Introduction: 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:
Power supply


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.

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

Now that I knew how to wire one LED with various combinations of LED voltages and power supplies, it was time to explore how to light up multiple LEDs. When it comes to wiring more than one LED to a power supply there are two options. The first option is to wire them in series and the second is to wire them in parallel.

To see an in depth explanation about the difference between series and parallel check out this page. I'm going to cover wiring LEDs in series first.

LEDs wired in series are connected end to end (the negative electrode of the first LED connects to the positive electrode of the second LED and the negative electrode of the second LED connects to the positive electrode of the third LED and so on and so on...). The main advantage of wiring things in series is that it distributes the total voltage of the power source between all of the LEDs. What that means is that if I had a 12V car battery, I could power 4, 3V LEDs (attaching a resistor to each of them). Hypothetically this could also work to power 12, 1V LEDs; 6, 2V LEDs; or even 1 12V LED if such a thing existed.

Ok, let's try wiring 2, 2.6V LEDs in series to the 9V power supply and run through the math.

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

Now the variety package of resistors didn't come with a 190 or 200 Ohm resistor, but it did come with other resistors which I could use to make a 200 Ohm resistor. Just like LEDs, resistors can be wired together in either series or parallel (see next step for an explanation on wiring things together in parallel).

When same value resistors are wired together in series you add their resistance. When same value resistors are wired together in parallel you divide the value of the resistor by the number of resistors wired together.

So, in the most simplified sense, two 100 Ohm resistors wired together in series will equal 1 200 Ohm resistor (100 + 100 = 200). Two 100 Ohm resistors wired together in parallel will equal one 50 Ohm resistor (100 / 2 = 50).

Unfortunately, I learned this key point after I wired my resistors together for the experiment. I had originally wanted to wire two 100 Ohm resistors together to equal the 200 Ohms of resistance I needed to protect my LEDs. Instead of wiring them in series, as it should have been, I wired my resistors in parallel (did I mention I am beginner with resistors?) So my resistors were only providing 50 Ohms of resistance - which apparently worked out OK on my LEDs in the short duration of the experiment. Having too much power getting to the LEDs would probably burn them out in the long term. (Thanks beanwaur and shark500 for pointing this out.)

I took my resistors and placed them in front of the positive lead of the first LED that was wired in series and hooked them up to the battery and once again, there was LED light!

With three different combinations of LEDs and battery power supplies and no puffs of plastic smoke yet things were looking good - aside from my little confusion between wiring resistors in series and in parallel.

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.

In short, wiring in series divides the total power supply between the LEDs. Wiring them in parallel means that each LED will receive the total voltage that the power supply is outputting.

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.


MichaelM1219 made it!(author)2017-03-22

Thank you for such a clear description of LED's and resisters. I didn't have a clue what all those stripey things were on the various circuit boards of things I took apart (sometimes being nosy, others thinking I could actually do something to fix whatever it was that didn't work) I shall now go forth with my new found knowledge and start taking even more things apart and see if I can get them back together before finally breaking them and throwing them in the trash. At least I will now be breaking them with a little bit of knowledge (who said a little bit of knowledge was dangerous?). Watch-out household electrical items I am coming for you, yes you you little radio and you thought you were too smart for me, ha ha well get ready to meet your breaker!

darrennie made it!(author)2017-07-13

MichaelM1219 watch out for Capacitors, they can pack a real shock if they are not discharged.

KaylaB50 made it!(author)2017-02-11

I didn't have a breadboard or whatever it's called. My Soldering iron came in the mail so I wanted to make something to practice with until the rest of my parts for my real project came. I stopped by 2 different radio shacks looking for the regular small leds in white but none of them had them so I used a big white one and 3 small red ones. Got 2 3x AAA battery holders some resistors, some button's, and some wire. Through trial and error burning my fingers a few times, accidentally almost blowing up the batteries, I got the lights to turn on. Figured it was time to solder. Learned on the tiny buttons, I had wired the 3 leds in series, skipped the resistors as I figured splitting it 3 ways shouldn't fry the leds. The jumbo led I had gotten some info about while at radio shack and he told me I wouldn't need resistors. Soldered them, and they worked! The buttons only turn the light off if I hold them so those are probably the wrong buttons. But they were so tiny and cute for my little altoids tin light.

devicemodder made it!(author)2017-06-12

you soldered it across the battery. when the switch is pushed, the battery is shorted. the way the switch is soldered, the longer side is connected internally. you'd want to solder the switch like this...
red wire and led positive to switch, led negative to one side of a resistor and the battery negative to the other side of the resistor.

briancejdj made it!(author)2017-05-28

I have a quick question, If I have a board with a 3V LED in it and I throw in a 5V led in its place, will this ruin anything on the board or just not properly light the LED as bright as it could be? Wasn't sure if the LED would try and pull 5V on a 3V slot and burn anything out., thanks!

