# How to Wire an LED

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

1. ### unix60959New Member

Joined:
Aug 31, 2010
Messages:
21
Likes:
2
In this video I show you how to calculate the R value needed for your LED circuit as well as basic LED circuit setup.

Last edited: Jan 23, 2012
• Like x 1
2. ### edman222Member

Joined:
Jan 3, 2011
Messages:
70
Likes:
2
Location:
Everywhere
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. ### JimBSuper ModeratorMost Helpful Member

Joined:
Sep 11, 2004
Messages:
6,391
Likes:
592
Location:
ONLINE
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

Joined:
Jan 12, 1997
Messages:
-
Likes:
0

5. ### Ian RogersSuper ModeratorMost Helpful Member

Joined:
Mar 28, 2011
Messages:
9,310
Likes:
914
Location:
Rochdale UK

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.

• Like x 1
6. ### unix60959New Member

Joined:
Aug 31, 2010
Messages:
21
Likes:
2
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. ### JimBSuper ModeratorMost Helpful Member

Joined:
Sep 11, 2004
Messages:
6,391
Likes:
592
Location:
ONLINE
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

Joined:
Dec 23, 2009
Messages:
6,801
Likes:
282
Location:
Cleveland, Ohio USA
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. ### JimBSuper ModeratorMost Helpful Member

Joined:
Sep 11, 2004
Messages:
6,391
Likes:
592
Location:
ONLINE
As the main critic of the video, I am in complete agreement with Ron:

JimB

10. ### StratusNew Member

Joined:
Apr 15, 2011
Messages:
5
Likes:
0
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??

Joined:
Oct 27, 2006
Messages:
14,047
Likes:
141
Location:
Rochester, US
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. ### audioguruWell-Known MemberMost Helpful Member

Joined:
Mar 16, 2004
Messages:
32,580
Likes:
950
Location:
I have never seen a tutorial with so many things wrong in it.

13. ### harold777New Member

Joined:
May 24, 2012
Messages:
50
Likes:
1
Location:
london, england
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.

Joined:
Jul 1, 2011
Messages:
334
Likes:
21
Location:
Earth
Last edited: May 26, 2012
15. ### flintyNew Member

Joined:
May 26, 2012
Messages:
26
Likes:
0
Location:
Cairo-Egypt
well guys after those negative comments how we can calculate the resisor for the LED??in that case

Joined:
Jul 1, 2011
Messages:
334
Likes:
21
Location:
Earth
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. ### ericgibbsWell-Known MemberMost Helpful Member

Joined:
Jan 4, 2007
Messages:
21,238
Likes:
645
Location:
Ex Yorks' Hants UK

Joined:
May 26, 2012
Messages:
26
Likes:
0
Location:
Cairo-Egypt
19. ### flintyNew Member

Joined:
May 26, 2012
Messages:
26
Likes:
0
Location:
Cairo-Egypt
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.

Joined:
Oct 27, 2006
Messages:
14,047
Likes:
141
Location:
Rochester, US
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. ### flintyNew Member

Joined:
May 26, 2012
Messages:
26
Likes:
0
Location:
Cairo-Egypt
that was pretty but if the current value exceed Maximum Permissable LED current Limit milli-amps??
what is gonna happen ??