Send this PWM signal to a MOSFET or something ... Instead, he built his own with an ATTiny and an H-bridge motor driver. No surprise, it works, but what’s interesting is what effect the code ...

This particular setup is a half H-bridge. It allows you to drive the motor in one direction only. The MOSFET used on the ground-side of the motor doesn’t actually need to be there. This is the b ...