Adafruit ItsyBitsy

Another AtMega32U4 breakout board

Adafruit recently released the ItsyBitsy. It comes in two versions 5V 16MHz and 3V 8MHz.

It looks similar to the Pro Micro but has more data pins, 23 total usable (instead of 18). Some are along the bottom edge. ItsyBitsy is longer with 14 pins on each side instead of 12. It sort of looks like a Teensy LC. It even has a reset button.

It has the same Caterina type bootloader, so flashing it is the same as a Pro Micro with Avrdude.

The price is not bad at under $10 each. The build quality is much better. Gold ENIG finish. The micro USB connector's feet go into the PCB, should be harder to break off.

It comes with some header pins.  The reset button is at the bottom.

The bottom is completely flat.

The pinout with the AtMega32U4 pin names. An explanation of the other pins can be found here.

According to the schematic of the 5V version, it should also work with the VBUS power detection that the Let's Split firmware uses to determine which half is plugged into the USB port.