Electronics > Beginners
How to wire this setup?
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Youkai:
Ok guys. I think I got it working. I have the arduino and the led strip wired and they work. After a fair amount of frustration I was able to write a program that cross-fades between an array of colors. That's all good.

One minor issue though is if I use analogWrite(pin, 0) it works great for the Green and Blue LED. They both turn off completely. When I use it on the Red LED though it stays on very dim. I assume this is because there is a tiny bit of current flowing still and the reds forward voltage is less than green and blue. Is this correct? If so what do I do to fix it?

I think I need to add a resistor to bring the forward voltage on red below the threshold. Would I need to increase the resistor value for the base resistor that's already there or do I need to add an emitter resistor into the circuit?

Thanks again for all your help guys! I'm almost there :)
MarkF:
Add a diode between the transistor emitter and ground.  This will raise the threshold of the transistor base by 0.7V.  The Arduino output pin will then pull the base below the threshold and fully turn off the transistor.
james_s:
With the transistor off it shouldn't matter what the forward voltage is. Do you have a leakage path somewhere that is allowing the transistor to partially turn on?
Youkai:
A little more testing; if I pull the red transistor then the green would turn on. But if I pulled the green and red; blue would stay off. Weird. Anyway:

I turned the transistors around. The package for my transistors says the pinout for my model is different than the other ones you guys looked up. I think they are going the correct direction now. This is the orientation that was super dim in the past. This time though I have that jumper between the arduino ground and wall wart ground so they are tied. I wonder if that fixed the dimness issue. Anyway with this orientation they turn completely off; and are working at full brightness.

Seems to be fine now.
james_s:
Yeah it sounds like that's right then, if they're working then you have it connected properly. I'm not entirely sure what was going on before, maybe the protection diodes in the IO pins of the microcontroller were conducting enough current to switch on one of the other transistors.
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