Need some assistance with using a photocell to control the
brightness of an LCD backlight.

I don't know the current drawn by the backlight, only that
the datasheet says to use a 5.1-ohm resistor from 5V.  I've
determined that the proper brightness I need is 10 ohms at
night, and 5 ohms during the daytime.  The actual curve or
transition from the high to low value is not critical, but
I want to use a photocell (rather than a phototransistor,
etc) so the transition is gradual as it gets darker.

The resistance of Cadmium Sulfide photocells goes down with
increasing light, which is the correct trend.  However, the
resistances I can find are all in the K-ohm range.  So now
I need to figure out how to (simply) translate this into the
correct resistances.

I can think of many ways to do this "digitally" using PICs,
PWM, comparators or switching-transistors, etc, but can't
seem to figure out what to do for a simple linear circuit.

Any ideas?

Thanks,
-Neil.

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