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Gadget Freak
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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componenx
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Iron
Re: Any Analog Solutions?
componenx   7/2/2012 4:24:00 PM
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I built a a simple tracker in the mid-80's using 5 small, matched solar cells, voltage comparators and two shading strips.  I forget how the motors were driven, just that it wasn't very pretty and it used dual battery packs.  It worked really well, though.

 I've also seen a cone shaped design which had 4 parallel holes with CdS cells at the bottom and a reference cell at the tip.

78RPM
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Gold
Re: A question of efficiency
78RPM   6/29/2012 12:13:23 AM
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Dear Mydesign,

Have fun making the circuit and entering the program.  I hope the focus of the device shifts to its multiplexing purpose. Everyone is focused on the solar application, but the sensors can be anything.

The program compares TWO banks (vertical and horizontal) of 30 analog sensors EACH. It uses one-byte precision or a maximum of 256 digital values.  256 divided by 30 sensors gives approximately 1 in 8 chance of two sensors having the same value.  If you modify the PIC program to sense all 64 possible switches of the MUX into one pin of the MCU, you should consider right justifying the bits to get 10 bits of precision or 1024 values. This involves modifying the code at comments provided in the code. Contact me with any questions.

Think of other applications for MULTIPLEXING now.

The author.

kf2qd
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Platinum
Interresting solution -
kf2qd   6/27/2012 10:33:32 AM
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That freon, or maybe Propane as it has some similar properties and is somewhat cheaper, solution for moving the collector is an interresting solution. I'll have to think about that one.

Rob Spiegel
User Rank
Blogger
Re: A question of efficiency
Rob Spiegel   6/26/2012 1:50:34 PM
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Hi Mydesign. The source code has now been added to the end of the build instructions. So, click on the build instructions link and you're there.

Mydesign
User Rank
Platinum
Re: A question of efficiency
Mydesign   6/26/2012 5:21:00 AM
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1 saves
Rob, oh thatís great. I think there after we can make/test the same product in our own lab. Hope you will provide the source code without much delay.

Gregarious2
User Rank
Iron
Re: Not very simple
Gregarious2   6/25/2012 7:58:07 PM
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Aloha kaua...

Yep, the analog quad cell / baffle arrangement worked well for detection but in a purely analog system, the servo motors were always being tickled. Digital lets you add hysteresis, averaging and any other sort of condition mediation you'd like. It's also stepper friendly. It works pretty well here in Hawai'i but I did much of my tracker work in Seattle, land of grey skies. 

Everyone usually manages to settle on a solution that works for their situation ( cost, available parts, space, time,  etc..  ) It's fun to learn from the diversity.

At 40-60K$ for a home PV system, I want to see every watt I can possibly get. I wonder if the contractor panels have to be marked" this side up"?

Charles Murray
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Blogger
Re: Today's method?
Charles Murray   6/25/2012 7:36:27 PM
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Nice work, Jerald. What I find interesting about your design is that it uses a solution that a human brain would use. No human would calculate the sun's position in order to find it quickly. Asking, "where's the sun?" should work for machines, too.

gsmith120
User Rank
Platinum
Re: Great Project
gsmith120   6/25/2012 7:25:18 PM
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Nancy, I agree this is a great project.  PIC processors are used a lot of places.  I have played around with their development kits.  It's always nice to see/read about the different projects people develop. 

cvandewater
User Rank
Gold
Re: A question of efficiency
cvandewater   6/25/2012 7:08:28 PM
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@kf2qd: You probably never measured the output of a solar panel when a cloud appears. It is simply actually - the output power is linear with the amount of light.

Since it does not get pitch dark when a cloud appears, the solar panel does not stop delivering power. It may be half the amount and on very severely overcast (dreadful dark grey rainy days as there are in The Netherlands) the output may be in the order of 10%, but they still deliver power.

Since the tracker should consume a minuscule amount of power, it has a very large gear reduction since it does not move fast, so it can be powered by a small motor and even that motor needs to operation only part time, there is no reason to stop tracking when "the sun disappears" behind a cloud. The power consumed by the tracker should be in the order of 1% of the array output and it has the potential to double the daily energy output - depending on latitude and shadowing.

At the end of the day the panels are typically parked in more or less horizontal position anyway, which is safety in case a storm comes at night.

Note that the tracker will not lose the sun even when it is clouded for a long time, since the sun has a predictable path. So, as long as you do not completely reset your tracker and it has either a clock or knowledge of the previus sun position it can continue to point the panels to the correct position even when it has no good measurements for some time (or ever - it may be completely based on time and latitude to calculate the sun position).

I wonder why so many sensors were used. I know that it is in theory possible to make a tracker with a single photo sensor, but the simplest systems I have seen always use two pairs of sensors, one in X and one in Y direction to find the sun when starting from any orientation.

78RPM
User Rank
Gold
Any Analog Solutions?
78RPM   6/25/2012 6:59:30 PM
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It's me, the author again. Does anyone have a good circuit for Gadget Freak that finds the sun with analog comparators?  I tried using several op amp comparators all voting on who had the brightest signal. It didn't work very well. Show me where I went wrong. Maybe you used your method for some other purpose.

Jerald Cogswell

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