I wrote, "The scheme probably needs three photocells to be sure that the one in the middle is darker than the others. Might be able to mask it with a slit and use a fine wire gnomon, in a coarse/fine servo. Could use a variable frequency motor and precision reduction, like a phonograph turntable only much slower."
We are talking about a clock, here. Build a precision clock movement run from a precision frequency, with no regard for leap seconds. Insert differential gearing between a 24 hour period of rotation and the turntable carrying the sun sensor. Use a stepper and position sensor to operate the differential to trim the turntable to the equation of time for your GPS latitude. Now we have a turntable that should follow the sun, whether you can see it or not. Insert another differential, or use other means, to center the shadow of a fine wire on a slit with a photocell behind it. This gives the difference between actual and predicted sun position. Use another photocell to see if the sun is visible. When it is, record the actual difference. Oh, and you'll need a servo to drive a mirror to correct for solar elevation, to keep a bright image on the slit. The longer the path from the gnomon to the slit, the better. Come back in a year and see what happened. Good science takes time and lots of consistent readings from the apparatus. Wish I hadn't sold my HP-113BR clocks. They had the differential gearing to set seconds and time of day. Regards, Bill Hawkins _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
