/diy/ - Do It Yourself

I'm making a /diy/ muscle electrostimulator thing, I need to charge the capacitor to a fixed voltage selected with a potentiometer so I can set the intensity level of the discharge, the discharge can either be pulsed, with a period from 3 seconds to 0.2 seconds, provided by a 555, or be manual, triggered by a button.
The options I'm considering are LM317 or OP amp as comparator to stop charge at reference voltage set by the pot. The cap can be discharged up to 5 times a second, so enough current should flow to allow charge it between pulses, this means voltage dividers are excluded.

Any thoughts?

>TL;DR
Want to set an upper limit to the charge voltage of a capacitor while it's discharged several times a second.