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Meeting Notes (2020 08 18)

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Alex McLain edited this page Aug 19, 2020 · 5 revisions

Meeting Notes

  • KiCad / PCB layout
    • Trying to lay out a naive 8x9 matrix on the PCB doesn't work well because the keys aren't physically arranged the way the matrix is wired.
    • The physical matrix is more like 16x5. Electrically 8x10 if you split the rows down the center and duplicate the columns.
    • We probably aren't going to be happy with an off-the-shelf key scan IC because they don't meet all of our specs (scan rate, max keys detected simultaneously, too small - difficult to prototype with).
    • We probably want to roll our own key scan solution. The BeagleBone Black PRUs look feasible. An FPGA is an alternative.
      • If we do this, we can drive/sense the rows/columns however we want.
    • It doesn't matter where the rows and columns physically connect, as long as they're electrically connected.
    • We need to overlay 2 matrices: The keyboard matrix + the LED matrix.
    • LED matrix
      • We would need to use two of the IS31FL3733 matrix drivers.
      • Rather than using the second IC to drive the leftover LEDs after maxing out the first IC, each IC could drive half of the LEDs.
        • This may also let us reuse a lot of the existing matrix if we add more keys/LEDs.
      • We could put the ICs on the back of the keyboard for the finished product.
    • Processor
      • May need to use a pin header or flat flex cable that allows us to put the system processor on a separate board to avoid interfering with the keys.
      • Or make a space at the top of the keyboard for the controller.
  • LEDs
    • The RGB LEDs can consume 20-30mA of current.
      • This would be about 4 amps for all of the LEDs at full brightness.
      • This would exceed the USB 2.0 current limit.
      • We could put an artificial limit on the brightness to reduce current consumption. To the user it's 0-100% brightness, but we set in hardware what the max brightness value we send to the LED matrix drivers.
    • The Keybow uses APA102 LEDs.
      • They're probably too small to hand-solder (hand-reflow).
      • They work by chaining them together and shifting serial data through the chain. Not great for prototyping because we have to populate them in the order they're wired together if we only want to test a few of them on the board to start out.
    • Wurth 150352M173300 LEDs should be compatible with the ISSI driver IC.
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