Dear,I'm rather busy right now.If you still want to go the way of using shift registers, I strongly suggest having a look at the Arduino "ShiftPWM" library! It takes away all of the hard work for you.https://github.com/elcojacobs/ShiftPWMBest,Robert
Latest code:https://github.com/madworm/V3_x_boards_test?files=1In the first few lines you'll find the pin numbers. "Digital" pins 9 - 13 on the UNO and compatible ones. Same numbers on the other board. They should be printed on the PCB.
Better look at "shiftPWM" or use adafruit neopixel / WS2812B.
I haven't looked at the differences closely. Most likely difference in timer interrupts (naming & which one is free to use) / register naming.
Possible yes, advisable no.You'd be better off with one much more powerful microcontroller, than having to deal with syncing up many very busy one.I'd look into WS2812B LEDs or similar, so driving the LEDs themselves is much simpler & doesn't occupy most of the cpu time.
JOIN OUR OPEN SOURCE ELEMENT DRESS!
Beautiful acetone lamp from reused materials.