I am attempting to individual control multiple LED-based light sources via PWM. Now I am somewhat familiar with transistors and their usage, and had no issue setting up one instance of this control scheme. However when I added more transistors to the circuit, I ran into a problem. It seemed that only one PWM signal, would control all of the lights. I am new to schematics and schematic design so I could use some help figuring this out. The schematic, as I think I built it, is below.
The wiring was done with this article as reference, specifically the "light" example.
The power source is 12V 6A, which is more than enough to drive the lights I am using, which are 12V LED boards. I won't be using an Arduino in the final implementation, but I am using it currently for testing, so assume that is where the PWM is coming from. Oh, and the transistors are TIP31 NPN units.
As I said previously, the issue is that when using the circuit, the lights will only respond to one PWM signal and they will both use that value seemingly. Otherwise it works just fine. My only thought is that it could be an issue with them sharing a common ground? But if so, what is the best way to isolate them?