# Noob question about parallel LEDs

Hi All,

I'm in the process of creating a sculpture, I have started to learn Arduino thanks to all of the substantial documentation online. I'm trying to figure out how to light multiple LEDs from one pin on the Arduino.

I'm kind of stuck, I've been looking online and every tutorial explains that I need another chip that can handle multiple LEDs.

Is it possible to daisy chain multiple LEDs or parallel wire them with one pin controlling the brightness with PWM?

Eventually what I want to do is have the LEDs dim in and out, in a circular arrangement.

yes you can run more than one led (maybe two max depending on the leds) from the same pin either series or parallel.

You need to think about how many leds, what voltage, and current you need. If it's dozens of leds or 100's of ma it will just be simpler to use separate drivers.

Eventually what I want to do is have the LEDs dim in and out, in a circular arrangement.

That part is a little confusing. If you wish for each and every LED to fade at a different time, then you can't use a series or parallel arrangement, but rather need a I/O pin for each LED, or external logic circuitry. If they can all turn on and then fade out at the same time then you can use series or parallel arrangements.

The method to use series or parallel wired LEDs depends on the external voltage and current capacity you have available, if any. Without external DC power, on the Arduino, can really only wire them is parallel using +5vdc available at one of the connectors and with enough current available for maybe 25 or so, However you will have to use a switching transistor to control the parallel array of LED's. The Arduino I/O pin would turn on (or PWM on/off) the transistor which will then turn on the high current path for the parallel LEDs. Each LED would also require a current limiting resistor to hold it's current draw to 20ma or less.

If you are new to electronics it is better to copy an existing design and wiring example. A little searching should turn up something.

Lefty

Do not wire LEDs directly in parallel, because they will not share the current evenly and you will most likely get variations in brightness from one LED to the next. Use one current-limiting resistor per LED.

ok how does one indirectly wire led's in parallel ?

how does one indirectly wire led's in parallel ?

By having an LED and resistor in series and wiring that LED / resistor combination in parallel.

There is no need to put an apostrophe on led's, in this case you are referring to many LEDs not anything possessed by the LED. For example you can say the LED's lead because that is the lead of the LED but for many diodes it is simply LEDs
rant over

its just an odd term

(and yea I am one of those who is bad with the ')

Some of us think you can use an apostrophe for plurals of abbreviations to aid clarity (otherwise the "s" can look like part of the abbreviation).

Andrew

If you want to run multiple LEDs in parallel from a single pin, then a) do as Mike said (ie, parallel rails with the current limit resistor and LED combos in parallel) and b) above a certain number of LEDs, you will need to connect them to a driver of some sort, either a high-power transistor or MOSFET, with the string of LEDs connected to the output of that. This will allow your arduino to drive the driver with its lower current capability, and the driver transistor/MOSFET can handle the extra current needed by all of the LEDs. Just like driving a motor.

That part is a little confusing. If you wish for each and every LED to fade at a different time, then you can't use a series or parallel arrangement, but rather need a I/O pin for each LED, or external logic circuitry. If they can all turn on and then fade out at the same time then you can use series or parallel arrangements.

Sorry for the confusion - the circle of LEDs will all go on and off at the same time, I am hoping to control this with one pin, because there is a larger part of the sculpture that I'd like to free up pins for.

An image of what I am talking about, all the LEDs would be in this pattern and would turn on and off with PWM:

Do not wire LEDs directly in parallel, because they will not share the current evenly and you will most likely get variations in brightness from one LED to the next. Use one current-limiting resistor per LED.

Thanks, I'm going to try that.