> It looks nice, but what I don=B4t know, and I cannot figure it out from
> the datasheet either, how much light does it need to work, what is the
> minimum light level, there may be the problem, because night sky may
> give some lx when the moon is up and big and sky is clear, but if not
> you may have 0.0.... lx or less. So it depends on what is needed. The
> spectral response curve also isn=B4t really what you would want for the
> task. Anyway, seems a nice part, I have done se same, just lot bigger
> using standard parts.

The sensitivity to light and spectral curve are functions of it being a
silicon sensor. Unless you add filters (which will reduce the overall
sensitivity anyway) the spectral response will be the same for any
silicon sensor. The limiting factors are the sensitive area and
temperature. PIN diodes come in a variety of (large) die sizes to
give you more collection area. The problem is that they are just as
sensitive to heat and you have more heat collecting area as well.
You can see from the datasheeet for the device that heat is the
limiting factor as the light levels get low.
The sensitivity is given in the datasheet as uW/cm^2. One lux is
about 5uW/cm^2 (they aren't directly related but that is a guide). A
moonlit night is around 0.2 lx and a starlit scene about 0.01 lx.

You may want to experiment with LDR's. I was using one in a
project and noticed that it was really sensitive to changes at low
light levels. ie. There was a difference between being in a closed
drawer inside one piece of black heatshrink and having two layers
of heatshrink. I didn't investigate any further than that though.

Steve.

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Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: steveb@tla.co.nz      fax +64 9 820-1929
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