49-key mini keypad

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This is/was the start of a clamshell - style calculator. A 49-key keypad, about 10cm x 6cm. Thanks to the Calculator origins, the artwork has suggested calculator functions for the keys.
The connector is PMOD-compatible, with and extra pin used to send interrupts back to the microcontroller. Schematics and PCB are in KICAD files at the Github.

There are other mini keyboards around: fully functional, bluetooth connection, and cost less than what I'm charged for SMD switches [let alone diodes, board, controller chip, case, keycaps etc]. But maybe the design can be used as a stating point for YOUR design...
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  • 49 × 1N4148 SMD Diode Discrete Semiconductors / Diodes and Rectifiers
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  • 2 × 10K Resistor SMD Resistor
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Jan Szumiec wrote 10/04/2016 at 20:26 point

Hey, I'm building something simliar. What do you need the diodes for in this design?

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alan_r_cam wrote 10/05/2016 at 09:50 point

n-key rollover is a problem when you press multiple keys (control-alt-delete). Theres some great write ups in the Reddit groups on mechanical keyboards. The fix is the diodes.

If you never expect to be pressing multiple buttons at once, you could leave them out. Your choice

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Jan Szumiec wrote 10/05/2016 at 10:02 point

Thanks, this is very useful info.

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alan_r_cam wrote 03/12/2014 at 02:52 point
My original plan was to mate this with a 4.3" LCD, a battery, and an ARM microcontroller. However, my first batch of PCB's have already cost more than the eBay price of a mini Bluetooth wireless keypad. This has severely impacted my desire to continue with the design.
Common sense tells me I should just use a existing keypad, coupled with an iPhone or Android. What do you think?

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Rocko wrote 03/29/2021 at 23:12 point

Your original plan is way cooler.  It may cost more but, you will get more out of it I think.  Also, one of anything you design will always cost more than one of anything on eBay.

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