geekhack Projects > Making Stuff Together!

Leyden Jar, tentative controller replacement for the Brand New Model F Keyboard

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suicidal_orange:
Good work, I love the rounded and irregularly spaced traces - reminds me of old school hand drawn PCBs :thumb:

Rico:
Thank you for your nice feedback!

Yes, some old PCBs had those organic traces: as they were hand drawn PCB designers could sometimes have a little bit of fun.

For the Leyden Jar some traces are rounded in order to limit signal reflection, not needed for the whole design but I found it would be nice looking to do that for all the traces.

Ellipse:
I had a question on the 16x8 matrix.  The beam 122 will likely have close to 128 keys (104/105 keys for standard ANSI/ISO + 12 F13-F24 keys + 10 keys for the left side block); close to the 128 maximum allowed on a 16x8 matrix. With this limitation, compromises will possibly be needed for those wanting to order custom layout 122-style beam spring keyboards, especially if they want additional keys like splitting the backspace, etc.

Would your updated controller design allow for an additional optional column or two?  It might be tricky with maintaining backwards compatibility (maybe a solder pad to switch it from being an extra column to being a ground column?  Or add it as a 34th pin if that is not possible).

Rico:
I have 2 IO pins still unused so I may be possible in the future to add one or two additional columns.
There are indeed a few ground pins that could be repurposed for that (thinking about the two in the middle of the connector).
This will need some PCB redesign though and lose compatibility as a result, but as I will probably find a few things to tune in the future, it could be for the Rev2 of the board.

I have yet to find time to check that the matrix scanning can work with this design, will take me a bit of time.
If it works well then:
- will need to check if the solenoid can work (unfortunately I don't have one on hand).
- will brainstorm the possibility of one or two additional column.
- make a rev 2 of the board.

Rico:
After a few weeks of holidays I am back on track to work on this project.
The goal is to now see if capacitive detection is working as well as on the LTSpice simulations.

Below is a test setup with one switch:



And the results I got were at first unexpected: not only it proved to work, but was working too well based on my initial expectations.
I could detect exactly the voltage value when no colum/row was connected, with the same value as the simulations.
But when a capacitor was wired the detected voltage level was out of the roof, so high that anything bigger than 0.5pF capacitance was out of my detectable voltage range (a maximun of 1V).
As I had only conducted serious LTSpice simulation on a full 16x8 switch matrix I told myself that I missed something for my understanding, so began to make simulations of a single switch.
… And I could obtain very close results compared to my initial test, great!

Also when adding columns in the mix the detected voltage level is getting lower and lower.
Let’s see what happens with a 5 colums and 5 rows matrix:



And I obtain very close results to my simulations of the same matrix with ~20pF of parasitic capacitance!

I am starting to think that having a working controller is now more a question of ‘when’ than a question of ‘if’  :)
To be 100% sure I have to write a full QMK firmware, let’s go!

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