Now it’s time to solder the three squares (of nine LEDs each) to each other. I like using a pair of helping hands to hold each row above the previous while soldering the positive, straight legs of the LEDs to each other.
The bottom square of LEDs’ positive legs should be soldered into the holes in the PCB, as noted in the second photo of this step.
The three stripped wires that connect each row go to their respective holes on the PCB – “Plane 1” for the bottom, 2 for the middle, and 3 for the top. It doesn’t matter what part of the square you solder the wire to – just make sure it’s connected to the horizontal, or negative, legs of the LEDs.
And that’s it! Plug it into your Arduino and download some code here.