How to make a string of LED's in parallel for arduino

Picture of How to make a string of LED's in parallel for arduino
This instructable will show you how to make your own string of LED's that are wired in parallel. The arduino board can't supply enough power to run a string of LED's in series without a relay or transistor, but it can run one that is wired in parallel. It takes a little more time and effort, but it works great!
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Step 1: Materials

Picture of Materials

Wire (2 colors)
Soldering iron
Meter stick or yard stick
Knife (a flat carving knife works well)
Wire cutters
Battery pack for arduino (helpful but not required)

Step 2: Prepare your LED's

Picture of Prepare your LED's
If you have clear LED's, program a code onto your arduino that keeps an LED on, and plug in each one to make sure it works and is the right color.

Even if you don't have clear LED's, you might want to bend your wires out a little so you don't accidentally solder them together.

Put some solder on each lead. This helps a lot later.

Step 3: Prepare your wires

Picture of Prepare your wires

Stretch out both wires on your working surface next to your meter stick or yard stick. Tape the ends down so the wires stay straight.

Now, decide how far apart you want your LED's to be. Use your knife to cut a notch in the plastic insulation at each interval.

Put some solder into each notch. most of the solder should be sucked into the wire.

Step 4: Put it together

Picture of Put it together

Just heat it up!

Hold an LED so the lead is touching the bare wire in the notch. Make sure that the short lead is on the ground wire and the long lead is on the other wire. Use the soldering iron to melt the solder on the LED and wire. Some of the solder that was sucked into the wire should come back out onto the lead, which helps strengthen the bond.

Repeat for each LED on both wires. You should end up with a string of LED's somewhat like the one in the second picture, but not wavy. I bent the wires to test the string in a project that I am working on, then unbent them for the picture.

akellyirl2 years ago
It's best to add a resistor in series with the string to limit the current. With many LEDS in parallel without a resistor it's pretty much guaranteed that you will over-stress the pin and destroy the Microcontroller. On the other hand, adding a resistor will make the LEDs disappointingly dim. The answer is to use a Relay or Transistor to drive the string.
jjacobson22 years ago
What type of wire did you use and how do you connect the wire to the arduino?
D3v45t4t0r3 years ago
do you know wich amount of led max can be put in linear?
pandyaketan3 years ago
See my projects for some other ideas! ;-D


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philspitler3 years ago
I presume that these LEDs are either all on or all off. Or, are they individually addressable?


Goalieguy (author)  philspitler3 years ago
That is correct. If you want to control each LED individually then you need to connect each one to a different pin on your microcontroller. As far as I know, that is the only way to control each one separately. If you or anyone else reading this comment knows a way to control multiple LED's individually with a single pin, I would love to know about it.
jimthree3 years ago
To be fair, I have to agree with Russ on this, You should touch the voltage regulator, or the main Atmel chip on the arduino, if either feel slightly warm, you are risking damaging your hardware. I'm no expert on this, I'm pretty noob myself with electronics, but I don't think you really need a current limiting resistor on each LED (although that would be best practice for sure), but I wouldn't run this without at least one resistor in series (and it doesn't have to be a big one!)

My understanding is that LED's essentially behave as a short circuit. They don't have any internal resistance of their own. Left to their own devices, they would pull as much current as the supply could provide, to the point (and then beyond) they need to burn themselves out. As Russ said, it's only the internal wiring and components of the arduino that is saving them here. Current Limiting Resistor, the clue is in the name :)

Lovely Idea though, I've been doing the same with 4core alarm wire and RGB leds (and huge amounts of hotglue for insulation!)


pyanystyul3 years ago
russ_hensel3 years ago
This is not a good idea without some modifications.

1) The port has a max current as well as max voltage, current is usually around 20 ma ( see the spec sheet ).

2) You need a current limiting resistor for each led.

Yes it may work, but will stress the arduino and perhaps the LED's. A low side transistor for a switch is a much better way to go.
Goalieguy (author)  russ_hensel3 years ago
I am a beginner with arduino, so thank you for the input.

I actually did some research on this and found a post on a forum that you can have up to a couple hundred LEDs on one string if they are wired in parallel, because each one takes such a small amount of current. Also, I meant for this instructable to be a guide on how to wire LEDs in parallel quickly. I also wanted to spark ideas for projects that can be made using this. I am currently working on using twelve strings of eight LEDs to make an LED pumpkin.

Anyway, thanks for the input and for posting the first comment. If I can get some more information on the arduino's limits, I will make a note in the instructable about it.

I would be interested in a link to the post, I think it is very wrong. Led's used to be run at about 20 ma per led. The super bright mder ones have ( i think ) about this as max current and will be visible at about 1ma. As LEDs are current controlled devices they often do not play well ( share current ) in a parallel circuit.

You circuit relies on the intrinsic current limiting of the port, this is not good for it.
Goalieguy (author)  russ_hensel3 years ago
Okay, I'll make a note that this method works best with small strings of LEDs.