PWM + 5V USB RGB Led Strip

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didanix
 
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PWM + 5V USB RGB Led Strip

Post by didanix »

I just got a USB powered 5V RGB Led Strip from eBay (http://www.ebay.co.uk/itm/5050RGB-led-s ... OC:GB:3160) and while it does have a built-in controller, I'd like to interface it with an Arduino's PWM pin(s).

After testing a basic PWM circuit, I noticed that when I try to set the LED brightness via PWM, the brightest setting (0?) is still pretty dim. If I connect it directly to GND (and not PWM), I get the full brightness, but then I have no control over it.

The strip has the following pins:
+ - Power (connected to Arduino's +5V)
G - Green (connected to Arduino's PWM pin)
R - Red (connected to Arduino's PWM pin)
B - Blue (connected to Arduino's PWM pin)

I'm just a hobbyist, so I'm probably missing something, but this is also the first time that I've had to dealt with a circuit with no actual GND pin anywhere. I also couldn't find anyone else with this type of LED strip that works just fine with 5V and over USB, so no external power source required.

Ideally, I'd like to manually be able to change the brightness and RGB colors through the Arduino, but I'm a bit lost on how to build the circuit. Anyone care to comment?

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adafruit_support_bill
 
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Re: PWM + 5V USB RGB Led Strip

Post by adafruit_support_bill »

You can't drive these directly with an Arduino pin. The current levels required by the strip will damage the pin. The strips are designed for low-side switching, You need something like a MOSFET between each R, G, B pin and ground. The gate of the MOSFET is switched by the Arduino PWM pin. http://learn.adafruit.com/rgb-led-strips/usage

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didanix
 
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Re: PWM + 5V USB RGB Led Strip

Post by didanix »

I see, I didn't think I'd still need MOSFETs like with the 12V strips, but I guess that would make sense. Just didn't even think about it since it works using regular USB power.

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