How to Make a String of LED's in Parallel for Arduino





Introduction: How to Make a String of LED's in Parallel for Arduino

About: I play varsity ice hockey as a goalie, and enjoy making stuff in my free time. I built a 3D printer a few years ago, and I like to create Arduino-based electronics projects. I have somewhat of an aversion to...

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!

Step 1: 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

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

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

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.

Step 5: LIGHT IT UP!!!

As the title says, LIGHT IT UP!!!!!!!!!!!

Plug it into your arduino and start programming.



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    Thats series. Not parallel. Parallel would allow you to lite them individually.

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


    5 replies

    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.

    You can use a shift register like a 74HC595 to address 8 LEDS individually using 2 pins. You can daisy chain shift registers to run even more off of only 2 pins but your limited by the amount current you can provide. You can provide a separate power supply for the shift registers to provide adaquate current and if you do it's a good idea to make a common ground with the Arduino.

    I have a way to control 2^n leds with n pins, for exemple if you have 16 leds, you can encode a binary number with 4 bits and use a decoder to convert it to decimal and turn on the specific led at the speciefed position (0101 will turn on the 6th led (because 0000 is the 1st)). But you can just turn on 1 led at a time or few of them by switching very fastly between them so they will blink as fast as it can't seeable by eyes!

    I do! I do :D

    you can use the way keyboard recogonizes keys, i forgot what it's called but also monitors do the same thing, did you think they have a billion pins ? :D

    you can also do the same thing ws2812 LEDs do (check neopixel)

    You can use a led matrix and shift registers to control several leds with a 2 pin. Technica is called Multiplexion

    Don't you need an individual Resistor for each of these? otherwise they get weird, one might turn on at full brightness and the other might not turn on at all!

    and the source code???

    do you know wich amount of led max can be put in linear?

    1 reply

    I'd like to know this too. Thanks for this instructable!

    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.

    What type of wire did you use and how do you connect the wire to the arduino?

    See my projects for some other ideas! ;-D


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    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!)


    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.

    3 replies

    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.

    Okay, I'll make a note that this method works best with small strings of LEDs.