LEDs for Beginners








Step 1: Get Some LEDs





Power supply



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




Step 2: The LED

LEDs come in different sizes, brightnesses, voltages, colors and beam patterns, but the selection at Radioshack is pretty small and so I just picked up a couple different LEDs from what they had in a few different brightnesses and voltages. I kept close track of what LED was what voltage because I didn't want to accidentally send too much current through one of the low voltage LEDs.

The first thing I did with the LEDs was figure out which wire (its called an electrode) was positive and which was negative. Generally speaking the longer wire is the positive electrode and the shorter wire is the negative electrode.

You can also take a look inside the LED itself and see whats going on. The smaller of the metal pieces inside the LED connects to the positive electrode and the bigger one is the negative electrode (see picture below). But be warned - in the LEDs I picked up I didn't always find this to be true and some of the LEDs had the longer electrode on the negative when it should be on the positive. Go figure - its OK though, if it didn't light up I just flipped it around.

Once I knew what was positive and what was negative I just had to remember what the voltage of each LED was.

All my LEDs recommended 20mA of current. 20mA is standard for most LEDs.

Step 3: Power Supply

To make the power supplies I just soldered some wire onto the ends of the batteries I had bought so that I could easily attach the LEDs to them. The 9V battery served as my 9V power supply, one AA battery made a 1.5V power supply and three AA batteries bundled together made a 4.5V (1.5V + 1.5V + 1.5V = 4.5V) power supply. I didn't use alligator clips on the ends of the wire, but they would have been helpful here.

Step 4: Resistors

I opened up the assortment pack to find that resistors aren't labeled with what value they are. The pack said it contained a whole bunch of different resistors from 100 ohms to 1 Meg ohm so I set out to see what was what. When I poked around online I found that all resistors have a coding system on them that tells you what value they are.

Here are two pages which explain in depth about how to calculate resistor values.

Do it yourself
Have it done for you

I'll go through the examples of how I calculated the values myself in the next few steps when I start wiring up my LEDs.

For the time being I just admired their little colored stripes and moved on to trying to get just one LED to light up.

Step 5: One LED, No Resistor

I thought that I would start as simply as I possibly could - just one LED with no resistor. First I had to decide what power source to use and which LED to light up. This may seem obvious, but this was my first time through so I might as well be as clear as possible...

LEDs require sufficient voltage to light them. Sometimes if you give them too little voltage they wont light at all, other times they will just shine dimly with low voltage. Too much voltage is bad and can burn out the LED instantaneously.

So ideally you would like the voltage of the LED to match the voltage of your power supply, or even be slightly less. To do this you can do a couple of things: change your power supply voltage, change the LED your using, or you can use a resistor that allows you use a higher voltage power supply with a lower voltage LED.

For now I just wanted to get one lit up so I chose my the power supply that had the lowest voltage - the single AA battery which outputs 1.5V.

I chose to light the red 1.7V LED since the battery outputs 1.5V and I knew I wouldn't kill the LED with too much power.

I wrapped my positive wire from the battery to the positive electrode of the LED and wrapped the negative wire from the battery to my negative electrode and presto - let there be LED light!

This first experiment was pretty easy to do - just some wire twisting and enough knowledge to know that the 1.5V power supply would light the 1.7V LED without need a resistor.

Step 6: One LED With a Resistor

It was just a coincidence that I bought an LED that was 1.7V and that it ended up working being able to be powered by my 1.5V power supply without the use of a resistor. For this second setup I decided to use the same LED, but up my power supply to the three AA batteries wired together which output 4.5V - enough power to burn out my 1.7V LED, so I would have to use a resistor.

To figure out which resistor to use I used the formula:
R = (V1 - V2) / I

V1 = power supply voltage
V2 = LED voltage
I = LED current (usually 20mA which is .02A)

Now there are lots of calculators online that will do this for you - and many other instructables reference this as a good one, however, the math really isn't too hard and so I wanted to go through the calculation myself and understand whats going on.

Again, my LED is 1.7V, it takes 20mA (which is .02 A) of current and my supply is 4.5V. So the math is...

R = (4.5V - 1.7V) / .02 A
R = 140 ohms

Once I knew that I needed a resistor of 140 ohms to get the correct amount of voltage to the LED I looked into my assortment package of resistors to see if I could find the right one.

Knowing the value of a resistor requires reading the code from the color bands on the resistor itself. The package didn't come with a 140 ohm resistor but it did come with a 150 ohm one. Its always better to use the next closest value resistor greater than what you calculated. Using a lower value could burn out your LED.

