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LED Flash light ..Pulsed LED, underdamped oscillations

Discussion in 'General Electronics Chat' started by williB, May 24, 2005.

  1. eblc1388

    eblc1388 Active Member

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    Try using beepers instead. With a bit of careful design, you can make them sound like crickets. Put nature right into your living room. :lol:
     
  2. Someone Electro

    Someone Electro New Member

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    then lets continue the discuion on Shaker generators,LEDs,caps,PWM,constant curent surces...
     
  3. williB

    williB New Member

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  4. dave

    Dave New Member

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  5. williB

    williB New Member

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    8) I dont know how big those two files are ,but if you have dialup it may take a long time..
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Hey Willie,
    The Putfiles play! I heard your shaker in the background going like crazy and saw the motors turning rather slowly. Do you have enough power to drive an LED brightly?
     
  7. williB

    williB New Member

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    i think so ..
    i found this relationship on a ultra capacitor site. maxwell i think..
    t=CV/I , a dirivation of Q=CV..
    @ I = 10 mA and 2.2 F worth super caps.. and 5.5 V
    should give 20.16 min. of light
    and 4.3 sec of charging @ 300mA..
    the white led is pretty bright at 10 mA..
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    If you use a constant current circuit (that needs extra voltage) for the LED, after 10 minutes the cap's voltage will be down to 2.75V, won't it?
    The LED might be powered for only 5 minutes.

    I think your generator's current was measured shorted, with no output voltage. I think the current will drop exponentially as the cap's voltage rises during its charging, causing the charging time to be much longer.
     
  9. williB

    williB New Member

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    You are right , my mistake , i was calculating for a full discharge of the caps, wasnt I ?
     
  10. williB

    williB New Member

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    how about if i put a rechargeable battery below the caps..

    not really , if you recall i was using a crappy ammeter , and was getting about 3V Peak with it connected directly to the diode bridge output..
     
  11. williB

    williB New Member

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    it was one volt ,a little over ..see page 2..
    so yeah, it will take longer than 4 seconds.
    my goal was 30 seconds..of shaking for 20 min. of light..
     
  12. williB

    williB New Member

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    actually let me check .. that pic on page 2 was an older one it only had ten peaks , i'm getting fourteen now , page six..
    EDIT:: ok i was right the first time it is 2.75 V Peak @ over 250mA..
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The cap will charge with average current, not peak. You will be shaking until your arm falls off! :lol: :lol:

    What's the 10mA light for, a book-light? Can you read while you are shaking the generator? :?:
     
  14. williB

    williB New Member

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    *sigh* , what are you talking about ?
    i thought we have been all through this?


    at present i am getting over 250 mA average current @ 2.75 V same as the pic on page 6 ( just smaller)
     
  15. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The max voltage for the super-caps is 5.5V but your shaker puts out 15V.
    How are you going to limit it?

    TI used to have a low drop-out current source IC but I couldn't find it. What are you going to use to regulate the LED's current as the cap's voltage falls when it is discharging?
     
  16. williB

    williB New Member

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    i'll cross that bridge when i get to it..
    probably tommorrow or the next day the super caps will arrive..
    i was thinking of a PIC driving a constant current source with PWM ..
     
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Why do Americans wait so long for delivery?
    I'm in Canada and I can order something from an American distributor like Digikey or Newarkinone tonight, and it will be delivered tomorrow morning, even after it goes through customs.

    When you overvoltage the super-caps, I wonder if they will just short, or go "POP". Did you order extras?
     
  18. williB

    williB New Member

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    No extras.. just 10 (.22F ) for a total of 2.2F at 5.5 V..
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Oh goody! All 10 super-caps won't be exactly the same, so will overvoltage sequentially, like a string of firecrackers. Please post the video. :lol: :lol:
     
  20. Someone Electro

    Someone Electro New Member

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    Meaby an 5V zener drivng and transistor circut so it will disconect the charger wen reachng 5V.
     
  21. williB

    williB New Member

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    I finally connected all ten .22F caps together , in parallel, for a total capacitance of 2.2 F.. :shock:
    G1 is two NiMH batteries at 2.26V :: NOT enough to light the led , by itself..
    R is 280 ohms
    after charging them up to 5.5 V and after turning on the switch , the initial current was 15 mA..
    After 19 min. current was 4.5 mA
    After 20 min. current was 4.2 mA.. still plenty bright..
    that is with out blinking , at all..
    it took 3min 22 sec to charge them up to 5.5 V
     

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