light tracking device

Discussion in 'The Projects Forum' started by panofish, Dec 20, 2007.

  1. panofish

    Thread Starter New Member

    Dec 20, 2007
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    I built this tracking device in college ... I dug it out of the basement and added information about it onto my projects blog. You may find my blog interesting. Feel free to browse all the projects on my blog and provide feedback and questions.

    http://home.comcast.net/~panofish/WEBLOG/2...vice/index.html

    [​IMG]
     
  2. bundick

    Active Member

    Dec 19, 2007
    97
    1
    Boy that looks complex. Something a College kid would do.
    I went to a lab where they test Solar panels.
    Those guys programmed an old TRS 80 to know where to point the Solar panels every morning and what the arc of the sunlite would be during the day of each day of the year.
    I'm not that talented, but that's what I'd do if I could.

    I had one in mind that had four Cad Cells. Top, bottom, n' sides.
    An RC timer that looked at the voltage levels from the Cad Cells.
    It turned on a relay to make a motor turn the dish until the two voltages were the same and that dropped out the Relay. In a few minutes the Timers would have the Voltages checked again. All day long. You get a lot of sunlight even on a cloudy or snowy day.

    The two motors turned the dish toward the brighter Cad Cell keeping the Dish facing the sun as best it could all day long.
    After dark the Motors would turn the Dish back to the Home position, looking for the sun again.

    I think a guy could make a Solar battery charger and that thing would run forever.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Nice job :)

    Take a look at microstepping that motor; it'll reduce the "jitter" you're getting when it's locked on to a stationary flame.

    You might want to put a bit of aluminum foil over the window on your EEprom so you don't lose it's contents.
     
  4. panofish

    Thread Starter New Member

    Dec 20, 2007
    5
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    microstep? How do I do that?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    You're using a unipolar (6-wire) stepper motor, right?

    You know about normal stepping already.
    1000
    0100
    0010
    0001
    1000
    ... etc
    And half-stepping goes like this:
    1000
    1100
    0100
    0110
    0010
    0011
    0001
    1001
    1000
    ... etc.

    Now imagine that instead of just jumping into each half-step, we used PWM to gradually ease into it by starting at a low pulsewidth, then increasing the pulsewidth while decreasing the pulsewidth to the pole that the armature is moving away from.

    You'd want to use a PWM frequency that's above the range of hearing; say 25KHz to 30KHz - yet not so fast that your PWM driver spends too much time in transition, or you'll wind up with a room heater. ;)

    It also appears that your tracker logic does not make use of ballistics; when the sensors report that the difference is large, your motor should step quickly; as the sensors approach equal output, the steps should be smaller and therefore slower rotation. The result would be that you would seldom wind up in an overshoot condition with 'jitter' as you are now.

    You might be able to accomplish the majority of it (reduction/elimination of jitter) by switching between full- and half-stepping, and varying the rate of acceleration porportional to the difference in the sensor readings. If your stepper is 1.8 degrees/step, you'll get 0.9 degrees per half-step. That would likely be sufficient resolution for the close ranges you're dealing with.
     
  6. panofish

    Thread Starter New Member

    Dec 20, 2007
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    Wow... You explanation is awesome and clearly shows your experience/knowledge in this area. Realistically, I may not revisit this old project, but this info may prove useful on the next one. THANKS!
     
  7. Reshma

    Active Member

    Mar 11, 2007
    54
    0
    Hey that's really cool! I am doing the same project but I am using a PIC micro controller. So I don't need an ADC chip since the PIC has a built-in ADC port. However, I am still wondering on how to mount the sensors on the Stepper motor. Can anyone give some good suggestions?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Did you look at the photos and the video on Panofishes' website?

    Admittedly, he got lucky and found something nearly perfect for what he was doing; a parabolic reflector with a holder at the focal point. You're going to have to work a bit harder, since Radio Shack discontinued that item a long time ago.

    You could make a reflector from a piece of aluminum foil wrapped over a spherical shape, and experiment with a directional beam (laser pointer, perhaps) until you located the focal point; then mount your sensor(s) at that point.

    Looks like your benefactor just used a couple of machine screws with nuts to hold his reflector to the motor shaft - might've used heat shrink tubing to extend the shaft.

    It's your project - get creative ;)
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Reshma, I stumbled across this page:
    http://store.sundancesolar.com/sospliposiso.html

    Very similar to the solar-powered cigarette lighter that Panofish used. However, it's $12.95 + shipping; pretty expensive for what it is.

    I've found small round stainless steel mixing bowls for sale at my local grocery stores; they're under $5 each. You could get something like that, and very carefully cut or grind a round or oval reflector from it. The metal is very thin, so you'd need to use something like a Dremel tool in order to avoid distorting your homemade reflector. Still, it would be far sturdier than simply using aluminum foil.
     
  10. panofish

    Thread Starter New Member

    Dec 20, 2007
    5
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    That would work, just make sure your your not going to track the sun. Otherwise you'll melt your sensors... :)
     
  11. Reshma

    Active Member

    Mar 11, 2007
    54
    0
    Yes, I went through Panofish's videos and images. I must admit that they were really good and gave me a good insight on my own project. I was struggling to find a way to mount the sensors....my teacher was giving some outrageous suggestions but the method which Panofish has adopted is good. I don't wish to track the sun...and my budget isn't that impressive either..LOL. I will post my developments once I get started. Thanks for your help!
     
  12. panofish

    Thread Starter New Member

    Dec 20, 2007
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  13. SgtWookie

    Expert

    Jul 17, 2007
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    Interesting. :)

    However, rather than using discrete transistors for drivers, you could use ULN2003 or ULN2803 IC's; they are (respectively) 7 or 8 Darlington pair transistors in a single IC, configured as open-collector outputs. They're made specifically for driving inductive loads such as motors and relays; they have built-in diodes to take care of the reverse EMF when the current flow is interrupted. The ULN2003s are more for driving things like 7-segment displays, but can also be used for motor/relay control. One ULN280x is sufficient to drive two unipolar (6- or 8-lead) stepper motors. This will reduce your parts count significantly.

    The ULN2x03's are for TTL level signals; if you're using CMOS, use ULN2x04's. Each Darlington pair will sink up to 500mA, at up to 50V.

    Instead of connecting the stepper's common to ground, connect it to your stepper's supply.
     
  14. Reshma

    Active Member

    Mar 11, 2007
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