To figure out the color code you basically break down the first two digits of the resistor value, use the third digit to multiply the first two by and then assign the fourth digit as an indicator of tolerance. That sounds a lot more difficult than it really is.

Using the color to number secret decoder website found here, a 150ohm resistor should have the following color code...

Brown because the first digit in the value resistor I needed is 1
Green because the fifth digit is 5
Brown because in order to get to 150 you have to add one 0 to 15 to get to 150.
Gold - the resistors I got all have 5% tolerance and 5% is represented by gold

Check out the decoder page link above if this isn't making sense.

I looked through all the resistors, found the one that was brown, green, brown, gold, and wired it in line on the positive electrode of the LED. (Whenever using a resistor on an LED it should get placed before the LED on the positive electrode).

Low and behold, the LED lit up once again. The 150 ohm resistor stopped enough of the 4.5V power supply from reaching the 1.7V LED that it lit up safely and kept it from burning out.

This is just the process that I went through to figure out what resistor to use with my particular LED with my particular power supply. You can easily use the formula above to figure out what value resistor to use with whatever LED and power source you happen to be using.

Step 7: Wiring Up Multiple LEDs in Series





R = (9V - 5.2V) / .02A
R = 190 Ohms
Next higher resistance value - 200 Ohms







Step 8: Wiring Up Multiple LEDs in Parallel

Unlike LEDs that are wired in series, LEDs wired in parallel use one wire to connect all the positive electrodes of the LEDs your using to the positive wire of the power supply and use another wire to connect all the negative electrodes of the LEDs your using to the negative wire of the power supply. Wiring things in parallel has some distinct advantages over wiring things in series.

If you wire a whole bunch of LEDs in parallel rather than dividing the power supplied to them between them, they all share it. So, a 12V battery wired to four 3V LEDs in series would distribute 3V to each of the LEDs. But that same 12V battery wired to four 3V LEDs in parallel would deliver the full 12V to each LED - enough to burn out the LEDs for sure!

Wiring LEDs in parallel allows many LEDs to share just one low voltage power supply. We could take those same four 3V LEDs and wire them in parallel to a smaller power supply, say two AA batteries putting out a total of 3V and each of the LEDs would get the 3V they need.


And finally, just some warnings...wiring in parallel drains your power supply faster than wiring things in series because they end up drawing more current from the power supply. It also only works if all the LEDs you are using have exactly the same power specifications. Do NOT mix and match different types/colors of LEDs when wiring in parallel.

OK, now onto to actually doing the thing.

I decided to do two different parallel setups.

The first one I tried was as simple as it could be - just two 1.7V LEDs wired in parallel to a single 1.5V AA battery. I connected the two positive electrodes on the LEDs to the positive wire coming from the battery and connected the two negative electrodes on the LEDs to the negative wire coming from the battery. The 1.7V LEDs didn't require a resistor because the 1.5V coming from the battery was enough to light the LED, but not more than the LEDs voltage - so there was no risk of burning it out. (This set up is not pictured)

Both of the 1.7V LEDs were lit by the 1.5V power supply, but remember, the were drawing more current from the battery and would thus make the battery drain faster. If there were more LEDs connected to the battery, they would draw even more current from the battery and drain it even faster.

For the second setup, I decided to put everything I had learned together and wire the two LEDs in parallel to my 9V power supply - certainly too much juice for the LEDs alone so I would have to use a resistor for sure.

To figure out what value I should use I went back to the trusty formula - but since they were wired in parallel there is a slight change to the formula when it comes to the current - I.

R = (V1 - V2) / I

V1 = supply voltage
V2 = LED voltage
I = LED current (we had been using 20 mA in our other calculations but since wiring LEDs in parallel draws more current I had to multiply the current that one LED draws by the total number of LEDs I was using. 20 mA x 2 = 40 mA, or .04A.

And my values for the formula this time were:

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

Again, since the variety pack didn't come with that exact value resistor I attempted to use the two 100 Ohm resistors bundled together in series to make 200 Ohms of resistance. I ended up just repeating the mistake that I made in the last step again though, and wired them together in parallel by mistake and so the two 100 Ohm resistors only ended up providing 50 Ohms of resistance. Again, these LEDs were particularly forgiving of my mistake - and now I have learned a valuable lesson about wiring resistors in series and in parallel.

One last note about wiring LEDs in parallel - while I put my resistor in front of both LEDs it is recommended that you put a resistor in front of each LED. This is the safer better way to wire LEDs in parallel with resistors - and also ensures that you don't make the mistake that I did accidentally.

