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monic part 3: towards a handheld
07-01-2020, 01:54 AM (This post was last modified: 12-09-2020 01:41 AM by F-73P.)
Post: #1
monic part 3: towards a handheld
Previous: monic part 2: connecting the keypad

I will now place the display and matrix keypad on veroboard. The calculator can then be connected to a development board (such as the NXP i.MX RT1010 I have been using so far) via terminal blocks on the left of the veroboard.

I am also trying to find keycaps for the Omron B3F-1052 pushbuttons; any suggestions?
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07-01-2020, 10:17 AM
Post: #2
RE: monic part 3: towards a handheld
Hello!

Very interesting project, looking forward to see more of it.

(07-01-2020 01:54 AM)F-73P Wrote:  I am also trying to find keycaps for the Omron B3F-1052 pushbuttons; any suggestions?

I have used this kind for some tinkering projects in the past (this is an eBay-link, unfortunately I couldn't find them anywhere else - they come from China anyway, no matter who you order them from):

https://www.ebay.com/itm/A14-Tactile-Cap...3216076402

You can select a keycap in the colour you like and snap a transparent cover over it. The gap between keycap and cover is large enough for a key label printed on solid/thick paper. These caps should also fit your Omron switches, but better compare the measurements.

Regards
Max

NB: Maybe I missed it in your earlier posts, but what does "monic" stand for?
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07-23-2020, 04:02 AM
Post: #3
RE: monic part 3: towards a handheld
(07-01-2020 01:54 AM)F-73P Wrote:  I am also trying to find keycaps for the Omron B3F-1052 pushbuttons; any suggestions?

We use them in a couple of our products at work. Availability has never been a problem at all. See https://www.mouser.com/Electromechanical...ps&FS=True

http://WilsonMinesCo.com (Lots of HP-41 links at the bottom of the links page, http://wilsonminesco.com/links.html )
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07-28-2020, 09:21 PM (This post was last modified: 07-28-2020 09:25 PM by Chr Yoko.)
Post: #4
RE: monic part 3: towards a handheld
Very nice project !
Your chosen microcontroller looks very powerfull , why such choice instead of a 32bits Arduino such as a STM32 base ?

Hereby EEVblog that is showing how to get made a custom membrane keyboard :
https://www.youtube.com/watch?v=H8XBBfvsPj0
From here :
https://www.jrpanel.com/switch/buy/
(exemple @ about US$255 for 4 parts, with embossed keys , their stainless domes and 4 colors on the overlay)

[Image: JRPanel-Membrane_switch-Graphic_overlay.gif]

OK, bit expensive and not as good as a real keyboard, but has a professionnal look to it.

Also I would be interrested by the software side of your project ;-)
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08-01-2020, 05:58 AM (This post was last modified: 10-26-2021 06:03 AM by F-73P.)
Post: #5
RE: monic part 3: towards a handheld
Thanks for the suggestions. I've ordered Japanese "Alps Alpine" switches and keycaps, and have started making some keypad labels.

(07-28-2020 09:21 PM)Chr Yoko Wrote:  Also I would be interrested by the software side of your project ;-)

See here for firmware for a programmable scientific calculator.

After the handheld is built I will focus on adding support for arbitrary-precision rational and floating-point arithmetic.

(07-28-2020 09:21 PM)Chr Yoko Wrote:  Your chosen microcontroller looks very powerfull , why such choice instead of a 32bits Arduino such as a STM32 base ?

The i.MX RT EVK boards offer speed and large memories, and the IDE is free and supports programming in C and assembly.

(07-28-2020 09:21 PM)Chr Yoko Wrote:  Hereby EEVblog that is showing how to get made a custom membrane keyboard :
https://www.youtube.com/watch?v=H8XBBfvsPj0
From here :
https://www.jrpanel.com/switch/buy/
(exemple @ about US$255 for 4 parts, with embossed keys , their stainless domes and 4 colors on the overlay)
OK, bit expensive and not as good as a real keyboard, but has a professionnal look to it.

Thanks for the links, they look great. Definitely something to keep in mind for the future.
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10-25-2021, 08:27 AM (This post was last modified: 10-28-2021 05:14 AM by F-73P.)
Post: #6
RE: monic part 3: towards a handheld
Handheld prototype 1.0 is finished.

Schematics:

[Image: 51627501993_b24c5157b7.jpg] [Image: 51627498483_977a38f56d.jpg]

Soldering the wires, buttons and connectors to the veroboard:

[Image: 51628135605_ef23e914a9.jpg] [Image: 51627500763_6f9280068e.jpg]

Attaching the display and spacers:

[Image: 51626448627_773134aa32.jpg] [Image: 51627275056_d060b9aae6.jpg]

Connecting the microcontroller:

[Image: 51627497843_d4818b3b6d.jpg] [Image: 51628131460_8b227065f0.jpg]

The shift functions:

[Image: 51627495098_245fe91d21.jpg]

The final result:

[Image: 51626443852_cc1801b291_b.jpg]

Next: monic part 4: arbitrary-precision rational arithmetic
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