LEDs and Power

I just got 2 sets of RGB LED lightstrips from DealExtreme. Using just the onboard 5V power supply of the Arduino, the lights were very dim, but I expected this because the site recommended 12V AC. So I rummaged around my house and found a 9V AC wall wart, plugged it into the Arduino, and the lights worked nice and bright. But after experimenting around with them, it seems that no matter what I do I cannot turn the red LED all the way off. Turning the pin high (the lights are common cathode) just dims it down to about 10 percent its maximum brightness. If anyone could help I would appreciate it.

Please describe or draw the actual circuit you are using to control the LED strips. If you are just connecting them to the Arduino at 12V you are about to destroy something. Are you sure they're common cathode instead of common anode? And if you set the Arduino output to HIGH, it would be 5V, and therefore would still be 7V across the LEDs. For red, this is enough to light them...green and blue would need at least 9V. That would explain why red won't turn off, though it still means you're avoiding the destruction of your Arduino by some unknown miracle.

Additionally...you probably do not want to be using AC.

Sorry, meant to be DC, not AC. And what I currently have is the common cathode in the Vin pin and the red, green, and blue pins going to 9, 10, and 11. And then the wall wart plugged in obviously.

OK, so you definitely have common ANODE, not cathode. Common cathode would be if you had the common pin connected to GROUND.

Please disconnect everything right now and don't use it anymore. You are putting 12V on the Arduino pins, and they are not rated beyond 5.5V, so you will probably destroy the Arduino very soon. You will need to drive the RGB strip using transistors.

http://www.dealextreme.com/p/rgb-multicolored-1-meter-30-led-6w-light-strip-dc-12v-14965

Is this similar? If so, AC probably won’t damage the LEDs but its not reccomended as you need to keep the arduino safe. Also, you will NEED to get an alternative way of triggering the light strip, Arduinos dont handle high loads well.

If you grab one of these, you can take the top PCB off it and use the control circuits on it to do a huge amount of functionality, this solves both the power and the control issues.

Yes that is the exact product I purchased, but I'm already going to be using a TLC5940 because I'm going to split the strips into 3 light sections. And I've been playing with the lights for the past half hour and it doesn't seem as if anything is melting or smoking, but if you think it will damage the board I'll unhook them. So, what would you suggest to be my next step? The final project I'll be making is a light bar with 10 different sections that can be individually controlled. So, I plan to split up the 2 light strips into sections of 6 and have the 30 pins of the RGBs be controlled by two TLC5940s.

You may what to do something like this http://fritzing.org/projects/arduino-knight-rider-with-8-blue-12v-led-modules/ but instead of single color LED Modules use the RGB strips

if you want to control a lot of them up to 32 RGB lights then you may want to use 595 style shift registers http://code.google.com/p/fastspi/

So, I bought a set of 2N2222 transistors, and I have it setup what I think is correctly. But, do I need any type of resistor going from the Arduino pin to the base of the transistor? I don't see why I should need it but I'm not too sure. Thanks.

cereeal: So, I bought a set of 2N2222 transistors, and I have it setup what I think is correctly. But, do I need any type of resistor going from the Arduino pin to the base of the transistor? I don't see why I should need it but I'm not too sure. Thanks.

Yes there is always a series wired resistor needed between a digital output pin and the base of a NPN transistor with the emitter connected to ground. This sets the base current which times the current gain for the specific transistor determines how much collector/emitter current can flow.

Lefty