Hi Oddio,
Just a guess here but i think you would
like to stop pointing the torch at it
when you're happy with the volume level?
I dont suppose you want to have the
brightness of the torch determine the volume?
I would suggest that your volume could go up
in little steps, and that you could point
your torch at the photo-cell, and then wiggle
the light across the cell so as to step it
up a bit at a time.
Another cell nearby could do the same
stepping down.
Such a unit could fairly easily be made using
chips.
You can get little laser toys with red rays
that would do this better than a torch,
they're only small, ive seen them on key rings.
Regards, John