Peter Todd wrote:
> I got everything right, something more like 220ohms would still give
> me sensitivity at both ends,

Just keep in mind that this will draw up to 23mA in very bright light.

> 1k ends up at a zero slope long
> before the CdS saturates.

Your circuit will be most sensitive to variations in the cell resistance at
mid range.  In other words, when the cell resistance equals the pullup
resistance.  The important question is what range of light you care about.
Measure the cell resistance at the two extremes, then design your circuit to
resolve that range at the required accuracy.


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