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A comment on Apple iPod Shuffle USB interface pinout. Parent comment

Re:Apple iPod Shuffle USB interface pinout by rollcat on Monday February 05, 2024 @03:41AM (#39258725)
USB is usually too complex for something like a simple split keyboard; the TRRS runs I2C with sth like a MCP23018-E/SP IO expander in the other half.
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Re:Apple iPod Shuffle USB interface pinout by adolph on Monday February 05, 2024 @10:26AM (#39262175)
You can use a physical connector without using the standard protocol.
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Re:Apple iPod Shuffle USB interface pinout by crote on Monday February 05, 2024 @01:05PM (#39264422)
Most split keyboards these days have a microcontroller in each half. IO expanders like the MCP23017/MCP23018 are fairly expensive, quite slow when used with microcontrollers like the ever-popular Pro Micro's ATmega32u4, and they really limit your hardware options on the secondary side.

It usually makes more sense to just stick a Pro Micro on each side, and have them talk serial over TRRS. As a bonus, you can connect it to your PC from either half.

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