Peter,

On Mon, 06 Jun 2005 14:49:17 +0100, Peter Onion wrote:

> On Tue, 2005-06-07 at 00:43 +1200, Jinx wrote:
> > > I want to add a light level sensor to a clock I'm building so that at
> > > night the back light is dimmed.  ( I could use the time of day, but
> > > sunrise/sun set calculations look a bit hard for a PIC (lots of trig)).
> > 
> > Could be done with a table
> > 
> > http://www.astro.uu.nl/~strous/AA/en/antwoorden/zonpositie.html#v164
> 
> The downside to this is you need to know where you are to calculate the
> sunrise/unset times.  I don't have a method to enter those details.  In
> reality I could just put lat/long for my house into the code and that
> would be good enough (until I move !).

Another downside is that knowing sunrise/set times isn't good enough to predict the light level - the time 
when you need to switch house lights on here can vary by as much as a couple of hours on consecutive days 
depending on the cloud cover.  Much better to measure the actual light level.

Cheers,


Howard Winter
St.Albans, England


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