On Sep 11, 2:48*am, "Dave Plowman (News)"
wrote:
[my device] fades up to max when a simple DC switch is made, then
fades out when it is broken. I can get it to do this using a simple RC
circuit - but the 'law' of the fades isn't as linear as I'd like. Any
clever way of doing it?

Use an RC circuit, but clamp the range to a fraction of the full sweep
with diodes. R goes to [0 , +5] volts at your switch, but
the capacitor only goes to [+2, +3] volt range, which is much
more linear... or [+2.3, +2.7] volts, if you prefer.

It'll take two op amps for the clamps, and one or two to amplify up
the small range to the full voltage swing and polarity you want.
LM324 and a couple of diodes, one capacitor, and resistors.