The 1.7V LEDs connected to the 9V battery lit up - and my small adventure into LED land was completed.

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.

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852 Discussions


Tip 5 weeks ago

Need a SUPER QUICK Flashlight and happen to have some Vape Mod Batteries laying around? Batteries used in Vape Mods are 3.7 volts and most of the common LEDs, 5mm and 3mm ones that I come across anyway in all kinds of gadgets and small Lamps and Flashlights. I also got 100 of them on Ebay for less than $5. This isn't fancy but like I said it's quick and couldn't be any more simple, a small piece of wire, an LED Bulb, or Diode, a couple of pieces of tape, and the Battery and that's it. You can even get away with just one SMALL piece of wire just long enough to connect either post to one end of the Battery so that you can still reach the other end of the Battery with the second post. I just bend the post to lay flat on the terminal and then put a piece of tape across it as well as the wire on the other end. And BAM! Instant, and little, but bright Flashlight and the 18650 Batteries last forever when using a little LED and they're rechargeable. I have a couple of them scattered around the house in places you wouldn't have multiple Flashlights stashed , like closet's and drawers. I've replaced all of my AA and AAA Battery hog Electronics that I own with 18650's. And without any resisters or anything, as long as they're compatible.


6 weeks ago on Step 9

Thank You for the refresher course...It fitted perfectly with what I neede to know..Yes it was "simple" but in my view simple works every time ..THANKS again


Question 3 months ago

I want to connect 5 smd 12volt in parallel , according to manufacturer each need 12 volt and 1.7 amps . I want to use ac 220 volt power supply as well as 12 volt dc battery with 6.7 amps. Please guide me about power source will 12 volt 10 amps amps work good. Does any other adjustment except beat sink required to lightup

Chukwudi Emmanuel

5 months ago

Please,which resistor that can resist 12v to power this 28 LED white connected in parallel


Answer 6 months ago

Do you mean the breadboard? You can get a breadboard from Amazon.


Question 7 months ago

Can you power 3 LEDs in series with 2 or 3 AAA batteries?


Tip 7 months ago on Step 6

When you look at an LED from the top one of the sides has a small flat spot, that indicates the negative (ground) side. This is helpful when reusing LEDs that have had their leads cut.


8 months ago on Step 9

Hi I`m new to electronics too and despite the comments from mr. grumpy I enjoyed the article and have a greater understanding of LEDs. and resistances, good on ya feller,

I loved it. and like you I have made some errors but that how we learn. John Page.

Haripriyaa M

Question 10 months ago on Step 6

Here it needs 140ohm resistor.Can I use a 1kohm resistor?


Question 11 months ago

Is there IC which makes 2 LEDs light up mutually?


Question 11 months ago

Is there IC which makes 2 LEDs light up mutually?


2 years ago


2 replies

Reply 1 year ago

I did a similar project many years ago, before I had any electronics training. It worked, but I was puzzled about some of the behaviors. The issue is that putting a bunch of LEDs in parallel, without individual LEDs will work well, only if each LED has at the same voltage drop. If one of the LEDs have a lower voltage drop, they will steal more current from the others, so that it is prone to failure.

If you read the LED's specs from the manufacturer, they will give the voltage drop as a range. Perhaps for a green LED 2.7v to 3.4v. In your parallel circuit, with only one resistor, that 2.7v odd-ball one is going to be brighter, draw more than its share of the current, and die a quicker death.

The author of the article has done an in interesting job of learning through experimentation, but he failed to uncover certain details. I think the biggest mistake was that he is treating a LED like it was a incandescant bulb. The 2nd error is in thinking that this "no resistor" circuit actually did not have a resistor. In fact, there was some small resistance in his battery. As long as the battery is fairly small, and the voltage is just a little below the voltage drop of the LED, it may work.


Reply 2 years ago




Grumpy Mike

1 year ago

You said at the start:-


So what makes you think it is OK to perpetuate the myths you have here?

You always need a way to control the current with LEDs, and the simplest way is a resistor. The no resistor circuits shown here uses the internal impedance of your battery to limit the current, if you use another type of battery you can start a fire or have an exploding LED. It is irresponsible of you not to point this out as it could be a danger.

If you try and wire LEDs in parallel without a resistor for each LED, they will not share the current evenly and you will damage them. Look at your own picture and you can see they are not the same brightness.

2 replies

1 year ago

Radio shack? How old is this?