The Case of the Wayward Elite-C

Split keyboard using Pro Micro controllers

Bad Pro Micro!

Pro Micro on the right with a sheared off Micro-USB port
USB port strength test of the Elite-C and Pro Micro

Different versions

Elite-C V1, so pretty
Elite-C V2 (pic grabbed from NovelKeys and then annotated)
Elite-C V3 with fancy castellated holes

Signs of trouble

How split keyboard detection works

Diagram of how power is shared between the two halves of a split keyboard

Rolling up my sleeves and digging into the issue

Testing rig (from left to right: Elite-C V3, Elite-C V2, 2 Pro Micros, Elite-C V3)

Logic Levels

Excerpt of ATmega32u4 Datasheet

Reading more datasheets

Top: Elite-C V2, Bottom: Elite-C V3 — Note that the Schottky diodes are different
B5817WL (Rated Peak Reverse Voltage is 20V, so 5V is 25% of that)
MBR1020VL

What do we do now?

Elite-C V3.1

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