LEDs for Beginners

This instructable shows how to wire up one or more LEDs in a in a basic and clear way. Never done any work before with LEDs and don't know how to use them? Its ok, neither have I.

***If you have wired up LEDs before, this explanation might seem overly simplistic. Consider yourself warned.***

Step 1 Get some LEDs

So I wasn't completely honest - I have used LEDs once or twice before for simple applications, but I never really knew what I was doing, and since so many projects on instructables use LEDs, I thought I might as well teach myself and post about it too.

I know that there are many projects already posted that contain information about how to wire LEDs for simple projects - LED Throwies, LED Beginner Project: Part 2 and 9v LED flashlight - teh best evarrr!, but I think that there could still be some use for a detailed step by step explanation about the basics of LEDs for anyone who could use it.

The first step was to buy some supplies and figure out what I would need to experiment with. For this project I ended up going to Radioshack because its close and a lot of people have access to it - but be warned their prices are really high for this kind of stuff and there are all kinds of low cost places to buy LEDs online.

To light up an LED you need at the very minimum the LED itself and a power supply. From what I have read from other LED instructables wiring in a resistor is almost always a good idea.

If you want to learn about what these materials are check out these wikipedia entries:
LEDs
Power supply
Resistors

Materials:

LEDs - I basically just reached into the drawer at Radioshack and pulled out anything that wasn't more than $1 or $2 per LED. I got:

2760307 5mm Red LED 1.7 V
2760351 5MM Yellow LED 2.1 V
2760036 Flasher Red LED 5 V
2760041 2 Pack Red LED 2.6 V
2760086 Jumbo Red LED 2.4V

Power Supply - I really didn't know what I would need to power them so I bought some 9V batteries and some 1.5V AA's. I figured that would allow me to mix and match and make enough different voltage combinations to make something light up - or at least burn those little suckers out in a puff of smelly plastic smoke.

Resistors - Again, I wasn't too sure what I would need in terms of resistors here either. Since I got a whole bunch of different LEDs with various voltages I knew that I would need a couple different types of resistors, so I just bought a variety pack of 1/2 Watt Carbon Film Resistors (2710306).

I gathered up a soldering gun, solder, needle nose pliers, electrical pliers, some primary wire and electrical tape too since I thought they might be useful.

Comments

[jnajmy]

Thanks for the instructions, but i do not get some parts.

For my project I am going to us a 9 volt battery and have 20 LEDs and each LED has a voltage of 3.2-3.4V at 20 mA each. I want to run every LED in a parallel circuit.

How would I go about doing this? What size resistors would i need? I bought 1/4 watt resistors could i use those? or would i need to get a 1/2, 1/4, 1/8, ect.?

Also do i need to have 20 different resistors for each LED or could i just use one at the bottom of the parallel circuit?

Do I have to keep in mine about anything else? I would be using a 9 volt 1000+ mAh battery

Thank you in advance!!!

[dgarside1]

Thanks! Very useful instructable, I can recommend using a solderless breadboard though, much less soldering involved!

[babylonfive]

The two big reasons why you place a resistor in series with each LED are: - safety - so that if one LED burns out (becomes an open) the remaining LED would use twice the current (overcurrent) and then fail as well - so that the current and brightness will be somewhat equalized Imagine a situation with two LEDs of the same type but a sightly different forward voltage at the specific current - or think of it really as a curve of current over forward voltage. Then, because one LED uses more current for the same forward voltage, it's brighter... sometimes by a lot. Finally, when the battery voltage falls, the higher forward voltage LED winks out. David

[smartteez]

Hi, Just surfing looking for some help - not done electronics since school 28 years ago. Looking to link 100 leds in parralel to a 12 volt leaisure battery. this is the spec for the LED's off ebay - with them being 12v does this mean I don't need any resistors in? Also is there much heat generated looking to set them in to an MDF panel.

Thanks in anticipation

Prewired 12V LEDs

High quality LED, soldered to a resistor for 12V (including 12V automotive) use. Strong connections are neatly wrapped with heat shrink and attached to colour coded wire terminating in stripped tinned connections.
Technical Spec

High Power 3mm LEDs - 7000mcd

12V DC
Presoldered Resistor

20 mA
20 cm Wire Length
High Intensity - Low Power 0.36W

Simple to Use
Long Life and Energy Saving

[babylonfive]

So, if you use these LEDs with built-in resistors, you are golden. All the variation in voltage of the LEDs is equalized by the series resistor selected to properly drive each one. So, even multiple colors on the same bus will work as expected.

