Yamaha DTXpress/DTXplorer/DTXtreme

One other point which you will find out when researching DIY edrums -
people making their own cymbals (or snares/toms) find it tricky to
duplicate the rim switch so often use two piezos to get dual zone
cymbals.  With many modules this causes a problem because you need to
use two inputs to use two piezo signals.  The DTXpander circuit in the
files section here turns two piezo signals into a single piezo signal
plus rim switch so you only need one input.

Keith.