How hard is to build a processor?



6 months would be sufficient, probably shorter periods too.
the earths's axial wobble, and orbital precession, are probably going to make it impossible do it in less than a week. OTOH if you can see the stars and planets at night that would help a lot...
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In terms of the project I've got in mind, people are really over-thinking this..... I'll be very surprised if the shadow ends up distinguishing the day with better than a couple-of-days precision anyway.
That said, two days won't follow *exactly* the same path: a fall day's shadow is going to be between two spring days' shadows, and so forth.
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Arrrgh -- I misread what you were saying, so my response didn't make much sense.
But, I still don't expect a point to necessarily correspond to two date/time pairs. Time is continuous, but days aren't. There will be a gap between any two days' shadow tracks (probably smaller than the fuzziness of the shadow caused by diffraction but there all the same). Unless two tracks exactly overlay for some meaningful part of the tracks, a given track can only intersect other days' tracks at a finite number of points points.
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The solstice is not a day it is an instant, and it does not happen same the date and wall time every year.
most years have no days equidistant from the solstice.
therefore noon (or any other hour) on most days will duplicate the same elevation of the sun above the horzon.
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Sounds like a cool idea. Would need this sort of correction : http://www.swanstrom.net/sundial/gnomon.htm
which means it could take a couple of days to 'train', in order to be certain.
For the best precision, you'd probably do a simple sliding-data- match, where maybe the last 7? days of readings, are moved along to a point of least-errors. (and maybe a cloudy-day default, where it just increments the day ?
I don't see why you think you can't get 'correct day' precision out of this ?
Pushing the actual-time precision is likely to be more challenging ? -jg
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wrote:

Possibly in March or September, but absolutely not in July or December, just look at the graph.
A 7 day period would be sufficient to figure out, if it is March or September by checking the direction of the solar movement.

That is trivial. The apparent solar diameter is 30 arc minutes and since the sun moves 15 degrees each hour, it only takes 2 minutes to move its own diameter, thus the actual noon can be determined with much better precision.
In order to get the solar mean time noon, you also need to know the approximate date to apply the equation of time.
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Hi Rick,
rickman wrote:

AMD published a lot of app notes and manuals that really catered to the 2900 family of devices. In my Great Databook Purge, they are among the few items that I kept! (along with Mick 'n' Brick, of course!)

I plan on cheating: detecting the "displayed time" and using that in a feedback loop to control the pump speed. It would probably need to be a terribly overdamped control system given all the other "cruft" between the pump and the "display".

Yes, that's my approach. We don't have enough rainfall to "self wind". I suspect it would be very difficult to keep enough water in the system to span the gaps between rains! (or, if you could keep enough water, trying to keep that water "clean" of algae, etc. over that long of a time period).
We get *lots* of sun so PV seems to be an essential part of any solution.

Ah, I don't plan on displaying the time in such a "traditional" format. :> I don't want folks to recognize it as a timepiece unless they *know* how to "read" it. Instead, it will just look like a kinematic sculpture...

*will* work "on paper" before investing lots of time building something that just turns out to be a nonfunctional eyesore.
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