This is a pretty simple project that makes a cool, flickering led star! Perfect for the holidays!

Time needed: A few hours

Complexity: Low

Cost: For materials, <$5, for arduino board: around $30

Skills needed: Soldering

Step 1: Materials!

This is a very simple project and only requires a few parts.

1x Arduino. Anything from an ATTiny to an UNO will work, as long as you have the means to program it. This will not work with a Mega. Sorry!

LED's, any color (preferably yellow/orange ish. Any color will do though). You will need 30-50, depending on how big/what shape you want your star. The LED's I got were clipped short, so it was harder to solder.

Perfboard. I used an 70x90mm sheet.

Wire

Soldering tools (soldering iron, wire strippers, helping hands etc)

Step 2: Arrange LED's

I decided to arrange my LEDs in a classic, 4 pointed star shape (Star of Bethlehem).
It is the basic shape of this:

You can do any shape you want here, just remember, the more complex it it, the harder it will be to solder. Also, make sure to arrange your leds in a way that will make sense. Make SURE your LEDs are arranged in the correct polarity throughout the project! Otherwise, it will be very confusing and you may have LED's that wont work!

Step 3: Tape Down LED's

Once you have arranged your LED's the way you want, use tape to secure them to the perfboard. You have to do this unless you want to solder the LEDs in one by one.

Step 4: Mark Your Paths

This is something I neglected to do with my board. I highly recommend you try it. Just use a sharpie or something to mark the side if the LEDs that will be hooked together, and do it for the other side with a different color. Because I didn't do this, my leds were soldered down wrong, and I had to re-do a lot of the board. Attached is a crudely drawn image of what my LEDs might have been marked like:

Step 5: SOLDER!

Bend the legs of the LEDs so that they all connect together in parallel. Solder everything together.This step takes the longest time. Test every few minutes to make sure you don't have any shorts. Double check the leds before you solder. You might need to have some wire jumpers near the points of the project. I had to do this.
Solder 2 wires onto the + and - leads of the led's. These will go to the Arduino

Step 6: Get the Arduino Library.

For this project, I used the TrueRandom library: you can download it here
There are also instructions here for how to put the library in the Arduino Software

Step 7: Code the Ardunio

Open the Arduino software and start a new Skech. Insert this code
#include *TrueRandom.h* void setup(){ } void loop(){ analogWrite(9, TrueRandom.random(0,255)); delay(10); }
Replace the *'s with < and >, and upload it to the arduino. Plug the positive wire of the star into pin 9 of the arduino, and the negative wire to ground. The display should light up and "flicker". That's it! All done. In my project, note that I have not used the center LEDs yet. I am using them for something else :)

Thanks user oweng4000 for the code! Also, many thanks to user Robot Lover, for putting on the advent calendar, and doing such a great job on it. How about a quart of oil for the Robot, huh? Cheers!