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Re: Bob Pease must be rolling in his grave.
8/20/2013 1:03:45 AM
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78RPM

Iagree, photoresistors response time is quite slow when reacting to sunlight. IR LEDs maybe a better choice because of their fast respones time and wavelength associated with the sun. I know Forrest Mims have done a lot of work in sun tracking using IR LEDs as well as traditional red LEDs. You should be able to find his published worked on this subject at his websites listed below.

http://www.forrestmims.org/

www.sunandsky.org

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Re: Bob Pease must be rolling in his grave.
8/7/2013 5:18:14 PM
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mrdon, I actually started my project by trying to use two pairs of photoresistors to find the sun -- one pair for vertical and a pair for horizontal.  I discovered that photoresistors are too imprecise and too non-linear.  They always ended up cockeyed.  If you wish to point a parabolic cylinder at a water pipe, your aim must be within 3 degrees of error.  I may publish a revision showing how to use Gray code converters to sense and control position.  I would probably take the easy way out on a second pass and just use an Arduino board.

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Re: Bob Pease must be rolling in his grave.
8/7/2013 5:11:20 PM
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@charly5139  Pointing a collector directly at the sun is more complicated than you assume. Your clock method would work if:

1. The earth were a cylinder.
2. Its axis of rotation is perpendicular (90°) to its orbit.
3. Its orbit is a circle.

None of these is true. Earth is approximately spherical;  It is tilted by ~23.5°;  Its orbit is elliptical.  You can find C programs online for calculating the sun position. It takes about 9 pages of C code.

If you have a parabolic channel and wish to focus the sun along a water pipe, your aim must be less than 3 degrees in error.  See http://www.analemma.com/ for a good explanation of the sun's path through the sky.

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Iron
Re: Bob Pease must be rolling in his grave.
8/27/2012 11:04:50 AM
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Yes!  I remember reading that article 30 years ago.  Would you be able to point me towards a copy of it?  Thanks.

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Re: Any Analog Solutions?
7/22/2012 9:34:50 PM
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The motors were probably driven by discrete or IC based H-Bridge circuits. These circuits are commonly used to provide directional control for motors.

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Re: Bob Pease must be rolling in his grave.
7/22/2012 9:22:00 PM
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I remembered Forrest Mims describing his solar tracking device in the defunct Science Probe Magazine. It consisted of an analog circuit driving a dc motor. The detectors for the circuit were solar cells attached to the dc motor. Based on the sun's position,  the motor will point the solar cells in the direction of the sunlight. As explained and demonstrated in this project, a small microcontroller can enhance the performance of such a basic sun tracking device. Cool project!!

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Iron
Re: Bob Pease must be rolling in his grave.
7/22/2012 5:04:59 PM
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Here in Europe, I would choose a microcontroller with a built-in RTC (real-time-clock). Knowing time and date, I can predict when the sun appears on the horizon, the elevation and when it disappears again in the evening. On cloudy, rainy days it might be useful not to switch on the servos. However, if the sun shows some erratic behavior which makes it necessary to follow it by an X/Y-tracker, your circuit might be better... (but I've never seen this on our planet).

Regards

Charly

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Re: Bob Pease must be rolling in his grave.
7/5/2012 1:06:56 PM
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@Jerald,

I have my old design for sure. All this interference and "chatter" can be eliminated by integration and delay of a signal that is usually splendidly done by installing a capacitor in the output driving circuit.

Best Regards,

Chris

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Re: Bob Pease must be rolling in his grave.
7/4/2012 6:45:39 PM
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Hi, Chris,

I mostly agree with you. In fact, I tried connecting four photocells to four opamp comparators. I ran the non-inverting of one into the inverting of the next one in a ring.  The binary search for right/left, up/down didn't work.  It kept getting distracted by clouds and rocks and shadows and the motors went wild like a hound dog on a scent.  If anyone has an efficient analog design, I'm interested.

But, again, I'm disappointed that everyone focuses on the solar application -- but then I guess I should have changed the title.  The circuit and program is really about multiplexing in general.  When I did aircraft flutter tests back in 1980 this little circuit would have been more powerful than the DEC PDP 11/70 we were using.

Jerald Cogswell

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Re: A question of efficiency
7/3/2012 12:54:34 PM
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Thanks, Mydesign. We are certainly eager to see the gadget.

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