Deva_Rishi:
The Capacitor isn't really needed, since there should be a big enough one in the stepdown 15v-5v if it's a good one.
So, you either failed to read, or simply did not understand my previous post then?
MrDankYT:
OK i redrew it is this fine now?
Let's see:
Well, a very poor diagram which does not covey a sense of order in the project.
I personally do not care a fig about which way up the diodes are in the box. Since they are not diodes anyway but actual ASIC ICs, better to simply have three wires stuck out the side of the box which do not pretend to attach to the diode wires.
A diagram which confuses the direction of signal and/ or power flow makes it difficult to follow, and somewhat worse is one which muddles the polarities. Almost always now, ground is the negative supply and your supply feed is the positive. It is expected that ground is at the bottom and VCC - positive is at the top. Swapping them over in the step down converter is a source of confusion and having the ground wire make a "home run" to connect is not only confusing, but visually works against my admonition to keep all the wires closely together.
And given that you have a 5 V regulated supply, it makes no sense whatsoever to supply the Nano with a power bank; just wire it from the LED strip as I explain in every previous post here.