You can do it like this:

+12 ------------------------------------------------------------------
| |
R R
| | o o o as many as you like
led led
| |
gnd ------------------------------------------------------------------

Concerns:

- multiply the current per LED (shown on the specs for each LED, above you say it is .020A) times the number you want (100?) = 2A. Therefore get a power supply that can provide 12V for at least 2A (more is ok). Repeat this formula if the current is different to determine the max ps current needed.

- I wouldn't group a big pile of these RIGHT TOGETHER of in a confined space. Each dissipates .36W (almost all in the resistor), so three or four tightly together (or out of air flow) will be a watt of power, and will start getting a little hot. For this issue, a much better solution would be to create your own LED 'cluster' of series LEDs and a single resistor setting the voltage. If you created 33 sets of three LEDs on the same line with a single custom resistor value to limit to 20mA, then your power dissipation would go way down. This is because the power would go toward light instead of being boiled away in the resistor - resistors just waste!

So this:

12V+ ------- led ------- led ------- led ------- resistor ------- gnd

3.2V 3.2V 3.2V 12v-9.6=2.4V
2.4V /.020A = 120ohms
2.4V x .020A = .048W

Note this dissipates lots less in the resistor. and there are only 33 resistors instead of 100. it uses the voltage much better.

But if you can easily get air to these guys, you'll be fine.

[smartteez]

Thanks I think I'll look at the 2nd option as these are to be enclosed in a shallow box in the roof of my camper and I don't fancy setting it on fire. Cheers

[justaj]

So if you add a resistor in series with each LED, does the resistor have to be the full value? So for example he used two 100ohm resistors in series above. If he did what you said, would it be a 200ohm resistor for each? My guess would be yes but I am new to this.

[babylonfive]

No, you would use the same working configuration for a single leg or multiple legs, up to the limit of the power supply.
So: in your example above you have a 5V supply, and an LED that uses 20mA at 3V, then the voltage 'left over' across the resistor on any one leg is 2V. 2V/100ohms = .020A (20mA). Thus each leg would correctly function with a 100ohm resistor.
Each leg draws the 20mA as a separate subsystem, as it's own circuit. You should see it as if the + point in the drawing above were two independent batteries. The only limitation would be the maximum current available at the + point... remember that mA are thousandths of Amps, so a power supply rated 1A @ 5V would provide enough power for 50 LEDs... 50 x .020A (20mA) = 1A... batteries can do much better than 1A without much voltage reduction.

I hope this helps you think about this in a way that allows you work with LEDs and resistors in the future. Please reply with any questions or comments.

[14cooldude]

I'm making a color organ and each of the three panels has 100 leds on it. So what is the voltage, current, and resistor value needed to light 100 and 300 leds?

[babylonfive]

What's your desired power supply value? Do you have a 12v supply? The components wl be different for each color. Also holler back with how you are controlling the leds... Pulse width modulation? Variable voltage output? Let me know.

[justaj]

Thanks for your reply!

Sorry I wasn't clear. I was referring to step 8 where he used the 9V and wired the two LEDs in parallel.

R = (9V - 1.7V) / .04A
R = 182.5 Ohms

So in that case it would be a 200ohm resistor for each correct?

[babylonfive]

If you mean about 200 ohms (i.e. 180 ohms) on each leg, then yes. In fact, up to the limit the 9V battery will source, you can keep adding legs with an LED and a resistor; it'll keep adding current, and reducing battery life obviously. Two will use 80mA, 3 will use .12A etc.

[sfrazier2]

It seem you know a lot about led i'm looking to go to led on my reef aquarium to save energy and money I have now metal halide total 500 watts. the heat is crazy hot and the light bill is through the roof, what would you recommend for a 60"x10" strip

[Fireson13]

Can this be modified to flash?

[dean14111]

if you put a capacitor in it........i think - im kinda new to this LED stuff.

