hoping to pick someone's brain to help me understand where i am going wrong. I have a few RGB led's (common Cathode) that i want to control via an arduino but with an external power supply. The LED's in question are these
wired up with 330R 0.5W resistors (I want to run this at 12v)
I have been using the schematic kindly put together by a different arduino forums user:
Using some of these PNP transistors I had lying around: http://www.onsemi.com/pub_link/Collateral/BC556B-D.PDF but when i wire it up the led does not fade all the way to black.. I am a bit confused as to what the fault is, my first guess is the PNP transistor, but could someone advise me what would be a more suitable one for my application?
am i also correct in my understanding that i need to have a common ground between the arduino GND and the power supply?