LEDs for Beginners

Step 9 Extrapolation

While I didn't actually end up making anything besides a couple of lit LEDs, this information can be used to make all kinds of cool things!

The take away concepts hopefully were:
- Power a whole bunch of different value LEDs using the same basic principals.

- Figure out what is the positive electrode and what is the negative electrode of an LED by looking at it and testing it.

- Use resistors, or combinations of resistors wired together in series or in parallel to supply the correct amount of power to the LED.

- Make calculations to determine what resistor is needed using the formula, or using web sites that do it for you.

- Wire LEDs in series or in parallel depending on the application.

- Make LEDs light up!

This was the most basic kind of walk through for LEDs possible - and I learned a whole lot along the way. LED arrays and wiring schemes can get significantly more complicated - but for the most part, LEDs are pretty simple to work with, and with relatively little knowledge I was able to light them up - all be it if I sent a little too much juice through them towards the end of the experiment. I don't fear the LED now. They are my friends.

Comments

[lmccoy]

Thanks for the tutorial! This is great - it's helped so much!

[Welch76]

If I'm planning to make a series of LEDs...let's say 12 2.1v LEDs. How many resistors do I need and what voltage. (I am so sorry, I'm lost here.) Thanks for the help.

[imarzouka]

Here is a good LED calculator that I use to find the resistor values i need for my LEDs

http://ledcalculator.net

[t.rohner]

12 x 2.1V=25.2V is the voltage to light them up hooked up in serie, so 27V or 3 x 9V batteries in serie makes sense as a supply. To get the resistor value: (27V-25.2V)/0.02A=90 Ohms. To calculate the power dissipation over the resistor, multiply the voltage times the current. (1.8V x 0.02A=0.036W so 1/8W type resistors are overly sufficient) I don't know all the available values by heart anymore, but at least i'm sure 47 Ohm is available in the cheap 5 and 10% tolerance carbon film series. Now you only have to hook up 2 of them in series to get 94 Ohms, which is precise enough. (especially given their tolerance and the LED's threshold voltage tolerance)
Or you hook them up parallel to 3 V with a 47 Ohm resistor to each Led. These Led's will drain your batteries with 240mA, so if you want them to stay on for a while, take "thick" batteries.

[Welch76]

Oh gosh, I love you tons. Thanks so much for the help. I'll share the image IF I do manage to make it happen hahaha. Thanks again. :D

[aservantofhis]

I need 805 leds wired together. the specs give different voltages i dnt know whats what. they are 0.5w each. it says this: Reverse Voltage: 5.0 V but also says DC Forward Voltage: Typical: 3.4 V Max: 3.8 V and it also says DC Forward Current: 100mA. if they are .5w and current is 100mA then the voltage would be the Reverse voltage figure, 5 volts so whats the other voltages for? If i wired in series i would need 5volts * 805 which is 4025v !!!i dont think so. So ill wire them in parallel but i dont want to wire a resistor to each one. what other options do i have? cant it just work if i wire them in parallel to a 5v 400w supply without resistors?

[knight2067]

The forward voltage is the one you want. The information I got about my high brightness one was 3.3-3.6v forward and max 5v reverse. It worked with about 3.5 but if I put 5 volts through it, it would burn very quickly.

[DarkStar851]

Reverse current = Adaptors or USB current.
Forward current = Batteries, or any form of DC current.

It's just different types of electricity. :]

[knight2067]

What I mean was you do not want to use 5v on a LED. I was saying it could not be the reverse one because it was too high. Anyway, the reverse voltage/current is the voltage/current that goes through the LED in the wrong direction (negative/cathode to positive/anode). If it goes over the max, you'll have a useless piece of plastic, metal and semiconductor.

Wikipedia (on semiconductor diodes):

At very large reverse bias, beyond the peak inverse voltage or PIV, a process called reverse breakdown occurs which causes a large increase in current that usually damages the device permanently.

Also from Wikipedia (on diodes):

The most common function of a diode is to allow an electric current to pass in one direction (called the forward biased condition) and to block it in the opposite direction (the reverse biased condition).

The reverse voltage is the PIV.

If you use AC at a low voltage (below 4v), the LCD will flash, turning on when the current is going through it the right way (forward bias) and off when it goes the wrong way (reverse bias).

[stagebuilder]

I have a question related to this article. I have a 20 LED string of battery powered Xmas type lites, running off of a 3xAA battery pack. Within the battery pack is a single resistor, which appears to be 5.1 ohms (green/brown/gold/gold). I want to splice another length of 20 LEDs onto the exiting set but run all 40 off of the same 3xAA configuration. Do I just divide the resistor value in half since I doubled the load (work being done) ?

[doughnutty]

I am looking for this answer also.

[legomitch02]

i think you would need the same resistor because they both have 4.5v going to them and they both need a smaller voltage so you would have to lower the voltage of both using the resistor

WARNING: this may be worrng wait until someone else confirms this  ty ^^

[brittomonier]

Though I have little knowledge ( or nothing ) about LEDs, the way you walked me through in explaining all the wirings both in series and parallel was really really excellent and very much interesting and thank you so much my friend.

[legomitch02]

Im following the Music LED Light Box instructable and im using a 12v power supply with it. Is it possible for me to have a connection made from the power supply to an ipod speaker that runs on 3.6v using resistors?

