Quotebut what happens to PIN 9?Nothing leave it disconnected.This pin is designed to be used with motors that generate a back EMF, by connecting this to the +ve supply will put a reverse diode across the load. You do not have to connect it to anything.
but what happens to PIN 9?
Well you still have pin 9 connected.
Do things like a PWM powered resitor exist,
Quotedo I have to connect each of the 2-8 PINs on the ULN2003 to GNDYes otherwise there is no path to ground for the current, nor common reference for the transistors.That circuit will work, providing your strip works by grounding the R, G & B signals. But it is a bit of a waste using three arrays only to use one transistor per array.
do I have to connect each of the 2-8 PINs on the ULN2003 to GND
So wich would be best to drive 5m strip (pretty much the same as op's)? Is UDN2981 what I'm looking for?