Screen size is insufficient for HP50G or DB48x/DB50x

[c3d]

Hi @xavierbasc, great initiative! I look forward to having a cheap, custom, open-source platform to run DB50x on ;-)

On the front-page, you list two things that make your intent a little bit unclear:

• Graphic LCD Display (128x64 dots).
• A list of software used in calculators that includes DB48x, C47 or WP43

This makes the goal of your hardware project a little unclear. If you want to run the original HP ROMs through some kind of Saturn emulator, in the same vein as the HP50G did, then the resolution is close, but insufficient. The HP48 did indeed have 64 pixels vertically, but it was 131 horizontally (don't ask). So 128 means you lose 3 pixels. The HP50G, on the other hand, had 80 pixels vertically, so this makes things even worse. Finally, the SwissMicros devices settled for a high-contrast black and white 400x240 pixel screen.

There is a variety of displays available on the market. Have you already settled specifically on this 128x64 for any particular reason, or is this something that could be more open in the design?

Here are some options I can think of:

1. High-resolution e-ink like SwissMicros. Pros: porting the existing firmware is easy. Cons: Not direct multiples of the HP resolutions, so upscaling if you want to emulate ROMs may look a bit strange. However, note that the DM42 display is very close to 3x upscaling compared to the HP50g. There would be only a very small number of pixels lost.
2. High-resolution color display: Pros: could take advantage of the color support in DB50x. Can be seen in the dark. See usage of color in HP Prime. Cons: cost, power usage
3. High-resolution color e-ink: Does that even exist? I've seen 6-color displays, but nothing with a high-enough resolution. Did not look in a long time.

[xavierbasc]

I was considering different types of screens, including e-ink displays, but the issue with them is that there are no screens of a similar size (65-70mm) with the connector (especially this one) located at the top or bottom. All the ones I found (and I searched a lot) had the connector on the side, which adds unused space to the side of the calculator, making it look frankly bad.

I also want to thank c3d for the helpful comments and insights.