Pro Micro Atmega32u4 5v/16mhz Module With The Bootloader For Arduino Mini Usb/micro Usb With 2 Row Pin Header For Arduino - Integrated Circuits - AliExpress
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ATmega32U4 Mega32U4 5V 16MHz Module Pro Micro USB Controller Board for Arduino Nano Mini Leonardo ATMEGA32U4-AU with Bootloader: Amazon.com: Industrial & Scientific
Tom's computer pages
Review: SparkFun Pro Micro RP2040 - Make: DIY Projects and Ideas for Makers
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