So I am driving 16 strips of LEDs using 2 595 shift registers. (right now only 4 strips are connected for testing) The strips require 18V so I am using transistors rated at 50V 500mA max. I have the 18V+ connected to the collector, Q0 (LED pin on the 595) to the base and 18V- to the other side of the LEDs.
Now I have heard that you have to 'link' the power supplies (5V Arduino and 18V primary) so I attached the 18V- to the GND on the Arduino. Doesn't work. :(
Interestingly though when I connect a single LED to the emitter of one of the transistors (with appropriate resistor of course) and connect it to Arduino GND, and at the same time break off the connection between 18V- and GND, the remaining 3 LED strips mimic the single LED (on 595pin 3). So if I send the 595 '00000100' all the strips light up. I am very confused and feel I don't understand how to properly use 2 power supplies and a switching transistor together. Any help would be great. (I hope I move one wire and everything is great!) :)