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Hours of sunlight in my yard? Answered

I want to find out how many hours of sunlight various parts of my yard get. I'm envisioning a solar powered clock/timer that runs only when the sun shines on it. Then at the end of the day I can see the hours of sunshine, record the number and reset the timer for a different place in my yard.


"A question, when asked precisely, answers itself" as my old dad used to say.

Just replace the battery in a cheap clock with a small solar cell. Then set the clock to 12:00 and place the pair of them in the place you want to test. The clock will run when the sunlight shines on the solar cell and stop when it doesn't. At the end of the day read what the clock says = the number of hours and minutes the cell saw sun.

Thanks for your reply, though I see two problems with your solution. First, it is difficult to find any analog clock now. And of course a digital one will go blank when the sun stops shining. Second, I don't know where to find the small solar cell you mention.

You can pick up analog clocks for $2-$3 at many thrift stores.

You can pick up a small solar panel for ~$10 at Radio Shack or many online retailers.

Do you mean sunlight or light? If you mean the hours of the day that it is light you could look it up online easily. If you want to measure the hours it's in direct sunlight see below :)

You could use a light detecting diode with a comparator circuit called a schmitt trigger. You would need to work out the resistance of the diode in the shade and in the sun and use this to trigger the comparator circtuit. When the circuit goes high because it's in the sun, it starts a timer (a hacked digital clock for instance, a lot of them ahve timers and you could replace the stop/start button with your circuit). The comparator would stop the timer when it goes low when the sun goes behind the trees/your house.

The schmitt trigger is advised as it give a buffer between on and off. If you were to do it without one you'd have a period of quick on and offs as it went over the threshold of light enough to be on.

See here for a good description of how to make a schmitt trigger circuit. http://en.wikipedia.org/wiki/Schmitt_trigger

If any of that was unclear, PM me and I'll see if I can help more :) It sounds like a fun project.

Thanks for your reply. I have looked up the hours of daylight for my location, but I do want to know the hours of direct sunlight. Your suggestion about the Schmitt trigger involves more complexity than I want to get into.