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LED strip PWM problems

Memory_Leak

Oct 27, 2015
11
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Oct 27, 2015
Messages
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I'm trying to control an RGB LED strip with PWM, but I'm having a lot of trouble. My setup is a Parallax Propeller microcontroller connected to some transistors and MOSFETS that allow it to switch 12v on and off to each color channel of the LED strip. My problem is that even with the PWM set to 60 Hz, 1% duty cycle, the lights are still quite bright. This prevents me from mixing the colors like I want to. Could it be that my LEDs have a maximum switching frequency? Or is it more likely to be a problem with transistor circuit? If anyone has any ideas I'd love to hear them.
 

BobK

Jan 5, 2010
7,682
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Jan 5, 2010
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7,682
The problem is that the response of the eye is logarithmic. It sees 1% duty cycle as probably 10% brightness. You need to use higher resolution. I have a color changing LEDs that use 256 levels, and they still have noticeable steps at times. I also have another with 4096 levels and this one changes smoothly, imperceptibly.

And, by the way, you can use 0% as well.


Bob
 

Memory_Leak

Oct 27, 2015
11
Joined
Oct 27, 2015
Messages
11
The problem is that the response of the eye is logarithmic. It sees 1% duty cycle as probably 10% brightness. You need to use higher resolution. I have a color changing LEDs that use 256 levels, and they still have noticeable steps at times. I also have another with 4096 levels and this one changes smoothly, imperceptibly.

And, by the way, you can use 0% as well.


Bob

Thanks Bob! I'll give that a try.
 

Memory_Leak

Oct 27, 2015
11
Joined
Oct 27, 2015
Messages
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I solved it! It turns out the problem was mostly my circuit and partly what you suggested. I had some unnecessary transistors switching MOSFET gates that made the MOSFETS behave oddly. Took those out and now I can mix whatever colors I want.
 
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