Tomas+Meyer made it!(author)2017-03-01

I learnt this the hard way when a year or so ago, I bought some flashy new UV LEDs and put them in parallel to make a lamp, then watched them all fr

Jake+Maverick made it!(author)2017-02-28


thanks for this instructable but i have a related question....i have numerous LEDs powered by a 9 volt battery....trouble is it's draining the battery way too part of the circuit i just added is a separate circuit board that makes the LEDs breath/ fade up/ fade those LEDs did not light at all, although the others in the circuit did....until i changed the battery then all worked as it i can only conclude that the battery is draining too quickly on this circuit...having to change every couple of days on ittermittent use. i suspect it's a Q of soemthing i need to do with the switch...but only way to wire a switch is as a circuit breaker on the +ve wire....? i know i have had this problem on 3volt circuit before....just can't remember what i did to fix it! :-(

Rouke made it!(author)2017-02-25

Thank you very much for these instructions.

I'm using LEDs with a forward current of 20mA and a peak forward current of 120 mA (Conditions: ulse width less than 10 msec and duty less than 1/10). How much more light will the LEDs emit with increasing current (so long as the conditions aren't exceeded)?

chuckr44 made it!(author)2017-01-01

Thanks! I'm tryinig to look for a tutorial using an LED with a 3 position slide switch, OFF-ON-ON. So the first ON would be a bright light and the second a dim light. But I've been searching google for 2 hours and can't find anything with a 3 position slide switch. Can you make a tut about that? Thanks again! :)

steve.rand made it!(author)2017-02-09

If you have your three positions, I imagine there would be two pins for the two "on" positions, in which case you could wire the led to both pins, but use a different value resistor for each, and the negative can come in on the common "input" pin.
I imagine the switch would break the circuit when it's off, join the circuit to pin1 at one position, then cut that and join the circuit to pin2. If it's a sliding thing and there is a chance that pin1 and pin2 can be bridged while the switch is sliding, I guess you'd have two inputs with two resistors in parallel which reduces the resistance and could overdrive the LED. There is probably a way around that or you could make sure the sliding switch (brass spring contact type) has a large enough separation that it never contacts pin1 and pin2 simultaneously.

OmarG87 made it!(author)2017-01-14

this might help you a bit. its 48 white led's powered by 9-12volts and its superbright with no resistors.

LeoT44 made it!(author)2017-01-17

Hey, just a quick question, your "stand" or holder for the LEDs where can you get these?

WilliamB360 made it!(author)2017-02-01

I have a small string of "fairy lights" LED's that are powered by two CR2032 batteries wired in series producing 6.2 volts (measured). I wanted more capacity so I connected the LED light string to 4 AA batteries wired in series producing 6.25 volts (measured). The 4 AA batteries burn out the LED string. Why?

steve.rand made it!(author)2017-02-09

Any additional voltage will change the formula, so it's possible that you are letting the LEDs draw too much current, which burns them out. It's also possible that for cheapness' sake, there is no resistor on your fairy lights as lithium batteries tend to have a very low discharge rate which is probably just right for the LED's, but now you have AA's which can dump way more current, that this is what has burnt them out.

edenecke made it!(author)2017-01-25

You can mix colors in parallel if you calculate the correct resistor for the gnd side. E.g. A red with a small resistor and a green with a larger resistor. If it's dead on they'll have the same brightness as well.

smithjoe115 made it!(author)2016-12-28

Hi, I currently have 10 solar powered decking lights with each
consisting of 3 leds running off a 1.2v AAA rechargable 600mah
batteries. I would like to replace the solar power as its unpredictable
with a power supply. Could i simply connected all 10 lights in series
which would require a 12v power supply? What current/amps should is use as of course i have no spec sheet for the leds? TIA

smithjoe115 made it!(author)2016-12-28

Would i need a 12v led driver power supply at 600mA = 7.2w - i have found a 12v - 500mA would this be sufficient? if used the a 12v - 833mA led driver power supply would this be too much as i read the LED Driver power supply is more efficient? TIA

HernanM22 made it!(author)2016-12-14

Hi. I have 2 LED lamps that they are 6V each. How can I connect them to a 12V source? Just connect them in series?


