Now, Model Ms have been given a reprieve from landfills or recycling centers because of the work of [wulax] of geekhack and his Model M Bluetooth controller board. [wulax] got around all these ...

The Bluetooth module wants 3.3v logic levels so that is taken into account. The image above shows a buffer chip doing the conversion, but the Fritzing schematic on the post uses a voltage divider.