[dean14111]

you have the best instructions on builing a LED project. im just a beginner asfar as LED'S go and you REALLY helped me out so thank you!!!!

[4lifenerdfighter]

If the battery is 1.5 volts and the led has a voltage drop of 1.7 volts, then how is it lighting? Am I unaware of something?

[Tzoul]

Thank You! Would you solve my problem? I am using a 14.8v power source to light 16 bi-colored leds in a parallel. I understand I need 32 Resistors, but what strength? My led specs are like this: 2.9v draw, 25mA, Please help. When I enter this into the many resistor calculators Ive found on the web, they give me such incredible resistor suggestions, however I wonder if this accounts for each led. Another thing I can not rap my mind around is that: occasionally I will have both colors on at the same time. How do I figure that into all this resistor calculatiing. The leds are three pronged 5mm, thank you in advance instructables!

[Berrydueds]

I have trouble with my Leds, The schematics are below.
My problem is that the middle row of Leds always gets burnt out.
The first time I didnt use any resistors and the middle row completely burnt out but the rest were fine.

Second time, I only had 470ohms 1/4W resistors. Same issue - the middle row burnt out.

Also, i only have 470ohms resistors, if i used the right amount (100 ohms ) would this solve my problem?

[daspoint]

Missing one piece of info here -- what is the forward voltage of the LED ? ( this is sometimes related to what colour the LED is --- range between 1.5 v ( Ultra violet) to as high as 3.4 volts ( bright white ) per LED. ) I guestimated 2.5 volts each for your circuit here which should work out to 330 ohms 1/4 watt. One thing you need to remember -- This will work ONLY if all the LED's are the same type and colour. If you use different colours, the math becomes a bit more fun.

Why the middle row "burns up" ? One or more of your LED's is faulty ( "open" or of a different type ) or the resistor in that row can't handle the power ( too small in watts such as 1/8 or 1/16th of a watt value ( also "opened" - look for the new all dark brown colour band )) AND -- If you try to reuse an LED that you already burnt up, It may continue to act as a "open" in the redesigned circuit. Test each LED with a 1.5 v battery before reuse. I use a 9 volt battery with a 220 resistor in series to test all my LEDs.

Finally , 470 ohms should work just fine. ( see note above about using "open" LEDs)

[ziccy64]

I'd like to know how to power a "flashing LED".Can I use Ohms law and power it that way.I have some which are rated as 3.6v at 30ma.I have some 6volt batteries(remote control little ones).Thus Ohms law states that the resistor should be 80 ohms.Can I do it simply that way or is there something which I left out?
Thanks

[makerbuilderbaker]

Finding the resistor is an application of ohms law.
Don't go to an online calculator, you should learn it as it is simpler and more effective than an online source.
V=IR (Voltage = Current times Resistance)
if the supply voltage is 5 the forward voltage is 2.5 and the forward current is 25 mA or .025 amps.
R=V/I so R= (5-2.5)/.025 so R=2.5/.025 which is 100 ohms. It is simple to use and more effective than an online calculator. There is a good site that explains this:
http://cuttingedgescienceclub.blogspot.com/2012/01/ohms-law-practice-problems.html
scroll down to the section labeled LED problems or you can look at the earlier sections to help.

Always figure out the forward voltage (how many volts it eats up/needs to run) the forward current (the optimal amount of current that it wants) and the voltage supply you have.

[sokamiwohali]

so i have a question...if i wanted to take a single led and rig it to use from 1.5v to up to a 12v power supply, what resistor would i want to use?

[askjerry]

Do the math... if you know that an LED runs at 1.5 v and that it uses 0.020 amps (20mA) then you just use ohm's law.

12v (power) - 1.5v (LED voltage) = 10.5 too much voltage.

If the LED runs at 20ma... then 10.5v / 0.020 = 525 ohms... or about 560 ohms. (Standard resistor value.)

But most LEDs I have seen use 2.2 to 3.4 volts... so run the math with those numbers.

[sokamiwohali]

tyhe only problem is that i am not for certain what the running voltage is on the led i am using. its the assorted pack of led's from radioshack, and the package says not what the voltage is of any of the led's.

