A teacher I know is stuck, with only npn transistors in the supply cupboard and the need to create a reversible motor drive for an Arduino project. Reversing ‘bridges’ have four switches (relay ...

This machine uses a three-phase Dahlander motor, which has three operation modes: stop, half speed, and full speed. The motor uses a special mechanical switch to select the operating mode.

Does it just stay there and do random things? Nope, of course not! [Guido] built it with a unique control box, two Arduino 2560’s and an Xbee to communicate between them.