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LED and wall adapters

Discussion in 'General Electronics Chat' started by airbrush, Jun 11, 2005.

  1. airbrush

    airbrush New Member

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    This is where i measured the voltages from...i guess i'm not sure what you mean by measuring 'across' the resistor then?? I assumed the 5.36 value here is measuring across the resistor :? ...sorry i'm a noob, can you tell :p
    [​IMG]
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It means one meter probe at each end of the resistor, so you measure the voltage actually dropped across the resistor. The same with the LED's, place one meter probe at either side of an LED to measure it's voltage drop.
     
  3. airbrush

    airbrush New Member

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    thanks for clarifying....will check again tonite
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    This circuit will work for the green LEDs but the pot will have some slack when the LEDs are off.
     

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  6. airbrush

    airbrush New Member

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    okay here are my readings

    orange pot min:
    2.77 vout
    0 at the resistor
    1.29 at the LEDs

    orange pot max:
    11.27 vout
    7.43 at the resistor
    1.9 at the LEDs


    green pot min:
    6.02 vout
    0.68 at the resistor
    2.67 at the LEDs

    green pot max:
    11.48 vout
    4.97 at the resistor
    3.18 at the LEDs

    ...i'd like to use the same circuit as before as i already have them made...just need to swap out the resistors once this is figured out
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    This circuit is for your orange LEDs.
     

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  8. airbrush

    airbrush New Member

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    okay thanks...these schematics are slightly different from the originals...an extra 0.1 capacitor in there....is this necessary??

    Will the other one work properly by just changing the resistors to the values you have in these new ones without adding the capacitor??? :?
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    All circuits in the datasheet show a capacitor on the output of the regulator to keep it from oscillating if your wiring isn't perfect. Use a ceramic disc capacitor.
     
  10. airbrush

    airbrush New Member

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    i mean as compared to the schematics on the previous page....there is another capacitor in there the other didnt have (0.1uF)...is this necessary for this to work properly...or can i just simply changed the resistors
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The capacitor is cheap, simple and is recommended. Use it on a second circuit if the 1st one without the capacitor blows-up!
     
  12. airbrush

    airbrush New Member

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    ...will do....need to do a little more shoppin for parts, hopefully i can hit the electronics place after work tomorrow before they close. Thanks again.
     
  13. airbrush

    airbrush New Member

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    well...almost

    here's a couple pics of it so far...not complete yet.

    Still have a problem with the green LEDs for some reason....they are still dimmly on....they others all work fine :?

    What do i need to check for these? circuits are made as per the recent schematic.

    [​IMG]
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I see 10 LEDs but the circuit has only 2. What did you do? Make a bunch of these circuits?

    I would take the two green LEDs with their 120 ohm current-limiting resistor, connect them to my variable voltage supply then turn down the voltage until they were off. Then I would set the circuit's minimum voltage to be a little less.

    You can reduce the value of the 620 ohm resistor like this:
     

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  15. airbrush

    airbrush New Member

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    so basically i just change this resistor until they dim off??
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Yes, change the resistor until the LEDs are dimmed enough.

    Are you connecting LEDs in parallel? You shouldn't because then they would have different brighness levels as your display shows. Also, with LEDs in parallel then they share the current and are half as bright as they should be. Do it this way:
     

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  17. airbrush

    airbrush New Member

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    yes...that is how i have them...sorry maybe i'm using the wrong phrasing when i said paralleled series....is that not what this arrangement would be called? But yes its strange that these ones behave this way...some are brighter than others...only on the green leds are doing this...the white and oranges are fine...all the same brightness. :?
     
  18. airbrush

    airbrush New Member

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    yup the 560 resistors did the trick...not sure why why the green leds have variation in brightness??...oh well...i can live with it..its only when they are very dim.

    Here's a shot of the guts, need to tidy up the wiring a bit on the inside, slap the etched glass on front and back, then she's a done deal...woohoo!!


    Thanks again for all the help...much appreciated. :D Final assembled pics to follow soon....

    [​IMG]
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Nice going, its done! :lol:
    Some of the green LEDs were made on a warm Friday afternoon and the others were made on a freezing Monday morning. They are all different, unless you purchase "batched" ones from Agilent at Digikey. :lol:
     

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  20. airbrush

    airbrush New Member

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    ...the final assembled lamp :D

    Thanks again for all the help...wouldnt have been possible without it.

    [​IMG]

    [​IMG]
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    They look really cool and probably don't even get warm. :lol:
     

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