ZacharyV11 made it!(author)2016-12-09

I have a question, I am setting up 83 LEDs in series in my car, I want to put this in my tail light and use the same lights for running lights and brake lights. The orginal bulb has a three prong plug, two 12v sources and a ground in the middle. I want to run the LED's at 9v until it gets the second signal from the brake line then to run it at 12v. I would love any help I can get, and if I should post this elsewhere????

excessnet made it!(author)2016-12-13

Use a Relay to switch from 9V to 12V when applying brakes. (You'll have IN-A 9V, IN-B 12V and the IN-B will also activate the Relay).

On the "daylight" wire, just add an LM7809 to get 9V Output.

You might also want to add a capacitor the the output of the relay to prevent the light from closing / opening everything you apply the brakes.

MohamedE358 made it!(author)2016-12-06


red+scruffy+442 made it!(author)2016-12-05

ur lights are cool

el74588 made it!(author)2016-11-21

wow I can't believe you did this ! It seemed so hard to me!

Kootenayboy made it!(author)2016-05-31

I hope I may ask a question, I have a led light that I recycled from a spot lamp that packed it in. the original unit was 6volt but I do not have a 6 volt power source I do however have a 9 volt one. is there a way to use this power source for that led pack? or would I burn them out. I have basic knowledge of electronics but Im unclear on how much these lights would draw if they would take what they need and disregard the rest

AaronK73 made it!(author)2016-07-05

There's a circuit called a voltage divider. It's made by placing two resistors in series, then connecting a wire to the center of this series. Look it up, perform calculations to figure out which resistors will split the voltage into 6V, and use it.

Kootenayboy made it!(author)2016-11-21

awesome thank you, since I posted this I ordered some LEDs and protptype boards from china the LEDs came with a bunch of resisters and thanks to your reply I now know what they are for lol :)

JamesW440 made it!(author)2016-11-18

Nothing wrong with a voltage divider circuit. There is also a thing called a voltage regulator that will do an astounding job at maintaining the voltage at whatever it is designed to produce. Some have built-in adjustability. Others are set voltage like LM7805 which is a 5 vdc version (and inexpensive), so you would need to find a 6 vdc version. In fact there might even be one built into the device, but I doubt it. If so, it might handle 9 vdc.

And, no, they won't take what they need and disregard the rest. It depends on what is in the package that runs the device at 6 vdc. If it has a regulator or a voltage divider that somehow handles the 9 vdc, you will have lucked out. Otherwise, you have toasted it most likely.

JimW123 made it!(author)2016-05-31

I preface this with, my dad was an electrician and I wanted nothing to do with his long drawn-out lectures on the theory of electricity when i was a kid....

I'm helping my son with a project. His assignment was to build a 3-story building with 7 rooms. Each room has to have 2 lights and an independent switch but all seven rooms have to be powered by one power source. We bought these battery powered tea lights that come with a CR2032 battery and removed the battery ( and then soldered pairs of two in series (7 pairs in total). I can't find any specifications for the lights as far as voltage so the only information I have is what a CR2032 battery provides. These only have to stay powered for a few minutes while the teacher gives the structure an "earthquake resistance test". Any help or ideas on an appropriate power source?

JamesW440 made it!(author)2016-11-18

I suspect that your situation is long since passed, but I think a single 3 vdc 2032 would run all of these lights if hooked in parallel. In other words, the two lights should have been wired in parallel, not series. I am assuming that these are LED lights.

Place all of the switches where they will be located in your model. Once the switches are in place, wire the battery plus (+) to each switch. I am assuming that your switches are only going to 'break' the plus (+) line.

Start with a wire that runs to the nearest room from where you want to place the battery. Run the wire from the battery plus (+) to the switch and then from there to the next nearest room's switch and so on until all seven switches are connected on their input side. (It might be easier to connect all of the first floor on one line and then all of the second floor on another line, but that part doesn't matter.)

When all of the switches are connected on the plus side, connect the lights in each room to the plus (+) side of each light and then to the other side of the switch it will be operated by. None of these light connections should go to any other switch - just the switch in that room and NOT to the battery minus (-).

Now all of the minus (-) side connections of the parallel lights should be run to all of the other minus (-) connections so that all of the minus (-) side connections are together and attached to the battery (-).

One CR2032 should run all of it and the switches should control each independently.

