We just wrapped up the NeoKey Trinkey tester, which uses a Teensy to program the SAMD21 processor and then test the USB interface. It's a simple USB A pluggy-board with a cherry MX-compatible footprint (can use Kailh, Gateron etc!) with underlit NeoPixel and one capacitive touch pad. Simple and fun, its your new best friend! Great for adding ESC keys to old macbooks.
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