Thank you for the reply tho. i am new to the whole LED thing, and i am currently working on a 4 LED USB tester that involves bi-directional current...basically it tests for proper polarity, as well as proper wiring (ie data NOT hooked to power, and power not hooked to data as well as wether or not both are wires backwards). i just finished soldering it together, but none of the led's are working...i know its in the way i designed it somehow...

[askjerry]

Well this should help... at least it will get you in the ballpark.

http://www.ledtronics.com/html/ColorChart.htm

[sko56]

The only reason the LED doesn't Fry from adding 1.5V is because the Alkaline Battery has an internal resistance. Ohms Law Holds true I (current) = V(volts)/R(resistance in Ω) . If there was no resistance the current would be near Infinity causing the Wattage to go through the roof as well (W=I^2*R). same reason a "throwie" works without a resistor.

[damadtatter]

How do you make an ohm's symbol on a keyboard?

[JustinPayne]

The easiest way, in Windows, is by bringing up charmap, scrolling down the list until you find the "&" symbol, copy it, and then paste it into the window.
You can also hold down the ALT key and type the decimal value of the character but wasn't successful getting the character to print out. My guess is it has something to do with the character map I was using. In any case, I think using charmap is probably the best way to print non-keyboard generated character.

[aasteveo]

For Mac, just press Option+Z.

[thankey]

In Word or Excel make change the font to "Symbol" and then hold the 'alt' key while typeing 89 on the numeric pad. Or use the Insert” tab, click W, and then choose the symbol you want.

[ydeardorff]

I'm trying to build an array using 2.0 vdc 15K MCD 4 post LED's.
My smaller array is fed by a 12vdc 150mA power supply using 20 LED's hooked in parallel. they hooked up using 510 ohm resistors.
I had 4 burn out while handling the unit. was this because of something I did wrong?
Im building tail lights for a custom car. so they will be fed by the cars 12 volt system.

Any help?

[PlattinumPanther]

you want to calculate 12-14VDC for an auto application as the only time you should get 12VDC is when the generator isn't running

[cyber.engineer]

Check your speck for Vd and Imax calculate using my equations below. LEDs in Parallel will not always be the "exact" same brightness. However if you put them in series one burns out they all fail if it goes open if it shorts your other LEDs get brighter and have a lower life. If it were me, I would use one resistor per each LED and quit using them in parallel. That is just a personal like. www.brainpwr.com

[sdanks]

Most LEDs want about 18 milliamps of current. So 12v/.018A = 666.67 ohms. I would use about a 680 ohm resistor in line with the LED. That would make them last longer. Max is usually around 20 mA. You were sending 23 mA through them. So just change to around a 680 ohm resistor or whatever the standard resistor value is that is cheap around that value.

[cyber.engineer]

Sdanks you are in error you must drop 2 volts and make it 10 for your equation so it will be 10V/.018A and most that I use are 20ma. some are much more and the Vd (Voltage drop is higher) www.brainpwr.com sorry, an Electrical Engineer here with 30 years experience

[sdanks]

I was just trying to help the guy that didnt know anything about electronics. But since you are an electrical engineer, lets be more accurate. Silicon voltage drop across a junction is actually .6 -.7 volts. So , 12V - .6 = 11.4 Take 11.4 volts and divide it by .018 and you get 633.33 ohms. SO, a 680 ohm resistor would work out good. 20 mA is usually Ic max with most LEDS wanting around 18 mA typical. a 680 ohm resistor would work really well. I stand by my initial statement. Different LEDS have different typical current requirements, but even at your calculations, 10/.02 = 500 ohms and he burned up 4 leds at 510 ohms, so I would STILL recommend he use 680 ohms resistors.

[pgheit01]

The charging circuit of a car typically puts out 13.6V, so 13 / 0.018 = 722.222. Sorry, but I don't know what the common size resistor is to exceed that rating. Also, the power is kinda noisy, so I'd think about transients. At the least, I would put a meter to the socket with the engine running and see what I get. Maybe even take readings at idle and with a friend stepping on the gas a little. Good luck!

[chungmatthew]

HI for some reason when i connect my copper wires to the LED light it doesnt light up but it lights when i connect with out the wire. I been trying to extend then wire so i can connect it to somewhere feather away but it doesnt work can anyone tell me what i have done wrong or what i could do better ?

[lmccoy]

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