The thought occurred to me late last night that I could replace the resistors that governed the rate of charge for the capacitors with transistors so that I could vary the rate.
Turns out I was right!
One question remains is how to vary the rate over a wider range and use a potentiometer instead? The LDR goes from about 30k all the way up to 1M, which is a pretty wide swing, and isn’t giving me all that much range in rate. You can of course get 1M pots, but they’re not as common, while I’ve got drawers full of 5k – 100k pots. If I can figure that out, maybe I’ll actually build this up proper as a Eurorack module. I’m probably going to have to use math, but not on a Friday night…