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Problem with wiring project

Discussion in 'General Electronics Discussion' started by Phil Brown, Mar 4, 2015.

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  1. Phil Brown

    Phil Brown

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    Mar 4, 2015
    I have a project I found on Instructables:
    http://www.instructables.com/id/Magnetic-table-lamp/

    I'm trying to duplicate this on the breadboard. I wired the circuit board up the way you see in step 5.
    After that things get very sad.

    I know that on the Bridge I connect the Positive to the ~ and the negative to the other ~. I believe how the bridge is designed is that it doesn't matter which ~ I connect to. But the LED's I'm having a tough time finding where I connect those. One end to 1 of the resistors I get, but the other end doesn't connect to the other resistor does it?



    Thanks for the help/
     
  2. KTW

    KTW

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    Feb 22, 2015
    Did you see the schematic?

    [​IMG]
     
  3. Phil Brown

    Phil Brown

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    Mar 4, 2015
    I did and I just am too much of a novice. Although I think what I should do now is connected 2 LEDs to a resistor and then the other end to the capacitor. And then the other 2 LEDs to the last resistor and then to the same resistor.

    Close?
     
  4. KTW

    KTW

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    Feb 22, 2015
    I'm just as much a novice Phil but what I see are two sets of LEDs, each pair connected to a resistor and then the ends of both those resistors are connected to the negative side of the capacitor.
     
  5. Phil Brown

    Phil Brown

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    Mar 4, 2015
    You are correct! I think I have a component sized incorrectly, the LEDs are on but then in 20 minutes burn out.

    But hey that's a start.
     
  6. KTW

    KTW

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    Feb 22, 2015
    It calls for 1 Watt resistors and you are only using 1/4 Watt.

    6.8 uF capacitor.
     
    Last edited: Mar 5, 2015
  7. davenn

    davenn Moderator

    13,877
    1,964
    Sep 5, 2009
    Hi Phil

    Instructables are notorious for poor circuits etc on their site

    OK if your LEDs are burning out, up the resistor values somewhat, 39 Ohms seems way too low.
    With 12V, I would be using something around 1000 Ohms (1k)

    you mite want to have a look here .....
    https://www.electronicspoint.com/resources/got-a-question-about-driving-leds.5/
    its a resource section on this forum site all about driving LEDs, you may find it very helpful :)

    cheers
    Dave
     
  8. Phil Brown

    Phil Brown

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    Mar 4, 2015
    Hey thanks everyone.

    I am measuring 13.9V across the circuit.

    Dumb question, why is it negative on my multimeter?

    Sorry for all the dumb questions, I will try upping my resistors!
     
  9. davenn

    davenn Moderator

    13,877
    1,964
    Sep 5, 2009
    1) do you have the red and black probes on the correct places ? red = positive, black = negative
    2) do you have the red and black probes in the correct sockets on the multimeter ?


    show us a photo of your construction you may have a wiring error if you have the above 2 points correct

    Dave
     
  10. KTW

    KTW

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    Feb 22, 2015
    The DC supply may be reversed.
    I just bought two from Amazon and the negative is on the center of the plug.

    I just noticed the LED's you are using don't match either.
     
    Last edited: Mar 5, 2015
  11. BobK

    BobK

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    1,688
    Jan 5, 2010
    The circuit is designed for 150mA LEDs. You are using what are probably 20mA LEDs. No wonder they are burning out. And if you change the resistors to make them run at 20mA they will not put out much light. And they are narrow as opposed to wide angle. Really not suitable for this project.

    Bob
     
  12. Phil Brown

    Phil Brown

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    Mar 4, 2015
    Thanks Bob.

    I can't see on the Amazon page where it says how many mA it needs, is this something that is just knowledge you have?

    Would this have been a better LED?
    http://lighthouseleds.com/10mm-5w-4-chip-led-white-ultra-bright-180-000-mcd.html
     
  13. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    You can make them work... if, you use more LEDs to compensate.
    Additionally the narrow angle can be compensated for by aiming them differently, or even taking some sand-paper and scuffing up the plastic lens to give it a 'diffused' or 'frosted' finish. Of course the sandpaper trick will give you a more uniform light, but because of this it will not project quite as well.
     
  14. KTW

    KTW

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    Feb 22, 2015
    When making a duplicate circuit you should stick with the items listed or you'll run into problems.
    LED's can be searched to find their properties.
    If you're baking the same cake just follow the same recipe.
    .5 watt led.JPG
     
  15. BobK

    BobK

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    1,688
    Jan 5, 2010
    Yep, that looks like the right one.

    Bob
     
  16. Phil Brown

    Phil Brown

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    Mar 4, 2015
    Yeah I looked at the recipe and said, "OK lets see what I can get on Amazon with free shipping." I can see where that's a dumb idea and can bite me in the ass.

    KTW, mind if I ask what website the picture you attached is from?
     
  17. KTW

    KTW

    273
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    Feb 22, 2015
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