[working, based on seeing the vid]
The disc on the picture rotates.
On the disc there are lines and circles, and on the crossings you can place magnets.
When these magnets are detected by sensors they generate midi codes.
The rotation speed and the nr of lines gives the Beats Per Minute
The pot-meters are used to add variations to the midi signal
Could this be made to produce say a drum beat ?
Definitely!