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Gadget Freak Case #217: Finding the Sun With a Microcontroller
6/22/2012

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This multiplexing project can be modified by adding output routines to the program to drive motors or other devices.
This multiplexing project can be modified by adding output routines
to the program to drive motors or other devices.

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Beth Stackpole
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Blogger
Placement is everything
Beth Stackpole   6/22/2012 7:14:52 AM
I could have used Jerald's gadget a couple of weeks back when we were experimenting with solar lighting in a couple of gardens in the back yard. Took a few days (perhaps more since we did it in a good stretch of rain) before we got the small main panel situated properly. Jerald's invention could have saved us some serious time!

naperlou
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Re: Placement is everything
naperlou   6/22/2012 8:05:20 AM
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This could also be used for tanning.  Either instructions could be given to the user, or a movable platform could be moved automatically.  The microcontroller could allow one to add an audible roll over tone. 

All kidding aside, it is interesting that Jerald found he had to use so many photo transistors, and that he had experimented to find the result.  Good work.

78RPM
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Gold
Re: Placement is everything
78RPM   6/22/2012 1:59:30 PM
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Yes, Naperlou, I tried using two photocells to find the brighter direction right/left. The trouble was that after the motor and photocells turned, they now found another decision -- go right or left.  The motor turned erratically.  I looked at charts of the sun's path and found that 110 degrees of east/west scan would be a useful range of solar energy for any latitude up to 49 degrees.  30 samples gives us 3.67 degrees of precision, so the the microcontroller could go to sleep for 3 minutes between scans. -- Jerald C

78RPM
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Re: Placement is everything
78RPM   6/22/2012 2:03:41 PM
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Thanks, Beth, I'm working on documenting my work with directing a motor to do the output portion of this project.  For now, I hope others see its usefulness as an input device to multiplex many inputs to a single pin. -- Jerald C

Charles Murray
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Today's method?
Charles Murray   6/22/2012 5:12:11 PM
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Jerald: What method (prior to yours) have solar panels used to find the sun?

Nancy Golden
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Platinum
Great Project
Nancy Golden   6/22/2012 5:19:32 PM
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I think this is a great project - very useful for efficient collection of solar energy! I particularly like PICs for these types of projects - they are so versatile and just plain fun. The inexpensive programmers that Microchip sells don't break the bank either and their MPLAB IDE is free and very user friendly. Great job!

78RPM
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Re: Today's method?
78RPM   6/22/2012 5:41:29 PM
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Charles,

Your question is exactly the one I asked when I started the project.

Their methods are probably proprietary but I believe most of them would use the brute force method of calculating the sun's position. If one searches for solar position calculations, one finds that the calculation is far from simple.  While C code is available free online, it would take a microcontroller that supports a multiple precision instruction set, an input of latitude/longitude, current time, real time clock, look-up trig tables, etc.  While my approach is not purely minimalist, I wanted my device to just look up and say, "Where's the sun?"

Jerald C

mrdon
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Re: Great Project
mrdon   6/23/2012 3:28:07 PM
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Nancy, Microchip provides a variety of cool PIC micrcontrollers and tons of great app notes and source code examples. I've used them in several projects and the ease in which to get them running is truly amazing. This project is just one of several examples of how microcontroller technology can easily be implemented. Great project idea!

notarboca
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Source Code
notarboca   6/24/2012 10:33:54 PM
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Jerald, your project is wonderful and stimulating on a number of levels.  It is simple and elegant, from the design, to the selection of microcontroller for your purpose, to your use of multiplexing.  Perhaps I have missed something, but is source code available for this project?

Thank you so much for sharing this excellent design.

j-allen
User Rank
Gold
Solar tracker
j-allen   6/25/2012 9:25:31 AM
This is indeed a clever solution to a non-problem.   We would really need it if  the sun behaved like an aerobatic airplane.  In actuality it "moves across the sky" at a reliable 15 deg/hour, so a simple clockwork or synchronous-motor heliostat is perfectly adequate.  Even if there were a small aiming error, the derivative of the cosine is very weak in the vicinity of 0 deg, so your solar panels would still produce full output. 

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