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How to Wire an LED

Discussion in 'Electronics Videos' started by unix60959, Jan 23, 2012.

  1. unix60959

    unix60959 New Member

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    In this video I show you how to calculate the R value needed for your LED circuit as well as basic LED circuit setup.

    [video=youtube_share;RMaaTGcWB-U]http://youtu.be/RMaaTGcWB-U[/video]
     
    Last edited: Jan 23, 2012
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  2. edman222

    edman222 Member

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    you forgot... (9V - (0.7V drop))/680 ohms = Current .... is what the current would be.
    That is important for LED's that have a high Vdrop such as supper brights (which can be as high as 3.7V) Thus for a supper bright it would be (9V-3.6V)/x ohm's.. If you just use the 9V/680, your LED would be ON but dim and you wouldn't realize the full brightness.
     
    Last edited: Jan 23, 2012
  3. JimB

    JimB Super Moderator Most Helpful Member

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    No you did not show how to calculate the resistor value, you showed how to calculate the current when the resistor value is known.
    Not the same thing at all.

    While doing the calculation you forgot to take into account the forward volt drop of the LED.

    The forward voltage drop (Vf) of a basic red LED is not 0.7 volts, it is nearer to 2 volts.
    I just did a quick test using some LEDs I have to hand and they showed a Vf of 1.9 to 1.95 volts.

    As edman pointed out, not all LEDs are the same, the Vf varies with the colour of the LED, some can be as 3 or more volts which makes big difference to the required resistor value.

    I realise that this video clip was made for beginners, but your description of the purpose of the resistor was poor, almost to the point of being wrong.

    Sorry, but your video just does not come up to scratch.

    JimB
     
  4. dave

    Dave New Member

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  5. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    Sorry Jim but I disagree..... At least he has tried... Its quite clear in the video that it's a bog standard LED... People have to start somewhere..

    unix60959... Don't worry about the negative comments.. The video is a good start... You can always edit it to take these comments onboard.

    No disrespect intended to both of you.. You are both highly qualified, but constructive comments go a lot further.
     
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  6. unix60959

    unix60959 New Member

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    I actually made this video a long time ago and at the time had no formal education in electronics. I know now that in order to solve for R you have to subract the the voltage drop of the LED from the Vs. but since most LED's are .7V forward bias I felt that it was negligable... and not worth making another video. When ever people commented on my video about using 3.2V LEDs or adding multiple LED's I told them the new formula. I will make a new video in the future to clear these things up.
     
  7. JimB

    JimB Super Moderator Most Helpful Member

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    Incorrect.

    A silicon diode has a Vf of about 0.7v, but Vf of an LED is significantly higher, depending on the colour and the doping used in the semiconductor used to give that colour.

    JimB
     
  8. Reloadron

    Reloadron Well-Known Member Most Helpful Member

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    Unix,

    Hang out a little, snatch some new material and remove and replace Video 1 with Video 2. While Video 1 does have inaccuracies the new and improved (I love that term) Video 2 will be accurate and on target. Live and learn as the saying goes.

    Ron
     
  9. JimB

    JimB Super Moderator Most Helpful Member

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    As the main critic of the video, I am in complete agreement with Ron:

    JimB
     
  10. Stratus

    Stratus New Member

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    If I may add my two cents worth unix60959 I think a writing a script for the next video (which by the way I'am looking forward to seeing as this is a good start!!) would be a good idea, that way you have less things to be thinking about.
    I especially liked the drawn diagram and laying the actual parts next to there symbols VERY good idea. Is there away I could get notice of take 2??
     
  11. Sceadwian

    Sceadwian Banned

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    http://www.oksolar.com/led/led_color_chart.htm

    Might help new users approximate the VF of the diode, keep in mind all the listed voltages are at 20ma current, which is nominal for typical LED's, higher power LED's can handle more current but generally need to be heatsinked to maintain the same voltage drop, heating (including ambient temperatures higher than the data sheet) can drastically increase the diode's voltage drop often catastrophically, if not with a significantly shorter life.

    Your specific tutorial approximated pretty good for a low power RED diode, but if you made the same assumptions on something like a bright white LED, you'd lose 50% or so of hte brightness because it wasn't being fed the appropriate current. The devil is in the details.

    I'm definitly with Stratus, the production was decent, but you really have to work out a script, the number of throat clearings and umms makes for BAD video. If you want good quality tutorials you either have to offload the video/audio production on to someone else or learn it yourself.

    If being a teacher were simple the whole world would be smart because the most intelligent could instruct those with public speaking abilities as to how to inform the masses. Such is not the case.
     
    Last edited: Feb 10, 2012
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I have never seen a tutorial with so many things wrong in it.
     
  13. harold777

    harold777 New Member

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    unix60959 I think if you are posting vids they should be visually clear, that means no wobbles as the camera moves and then the vid should stand Technically, the notion that most LEDs are 0.7v is wrong.

    You could add a "confirmation" (of the LED current), by measuring the voltage across the Resistor. I think that would satisfy the several issues pointed out by other posters. A DVM might not show on the screen, but a cheapie m/c multimeter has minimal burden for this measurement.

    Keep on trucking.
     
  14. KJ6EAD

    KJ6EAD Member

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    Last edited: May 26, 2012
  15. flinty

    flinty New Member

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    well guys after those negative comments how we can calculate the resisor for the LED??in that case
     
  16. KJ6EAD

    KJ6EAD Member

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    R = (Vs - Vf) / Iled where Vs is the voltage of a well-regulated supply, Vf is the nominal forward voltage of the LED at the design current and Iled is the design current.
     
  17. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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  18. flinty

    flinty New Member

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  19. flinty

    flinty New Member

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    i think that Maximum Permissable LED current Limit milli-amps is that maximum value of current that LED can work on it after it the LED is break down or operate at reverse mode??

    if i9 wrong you tell me,vuz iam beginner:)

    thx dude.
     
  20. Sceadwian

    Sceadwian Banned

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    This is the current limit for the LED.. Pretty basic. The vast majority of common LEDs have current limiteds of 20ma, with some bright LEDs handling 30ma without much trouble, beyond that it's up to the datasheet for your specific LED.

    It has nothing to do with reverse conduction of a diode this is not taken into consideration in a resistor calculator typically.

    If you want to be safe, assume this current is 10ma and run your calculations from there, your LED's will last many times longer than one run at it's fully rated current and will consume less power but still provide an appreciable amount of light. Considering the main goal of many LED setups is to simply be able to be seen (often in the dark) not necessarily as primary illumination extracting every lumen of brightness out of the diode isn't as high a goal as you might think. Given running a diode at 10ma vs 20 consumes half the current, it generates 1/4 the heat and more than doubles the LED life yet will produce more than 50% of it's rated light output at full current, so it's always more efficient to under current an LED from it's maximum specs.
     
    Last edited: Jun 8, 2012
  21. flinty

    flinty New Member

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    that was pretty but if the current value exceed Maximum Permissable LED current Limit milli-amps??
    what is gonna happen ??
     

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