Now I suspect that there is a reason for wanting to wire the house and then show a resulting fault that an earth quake or something like that would have on the wiring as the house falls. You might want to wire each switch directly from the battery plus (+) to avoid a portion of the house falling from taking the power away from the rest of the house. You could run the plus(+) and the minus(-) together to each switch, etc. Perhaps the young man knows what the teacher is trying to achieve so that you can route your wires accordingly.

vu2aeo made it!(author)2015-08-30

"Once I knew that I needed a resistor of 140 ohms to get the correct amount of voltage to the LED"

I think you mean to say that the resistor ensures that the CURRENT flowing through the circuit does not exceed LED's CURRENT rating of 20 mA. In your previous step...if you had an LED rated at 1.5 volts and you used a 1.5 volt battery WITHOUT a resistor, your applied voltage would be perfect but you would burn out the LED since the current flowing through it would be extremely large.

RafaelN13 made it!(author)2016-02-02

I understood your post and like to ask you something:

If ideally we had a 1.7v input, a 1.7v led that consumes 20ma, which resistor you would need to securely feed the led?

JamesW440 made it!(author)2016-11-18

The situation here is what resistor do you use when the LED and the voltage source are the same? What should be done to overcome the 'no resistor needed' situation? You can approach it by increasing the supply to a higher value or look at the spec sheet to find out just where 1.7 v is and where 20 ma is with regard to the device specs. If the 20 ma is the optimum operational current for the diode, then design to that current. If the light output doesn't change appreciably, try using a lower voltage. That is, suppose the diode works ok at 1.5 vdc at 20 ma. 1.7 - 1.5 = 0.2 v. At 20 ma the resistor in series with the diode would have to be 0.2/0.02 = 10 ohms. That would work, but the resistor really should be larger, so it would be better to up the source voltage if you can. The 10 ohm resistor is better than none.

vu2aeo made it!(author)2016-02-09

So you need to ensure that only 20mA flows through your LED correct? What size of resistor would permit only 20mA to flow when a voltage of 1.7V is connected across its leads? R = V/I, so R = 1.7 V/ 20 mA = 85 Ohm.

So 85 Ohms is the resistor you need, choose the closest available resistor higher or equal to this value.

AaronK73 made it!(author)2016-07-05

This isn't quite correct... 1.7V(in)-1.7V(f)=0V, 0V/0.02A=0 Ohms. It should be fine without a resistor, though a resistor won't hurt if your voltage source has potential to spike.

QJ+Neo made it!(author)2015-09-01

I thought that the LED itself can control the current passed through it when the applied voltage doesn't exceed its forward voltage? My teacher told me resistor only needed when the applied voltage exceed the forward voltage of the LED.

JamesW440 made it!(author)2016-11-18

But isn't that always the case? If not, the LED would not work.

JamesW440 made it!(author)2016-11-18

I disagree. He stated it correctly. He was designing so that at the current spec'ed the voltage would be at the right amount as seen by the diode.

And I think you are incorrect in the second one, too. If the diode is rated at its forward voltage to accept 20 ma when 1.5 vdc is applied, then the current that should be flowing with that battery hooked without a resistor is 20 ma, not extremely large. Unless, of course, the real 20 ma current spec is for a 1.2 vdc supply, then the current might get higher, but not an awful lot - though probably enough to destroy the LED

The only thing about not having a resistor is that the power might fluctuate (usually in battery-operated situations that is not a problem) such as arcing in the line caused by poor contact, when a power supply gets hit by a transient it can't handle or an automobile starts up charging its battery at 14.3 rather than 12 vdc. These are the reasons to not leave out the resistor.

RafaelN13 made it!(author)2016-02-02

I understood your post and like to ask you something:

If ideally we had a 1.7v input, a 1.7v led that consumes 20ma, which resistor you would need to securely feed the led?

JohnP479 made it!(author)2016-08-04

I'm a bit confused. I decided to find out why cheap LED torches pop their LED's. Not a resistor in sight. 7 white LED's on 3 rechargeable 1.2 V batteries still pop. They are all wired in parallel. The article states how to connect LED's in parallel with one resistor and further on someone states each LED in parallel must have it's own LED. It does seem that should an LED pop the load on the others will go up if only one resistor is used therefore it would be a good idea to run them at a slightly lower current than maximum. Should an LED pop then the current would still be within tolerance and the batteries / LED's would last longer. The light would degrade slightly though.

JamesW440 made it!(author)2016-11-18

It is not that each LED 'must' have its own resistor, it is just less problems if they do. LEDs will still 'pop' because they fail. Not knowing what the spec sheet says, one is running a fairly large risk of failure if the current gets too high. These diodes are only tested for operation not longevity.

