Author Topic: Das Keyboard Matrix Observation  (Read 1328 times)

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Offline StrikeEagleCC

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Das Keyboard Matrix Observation
« on: Sun, 01 September 2013, 10:42:41 »
I've learned a lot about keyboard design and functionality in the last week and admired many of the fantastic builds here. Comparing them to my first mechanical keyboard (Das Keyboard Pro) has raised some questions for me.

First, the matrix of my Das is 8x18, which seems excessive for a 105 key board. Several columns have only modifier keys on them. The PCB routing is excessively complicated. The only justification I can figure is that the PCB was designed to accommodate a keyboard without diodes while minimizing ghosting. However, the installed diodes are necessary for matrix completion, and assembly without them would have to substitute jumpers for the diodes. From a manufacturing perspective, this might save $2 in part cost, and $0 in assembly cost, and that's being generous. What would be the point of omitting them? Does Das Keyboard even have a product like this, or do they have another re-branded line of products?

Also, the diodes' cathodes are connected to the columns, which now I understand means that the columns are being driven low by the controller one at a time while the rows are monitored. Looking at some of the projects in the TMK firmware, I see that some keyboards have the columns driven while some drive the rows instead. Is there an advantage to either approach?

Lastly, why are pins configured with pull-up resistors and then driven low, as opposed to keeping all pins low and driving them high?
A better example of how your keyboard works:
More
It's expandable and ~25 seconds long.