12v RGB LED Strip????

does anybody know?... I am trying to use an Arduino to control an RGB LED strip that has a common cathode and an anode for each color. I am using a TIP 120 and 2.2K resistors to get my current and voltage right, just can't seem to figure out how to get 3 PWM Arduino pins working for the colors. Any advice?

If you have a common cathode display then you should probably use a PNP transistor (or P-type MOSFET) to drive each color rather than a TIP120.

Here's an example for driving a 12V solenoid -- you can use the same circuit and eliminate the diode D1 since the RGB LED's are not an inductive load.


The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

thank you sooo much!!! I'll see whats up and post again after I try it.

ok... from the circuit I see that I can use a P2N2222A for T1. But I might not have a TIP 137 for T2. Is there any substitutes that will work?

Any general-purpose PNP transistor that can handle your RGB LED strip current (what is it?) should work.

Some other common part numbers that might work are 2N4402, 2N4403, BC327, PN2907, MPSA55, MPSA56. But really, there are a LOT of PNP transistors out there.

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My LED strip is an OLS light strip. They are 12v and 2amp. Common cathode and three anodes for the colors. I am trying the circuit mentioned above with not much luck. Any ideas?


also... I am connecting two of them end to end. Not sure if that's going to double the amps or not.

Can you sketch out how you have things hooked up? "End to end" doesn't really make sense.

Also, for 2A the transistors I suggested aren't going to be able to handle the current. Something like a 2SB1274S would be more appropriate, but really at 2A I'd use a P-channel MOSFET. Like this circuit, which should work just as well at 12V instead of 6V:


Beat707: MIDI drum machine / sequencer / groove-box for Arduino

each strand of LED lights has four holes on each end for a four prong runner/runner cables. So with runners I have connected two strands together end to end. There is one pin for the cathode, and three anodes for the RED, GREEN, and BLUE lights. Below is a link to the amazon description. I believe that each strand rates at 12v 2amps. That's what I read from the manufacturer. I do not have any special power supplies or adaptors. Just the LED strands, an Arduino, and a 12v power supply. I have one mosfet transistor, but I will need to get ahold of some more to complete the project.

I have an Arduino being controlled by MIDI from Ableton Live and Max 4 Live. SO far I have controlled some simple RGB LED's with my keyboard and drum beats. Now I want to use this bigger LED strand to mix the colors as various filters process my music. THANKS FOR YOUR HELP!!!!


@Moloko, Interesting that those strips are common cathode. Many are common anode, like the ones shown here: http://arduino-info.wikispaces.com/Brick-4ChannelPowerFetSwitch

I am thinking of building some similar FET switch modules that are high-side switches that would work for applications like this..

Anyone have comments or suggestions on this idea??