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Yet another DIY RPN calculator
05-28-2021, 08:48 PM (This post was last modified: 05-30-2021 03:00 AM by Gene.)
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Yet another DIY RPN calculator
Hi all,

I've been reading this forum for quite a long time, but did not bother to register until recently. I've used RPM calculators back in school, mostly to fly to the Moon, then I've switched to algebraic ones, then I didn't own any hardware calculators: was either using a Python prompt or cell phone apps.

Recently it occurred to me that I needed a hardware calculator. Not that I desperately needed one, but it would just have been convenient to have something lying on a table which I could use for some back-of-the-envelope style estimates, without the need to start apps, open terminals, etc. Ideally, it would need to have some specific functions that I often need (I'm doing high-energy physics).

I hate to admit this on this forum, but I don't see a use case for programmable calculator for me. If I need to program something relatively complicated, I'd better do it on a computer. Instead, I'd like to have a set of rather specific functions which would only be one-two clicks away (of course I could have programmed them on DM42 or whatever, but running a program is by far not equivalent to pressing a button).

Thankfully, modern MCUs make building custom calculators relatively easy. So I ended up make my own one (I'll resist citing Futurama here). Here's what comes out so far:

[Image: calc_stickers_face.jpg]

The design is kind of inspired by DM42, at least it's using the same Sharp LCD and STM32L476 (good choice, SwissMicros!). The schematics is of course much simpler, as I did not intend to implement any fancy stuff. I've tried to make the keyboard as soft as possible by using 50g actuation force switches. The case and keypad are 3D printed, and key labels are made using laser printable sticky film.

Firmware-wise, it is of course in a constant development. but I think now it largely has most of what I wanted to have in my custom calculator. One notable feature which I think was not implemented in any hardware calcs so far is calculations with uncertainties using error propagation.

I'm publishing all the design files in github under free license, hopefully it could be useful for somebody to make their own machine.
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Messages In This Thread
Yet another DIY RPN calculator - apoluekt - 05-28-2021 08:48 PM
RE: Yet another DIY RPM calculator - ttw - 05-29-2021, 07:48 PM
RE: Yet another DIY RPN calculator - mpark - 05-30-2021, 05:57 AM
RE: Yet another DIY RPN calculator - tcab - 05-30-2021, 07:50 AM
RE: Yet another DIY RPN calculator - tcab - 05-31-2021, 12:21 AM
RE: Yet another DIY RPN calculator - Ren - 05-31-2021, 04:10 AM
RE: Yet another DIY RPN calculator - rawi - 05-31-2021, 04:47 AM
RE: Yet another DIY RPN calculator - rawi - 06-01-2021, 07:19 PM
RE: Yet another DIY RPN calculator - Gene - 06-05-2021, 07:49 PM
RE: Yet another DIY RPN calculator - Ren - 06-05-2021, 10:30 PM

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