Hi,

I've been set a test project by a potential employer to convert a simple calculator such as a CASIO FX-82ES so that it has the capabilities of a scientific graphing calculator such as a TI-83. The rules of the project are that I can change anything about the simple calculator (e.g processor, screen etc) however on a quick inspection it must look like there has been no modifications.

I would appreciate some advice in how to approach this problem.

I was thinking of running a Ti-83 ROM on a Rasperry Pi Zero type device. Would it be possible to connect the buttons from the simple casio calculator to the GPIO on a Rasperry Pi and accept them as input? I'm concerned how I would manage to map these buttons successfully to the Ti software. And then would it be possible to output that to the more primitive screen of the casio?

Ultimately I'm not sure what resources in the simple calculator could be reused and what would have to be replaced to allow for the more advanced functionality of the Ti software.

Any help would be greatly appreciated , I have found somewhat similar calculator projects to this online but none of them regarding the conversion of the simple to scientific.

A test project from a potential employer? Are they actually expecting you to do weeks of work to get a job?

I would say scrap everything and just use the case. Get the thickest "simple calculator" you can and then put all of your own electronics in it. That way you don't have to worry about reusing existing electronics and potentially misunderstanding them. I wish I had not used the original keypad when making my Gameulator which seems to be a similar concept to what you are trying to do. As for what actually goes inside, whatever you really want. That's the beauty of not having to work with what's inside already!

If the keys are actually individual push buttons instead of just conductive rubber on the pcb, then probably don't scrap them. To use them effectively though, you might want to use the input mode of a shift register to save pins on the GPIO of your RPi. I have little experience you could on using external non-usb hardware as a keyboard, but you could probably just write a python script with some keypress-simulation-library. You could use this emulator, with both of them launched on startup. I have no bearings on any recommendations to give you for a screen.

But what kind of job would have this test project?

I am not an expert on this but this kind of test seems odd.

Have you considered asking on: https://workplace.stackexchange.com/ if this is right?

I'll be honest, this sounds like a cheating method on tests that don't allow the use of graphing calculators.

edit:
For a serious answer, it might work by building a raspberry pi zero, a screen, and a small powerbank into the casing of a thicker, older calculator. I don't know how you would connect to the keyboard though. Maybe you'd need to print your own keyboard pcb [see img], and connect something like a makeymakey to it? Maybe directly to an arduino/raspberry if that's possible?

I wouldn't know how you would fit that into a package like that though.