solar tracking system

Discussion in 'The Projects Forum' started by george62, Dec 7, 2011.

  1. george62

    Thread Starter New Member

    Oct 22, 2011
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  2. george62

    Thread Starter New Member

    Oct 22, 2011
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    i am trying now for days to understand how this values of resistances came out and i cannot find it please someone if can help it will be really appreciated
     
  3. wayneh

    Expert

    Sep 9, 2010
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    Here's your circuit. (Right?)
    The resistor dividers define the voltages at which the op-amps switch from one polarity to the other as the light falling on the two LDRs changes. The value you need depends on the specific LDR and a complicated set of factors, that's why the variable resistors are there, to allow adjustment for the specific components.
    [​IMG]
     
  4. george62

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    Oct 22, 2011
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    yeah but lets say i want to use 24k ldr then the values of the resistors are ok or they need to be change ?
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Depends on what was used in the original design versus what you plan to use.

    Do you have data on your LDR showing resistance versus illumination? With that you can estimate what resistors you need.

    Me? I'd experiment. But I have a resistor assortment from which I can assemble almost any divider arrangement. It's harder if you're trying to guess what to buy, hoping it will work when it arrives.
     
  6. george62

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    Oct 22, 2011
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    yeah but i want to make this for my class presentation and i have to calculate from where to get those resistor values do you have any suggestions ?
     
  7. george62

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    Oct 22, 2011
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  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    You need to calculate when the LDR voltage divider will turn on one comparator and turn the other comparator off, and vice-versa.

    This is done by calculating the voltages produced by the two voltage dividers, each consisting of a fixed resistor and a variable resistor, and by comparing the resistance of the LDR in full sunlight to the resistance of the LDR in partial sunlight. Response shouldn't be so fast that a passing cloud will cause it to aim erratically.
     
  9. george62

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    Oct 22, 2011
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    yeah i dont know how to calculate them can you help me a bit more pls ?
     
  10. thatoneguy

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    Feb 19, 2009
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    You'll need a DMM, the two LDRs you plan to use, and one sun.

    When all three are together, measure the resistance of both LDRs separately when they are fully lit by the sun.

    Then tilt one about 45 degrees or so away from the sun and see what the resistance reads, do the same for your other LDR.

    These are the two resitances you'll need to make in the voltage dividers. I'd suggest 10 turn precision pots for both, maybe 50k or 100k depending one what you got for measurements above. You'll want to make them almost, but not quite, equal, with some hysteresis (that means once it moves, the other side needs to go darker than 'normal' to move back), that will prevent it dancing around cloud shadows.

    In the example above, you'll see they used two widely different values for the voltage divider. This is so it only takes a little difference to track to the west, but a big difference (such as sunrise) to track east.

    The comparators output goes in the direction of whichever input is greater, so you NEVER want them to give the same output (both + or both -) plan for that.

    Google "Voltage divider calculator" for an online resistor voltage divider that is quicker than a formula.
     
  11. george62

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    Oct 22, 2011
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    thanks for the information but i want regarding this kit to design a similar one and i want to make the calculations for the components to be used is there any suggestion for this ?
     
  12. wayneh

    Expert

    Sep 9, 2010
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    This will give you very nice adjustment MUCH easier than less-than-single-turn typical trimpot, for instance.

    For explaining this in class, consider some BS based on the specs of the LDR. It's OK to be mistaken as long as you have a logical process, one that can be adjusted as real data comes in.
     
  13. george62

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    Oct 22, 2011
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    yeah but guys i still dont understand the values used for the resistances and i need to proove that those values are correct any idea of doing this ?
     
  14. thatoneguy

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    Feb 19, 2009
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    I thought I just explained how they were calculated, in pretty good detail.

    You need to know the resistance of your LDRs both in direct sunlight and at angle away from the sun to really calculate the actual numbers, which will probably not be the actual numbers when you end up building it due to tolerances, not having the same intensity of light, etc. I explained how it works, what is required for it to work, etc.

    Which part didn't you understand? I can try explaining it further.
     
  15. george62

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    Oct 22, 2011
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    because this project i am going to design my tutor wants me to give him a presentation of firstly how it operates and how it works and also he wants me to prove that the values used are the correct ones
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If you do not have the LDRs resistance measured that you are going to use, or a sun handy, you won't be able to get the exact value tonight. Tomorrow morning, again at noon, again after school, and one more just before sunset should give you a good idea of the range of both LDRs.


    If you needed this in such a hurry, why did you ask here the night before it was due?
     
  17. george62

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    Oct 22, 2011
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    this is the night before the presentation of it and i don't know what to do know ;/ because i took the schematic from this site and it doesnt explain anything
     
  18. thatoneguy

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    Feb 19, 2009
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    So "The night before the presentation" is the normal guideline you use to start projects?

    I'm gonna probably sound like your father, but you won't get very far in life with that outlook on work ethics.

    --ETA: That schematic isn't from this site.
     
  19. george62

    Thread Starter New Member

    Oct 22, 2011
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    its an idea i found to use since i want to construct a dual axis solar tracking system and i found this solution a good one is there any other simple one to use on my project ? thanks very much :)
     
  20. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Search this site for "Solar tracking" and you'll find lots of projects, though over half of them are uC (micrcontroller) controlled to account for clouds and rain (which gives both sensors the same input), so it waits.
     
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