Picture of Flicker up to 6 LEDs with Arduino
Hi there.
Christmas is coming closer, and I was wondering if I could put some candles in my room to get in the "christmas mood".
But after a friends house burned down of christmas tree candles, I don't want to burn real candles into my room.
So why don't let the Arduino light for you?!

This Instructable will show you, how to flicker up to 6 LEDs using an Arduino Microcontroller.
For more information about Arduino visit

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Step 1: What you need...

Here are the things you will need:

-Arduino Microcontroller (or similar)
-USB cable
-LEDs (up to 6 LEDs are possible)
-Resistors (equal to the number of used LEDs)

LED resistor calculator

if you don't want to solder the circuit:
-Jumper wires

-DC power source

-Arduino IDE
Get it here!

-TrueRandom Library
Get it here! (Instructions included)
Unzip it to your "Libraries" folder.

Step 2: Wire it up!

Connect the resistor to the PWM pins (e.g. 6, 9...) on the Arduino board.
Now connect the second "leg" of the resistor to the anode of the LED (long "leg")
Then connect the cathode (short "leg") of the LED to ground (GND) on the Arduino board.

Repeat this step for each LED you want to use.

When the wiring is done, continue to the next step!

Step 3: Code it!

Copy this code to the Arduino IDE:

//Multiple LED flicker by gotcha (2010)
  <TrueRandom.h>   //Include the TrueRandom Library

int ledPin1 = 9; //Set the number of LEDs you use.
int ledPin2 = 10;
int ledPin3 = 11;
int ledPin4 = 6;
//You can use up to 6 LED pins

void setup()
pinMode(ledPin1, OUTPUT); //Sets the LED pins as output pins.
pinMode(ledPin2, OUTPUT); //Use the same pins used above
pinMode(ledPin3, OUTPUT);
pinMode(ledPin4, OUTPUT);

void loop()
{ //Sets a random value of LED voltage in the range of 0V - 5V with PWM
analogWrite(ledPin1, TrueRandom.random(0,255)); //Use the same pins used above
analogWrite(ledPin2, TrueRandom.random(0,255));
analogWrite(ledPin3, TrueRandom.random(0,255));
analogWrite(ledPin4, TrueRandom.random(0,255));
delay(TrueRandom.random(40,70)); //Limits the speed.

I like very much ! Thank you and Happy Holidays !
hds04052 years ago
Great project, simple to implement and just perfect for the application I needed (inside a carved Halloween pumpkin display for my son). Thank you!!!
phatguppy2 years ago
This was a great starter tutorial and introduction to Arduino. I'd like to slow down the randomness in the blinking, to make it look more like fire flies. Any suggestions on how to tweak the TrueRandom library to do this?
Hey phatguppy.

After reading this instructable and looking at the code it looks as if the delay between flickers comes from the written code instead of the library.

In the line 'delay(TrueRandom.random(40,70)); //Limits the speed.'

I believe the '(40,70)' are ms. It's setting a range for time between flickers. Change them for a longer delay.
ledfreak012 years ago
this i awesome keep it up
gotcha99 (author) 3 years ago

thanks for the infromtation,but somehow i can't add the needed lines in the instructable.

For those wanting to use the code: put " "
after "#include"
CODIY3 years ago
Hi Gotcha,

Great little script. I am planning to use it to drive lights on a wreath. I noticed that you left out the library name in your include statement.

For those looking to duplicate this code, note that you need to download and install the TrueRandom library into your Arduino folders, then complete the include statement in the script as follows:


the library can be found here: