I am developing a 6-function calculator (+,-,*,/,%,sqrt) with a 144x32 dot-matrix display.

Since I have chosen a dot-matrix display for such a "simple" thing, it only makes sense to implement more features into the calc to make it more accessible and user-friendly! So far I have already come up with a "status line" layout like this:

The top left is your bog-standard "memory" indicator that shows if you have a variable stored or not. The top right shows the battery percentage/voltage, depending on if you're running the calc on rechargeable/disposable batteries, respectively. (This is necessary due to the backlight in the LCD, as well as some planned features like communication with PCs over UART and full C/ASM re-programmability.)

So my question is, considering the average run-of-the-mill $2 4-function, what features would you like to see on a basic calc to enhance its usability?

I'll start: I would love to see a feature allowing you to view the contents of your memory variable without actually having to paste it into your entry line.

(Note: I will not accept suggestions that require adding more mathematical functionality to the calc itself. The objective here is to design the 'ultimate 6-function'.)

P.S. I can guarantee that the final product (and most likely its development as well) will be completely open-source.

Isn't that 6 functions? (joke)

I like the idea, I think being able to lookup calculation history would be handy.

Dark mode, light mode, and brightness? You might have already put that, but just saying. Also, maybe a color palette customizer or something like that, to change theme colors and that kind of thing.

Having a ton of precision would be cool, although that would require left and rigjht arrow keys.

Dark mode will be “on by default” as the LCD i linked to is actually built in such a way that the background itself is black and the pixels are white when “on.” I suppose it wouldn’t be too difficult to program an ‘inverted’ mode where it’s all in light mode.

The backlight definitely supports setting specific levels of brightness, so perhaps I could add a rocker-type of control on the left side of the calc like an iPhone volume button to control brightness.

Unfortunately the LCD does not support color. However according to the data sheet it has at least a 200ms response time meaning that grayscale should be easily possible.

Noted, thank you. This should be done to a microSD card perhaps, since QSPI PSRAM will be quite limited when doing high-precision calculations.

Though I believe this would require the introduction of a D-pad. (Is that a problem? I think it may make the physical appearance more complicated than needed, but idk of any other user-friendly input methods to make the scrolling through history happen.)

A few questions:
1. How much memory is at your disposal?
B. Is the % a percent or modulus function?
7e. Can it do decimals/fractions?
ζ. Can it run Doom?

Just spitballin' here, and I don't know if this is feasible given the limits, but if you don't want to add extra keys, you could repurpose the On key or something as a 2nd or shift key. Then you could use the numbers as a d-pad.

1. Looks to me like 16MB or 32MB (if we’re lucky) is possible on the RP2350, the chip that is going to be at the heart of this thing. Also, this thing has programmable I/O state machines independent of the main CPU cores, so some of those will be used to interface with a mSD card SPI-style.

B. % means literally a %.

7e. Ehh, I doubt adding support for rational fractions keeps it a four-function. Most standard 4-funcs can’t do fractions directly. But I suppose in general it should be acceptable to implement fractions.

ζ. Only if you know how to get the calc to run custom firmware, which will be freely documented.

This sounds awesome! How about adding a history feature to scroll through past calculations or a quick undo for mistakes? A toggle for degrees and radians would also be handy. Love the open-source idea—can't wait to see it!

History is probably going to be possible via microSD cards, since main RAM will be full of numbers due the calculator’s high-precision nature.

Degree and radian toggling only matters when doing trig functions, right? I don’t think it would matter on a 4-function, since it can’t do trig…

Maybe add the ability to add key shortcuts? Like if you wanted to view your exact battery percentage, the amount of calculations you have stored, or your brightness/volume levels, by pressing a key like * and - or something like that.

Has this project been paused?

Yes. I am currently working on some stuff for TI-68k calculators as it’s just more fun for me at the moment. I promise I will get back to this within the next year though.

A data-out for possible expansions would be nice, for perhaps a printer or using an Arduino to log expressions or something. Nothing fancy, just outputting whatever numbers are being used during a calculation in binary with a clock line to keep in time.

The MCU I’m planning to use will be quite beefy (16+ MB RAM), so it will be very easy to use a standardized protocol like UART for that too.

Theoretically one would be able to type things in the UART console and those changes would be reflected on the physical calc screen, and vice versa. Same for the calc displaying things after finishing computations. I’ve actually gotten the code infrastructure around such an idea mostly implemented.

Would that work as well?

I don't know enough about UART to know but I would imagine it would work alright.