If you put one resistance (combo of resistors or just one) in series with each diode, the effects of one 'popping' is not noticed by the others. And the problem goes up linearly with the number of LEDs sharing a resistor.

If you look at the spec sheets, there is a range of values where the light output is relatively constant. The design point should be near the downward curve of the output and further from the max where it will 'pop'.

CarlosC187 made it!(author)2016-02-28

I need to make lamp battery 3,7V it should be commanded by a momentary switch

1click 1 led on, 2nd click 2 led on, 3rd click off.
Anyone can help me?

LiamB41 made it!(author)2016-05-30

I don't understand why people recommend microcontrollers. It's stupid and a waste of money, just get a small electrical switch and solder the power cable to it. Doesn't get much simpler than that.
Not sure if these switches are toggle or hold:

JamesW440 made it!(author)2016-11-18

I think the main reason that they recommend them is that they understand them. It takes more than hooking wires together to make it work. Would you guys please explain how you get this microcontroller to do anything at all? I think that you have to write a program, don't you? And don't you have to understand how to write that program into the controller as well? Can you modify the program when you find it doesn't work?

Don't get me wrong because I think you are right. But we tend to go with what we know. This might all be fun for you, but not so much for someone who doesn't have the knowledge or inclination to attempt it.

And another thing, I worked on a tractor that had an instrument panel operating off ordinary electric gauges. It had broken and for $200 the people who owned the tractor replaced it with one that uses a microcontroller. It worked for awhile and then broke again. I looked at both the old one and the newer one and found that the old one was still operable, but I could get nowhere with the newer one because I couldn't find any specs on the microcontroller. I fixed the problem with the original analog panel and it works fine. (BTW, the problem was that the ammeter in both units overheated and burned things up. (There is no connection between the ammeter and the other gauges except proximity.) I could find no reason for the overheating so I took the ammeter out, tied its input and output wires together outside of the instrument panel and replaced it with a cute little digital voltmeter. No problem since.)

Dizzdogg made it!(author)2016-09-14

The microcontroller provides a reliable/stable current/voltage control than a simple resistor, and also provides more possibilities such as: pattern flashers, and transmission of data. Led's connected to microcontrollers can also be used as testing equipment.

sifu-dianji made it!(author)2016-08-04

microcontrollers can easily do what weeks of analog or IC design would struggle with. at £3 a pop for a arduino nano with 13 io ports, ic2, 8 analog ports, serial connections and 6 PWM lines, which will also run many other functions, why not? otherwise, you end up with a huge horrible mess of ANDs, 555s, 4017s, ORs, capacitors, NANDs, resistors, diodes and wires ect. whilst trying in vain to find that ONE dry joint in a million connections- I've been there, and digital is easier trust me.

AaronK73 made it!(author)2016-07-05

A microcontroller with 4 outputs can go for as little as 50 cents (if you have the software/hardware to upload). Here's an example[] without microcontrollers. You can also build toggles using simple circuits like JK Flipflops, or buy toggle switches.

sifu-dianji made it!(author)2016-08-04

so, the most easy way would likely be a microcontroller, but you could (if you're willing to settle for a toggle/slider) just use a single pole triple throw switch:

one lead unconnected, the other two linked by a diode and each two a LED. both other ends of the LED to ground via an appropriate diode each, and the switch's communicator to +3.7v.

or if you like a challege and are rich, you could use latching AND gates, a NOT gate and a triple pole momentary switch but unless you have custom pcb tools and surface mount soldering gear, it will end up massive. also, trying to describe it with ascii charactors will be near impossible

a slider may also be more easy to use tho

Kiragacash95 made it!(author)2016-03-20

You're probably better off going to an electrical shop (a decent one) and talking to a member of staff

Karim+A.K made it!(author)2016-02-28

Youre gonna have to use a microcontroller for that, an arduino should do

MikeB385 made it!(author)2016-06-30

Ok, let me see if I've got this straight.

I want to do 50 LEDs in parallel. They're all 3v, 20mA. Assume they're all pretty well matched.

If I wanted to use a 5V power supply, and just use 1 resistor, my math would look like this:

50 * .02A = 1A (total current)

R = (5Vpower supply - 3Vload) / 1A

R = 2V / 1A

R = 2Ω

Also, 3V * 1A = 3Watts,

so I would need a 3W 2Ω resistor, correct?

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