[vknutt]

Cheers for this one mate... it's a fantastic starting point!

[xxninjanickxx69]

wow this is was such great tut
i have been tryin to figure this out for
awhile now i can go wire my leds in my
xbox 360

[osirisbrackhaus]

Great instructional, took a lot of reluctance off my hands. Thanks a ton!

[Lotsafish]

Thanks man, this is a lot of help, I'm just starting out working with LEDS and your guide is a great starting point.

[Blue Dingo]

Great explaination of LED operation. Now I can light up my (Burning Man) Playa Bike like the 4th of July!

[wiiman07]

Love this Instructable I recently made a plexiglass pyramid with one led inside I wish I had known this then I collative wired a whole bunch together in a parallel circuit and made it so much cooler

[grizzly g]

thank you! one of the best instructables ive seen...

[Ceddy17]

Thx, I needed this. BTW, I have loose LED's in a toolbox lying around. How can I determine what voltage they are?

[un0]

Using a multimeter and ohm's law you can determine the values of the LED.

Using the multimeter to measure the voltage of the LED. Most of the time, LED's have a amperage rating of 20mA, so the LED runs on (your number here)volts @ 20mA.

How to calculate the resistor needed?

r = (Power supply voltage - LED) divided by the 20 mA (0.02)

[Nickelplate]

Thank you so much! This is exactly the kind of basic information I needed!

[dyerb2009]

Great article. Just to make you aware, you can find LEDs on-line at electronics distibutors. Allied, DigiKey, etc. Sometimes when you need 1-5 LEDs, you can request samples - not free, but better than buying a 250+ minimum. High power LEDs (350 mA to 700 mA) can also be purchased on star boards. These are convenient to mount to a board and easy to wire. Great for flashlights. In the power LED department, the Vf (forward voltage) typically runs from 3.3 V to 4.0 V, depending on the color and type.

[cvdude20]

i wish u can help me make an iron man arc reactor

[narf]

i probably know even less about LEDs than anyone here, i found this very helpful though. i was wondering if it would work with less bulky batteries, such as the button cell ones? i have a pre-made set of LED x-mas lights that i want to convert from using 3 AA batteries to using something a lot smaller...it already looks like it has a resistor, so theoretically if i switched out the batteries with something of the same or less voltage, it should work?

[Istarian]

The issue is not the type of battery, but it's voltage and amperage. Button and coin cells are both small in relation to AAs. Most also have a lower amperage, such as 1,200mAH or much less like 300mAH. If it were 1,200mA it would last for 1 hr at a maximum current draw of 1,200mA or differently depending on certain formulas and the current draw. So whether you can use them depends on the leds voltage and how long you want it to last. Lets say you have a 20 led string, and the leds have say a 2v power rating then you would need a resistor (100ohm/220ohm should be fine) and one or two of the said batteries (assuming a 3V 1,200mAH rating on them). A lot of leds run on 20mA average. Therefore the example I suggested would run for 3 hrs. maybe a little more on a 3V 1,200mAH since it's more than 2V (ie. 20mAx20=400mA, 1,200mAH/400mA=3 hrs.).

[jafrance]

Can you expand a bit more on this? This is something I am really curious about in setting up a really simple project I want to build (basically a garbage can light since my 3 yr old likes to throw things away that he shouldn't). I want it to last as long as possible. What things do I need to know/look for?

[maxattenborough]

Thanks very much for your post it was exactly what I needed, I've been excited about led projects for a while but not got round to it because it felt a bit out of my depth regarding the formulas etc. you explained it very well and now I'm going to build some great stuff! Thanks again

[Bionex]

Thanks! this was a really helpful instructable. Im adding it to my favorites for future refrence <(spelling?)

[Eddiev1985]

Thank you very much!!! Before I found this instructable, I knew nothing about LEDs or how to make them light up. At 42 years old, I am just now becoming interested in electronics. So I decided to self educate. Thank God for the internet, and people like you wanting to share thier knowlage and experience with anyone with a desire to learn something new. Good job! Eddiev1985

[kathrynl]

Thanks for taking the time to explain that. There are so many projects that I want to do involving LEDs, and understanding this better really boosted my confidence about getting them done and done correctly. : )

[IRQ_VET]

Question does this concept work the same for infrared LED's as well?

[lemonshark10]

yes

[tave]

im just wondering what the differance would be between these two A) if i put the resistors in series (right after the batteries at the positive end)before the parallel circuit began or B) if i put the resistors right before the LED in the parallel circuit

[PearlZenith]

Thanks for taking the time to write all this out. I always feel stupid when my dad explains these things to me, so seeing it really helps cement the knowledge in my brain.

[ranaakamarth]

Thanks a tonne ive also found out how much fun electronics can be (although confusing and headachey at some points). But i'm a nerd... who is the best soccor player in our league... Soldering owns (and hurts!)

[Eliriel]

Thank you for the instructional. I'm finding that I'm wanting to begin experimenting with electronics more and more... I did a small mod on my Robosapien involving a volume switch and discovered I absolutely loved to solder. Anywho, thanks again! 'Twas very interesting! :)

[tonsofhoopla]

Nice Instrucable, the Resistor lesson also came in handy, thank you!