A variable voltage switching regulator with caps and a potentiometer, handling at least 3amps. I built a vv mod using a Texas Instruments PTR08100W and it's working great, also does not get hot. Trouble is, one person buying these individually, the module is about $20, so a bulk buy from madvapes might get a price break they could pass on to us.
Would also like a smaller voltage display. But I haven't found one searching around to recommend. The RC helicopter one they sell is awesome, just a bit big.
Thank you.