Raspberry Pi Pico to Arduino Uno adapter relies on FlexyPins for castellated holes - CNX Software

Solder Party's "Raspberry Pi Pico to Uno FlexyPin Adapter" uses FlexyPins to secure the Pico board to the adapter using its castellated holes.

Solder Party's FlexyPin Adapter offers a swift way to bring the Uno form-factor to the Raspberry Pi Pico

These boards allow you to use various modules with a breadboard (and more) without having to solder the module in place. Just add FlexyPins!

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Raspberry Pi Pico to Arduino Uno adapter relies on FlexyPins for castellated holes - CNX Software

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Surface-mount connectors hold castellated modules