If you make the star legs watertight with silicon sealant, the star can easily be attached to an outside wall, door or fence.
The power supply to the Nano is 5V DC.
You can use a long 3-wire cable between the Nano and the Xmas star to keep the electronics mounted inside and the star outside.
Or mount the Nano in a small box close to the star and power the nano with 5V.
The programming can be altered to make the light effects behaviour any way you like.
You need to print 5 star points, feed the LEDs through them and then have the wires come out somewhere. You can glue the points together with hotglue or transparent silicone sealant after assembly and testing.
Solder the 3 wires of the WS2812 LED string to the Arduino Nano (5V to 5V, Gnd to Gnd and the Data IN of the LED string to D3 of the Arduino Nano. That’s it! After that you can connect the Arduino to your PC with a data USB cable and download the code from my website.
If you don’t have the Arduino IDE yet, download the app from the Microsoft website (Arduino IDE).
Make sure you download my Arduino code and open it with the Arduino IDE APP> Probably the APP will have to move the arduino INO file to a new directory but that should do the trick. If not, do it yourself.
In the Arduino IDE select the right microprocessor (Arduino Nano). Then select the correct processor version (large or small memory) and the old or new bootloader. These choices depend on the type of Nano you bought or still had lying around. Then you choose the right port (USB) for your Nano.
To test if you have connection between IDE and Nano , you can ask if the Arduino IDE can read your Nano. Only then you can start loading the Nano with the complicated program.
The 3d print file is HERE.
The Arduino programming file is HERE.