meaning the limit is 100 USD.

When submitting I panicked and put tier 2 because my total was $117.16 CAD. The amounts I requested were incorrect, it's worth $84.23 USD meaning it fits within Tier 3.

NOW THE PRICES HAS GONE UP TO $94.48 USD because of shipping fees

To summarize:
TIER 3- $94.48

4/4/2026 2 AM - Updated BOM!

I just updated my BOM to include the latest costs. I also tried to find some cheaper options to get shipping down. It ended up being very similar to the original cost. It totals to $93.05

I spent like 2 hours looking on AliExpress and I DESERVE those hours 😭😭

4/4/2026 3:10 AM - March 5- Retrospect Entry- Chose Calculator

So far, I chose the calculator I wanted to modify (Casio FX-991ESPLUS2), and ordered it on Amazon.

I spent a while choosing this, because I wanted to ensure the parts fit together properly inside this casing.

The calculator have been ordered and will not be part of the grant request (it would be well over the budget of the tier that this belongs in).

4/4/2026 3:18 AM - March 6- Retrospect Entry

I'm going to use a Raspberry Pi Zero 2W and a Pico 2 (both are faster and more power efficient than their predecessors).

The Raspberry Pi will be the main brain that displays to the screen and the Pico will be the input controller that's hooked up to my custom PCB which will be using matrix scanning (see the entry from the 16 of March).

It will be able to run any Raspi OS meaning I can program it to do whatever I want within Linux
This opens up a RANGE of possibilities!

4/4/2026 3:20 AM - March 7- Retrospect Entry- Calculator Arrived

THE CALCULATOR CAMEEEE!!!
I 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.

I will now hollow out the back side!

4/4/2026 3:23 AM - March 8- Retrospect Entry- Hollowing Back!

This is the current state of the calculator! I used a mechanical sander to hollow it out since I didn't have a dremel

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 picture sorta goes with the last entry but I don't have a pre sanded gutted image so I put it like this. Regardless, the hollowing took a long time with the sander!

4/4/2026 3:27 AM - March 10- Retrospect Entry- Finalized Screen Choice

I measured the space I had in the calculator shell and ordered the screen from AliExpress!
The bigger screen has touchscreen which will be super useful for navigating the UI!

As of now those are the only things that have been ordered!

I also ordered a backup, slightly smaller screen just incase.

These, nor the calculator will count towards my grant.

I wanted the best screen for the job and I genuinely spent so long on this. It was probably around 9-10 hours of research looking back on it. It was spread out over March 9 and 10, because according to my AliExpress history I ordered on the 10th.