How do I use a pot to dim an LED strip? Answered


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I have hooked up a 5k pot to this thing, and it dims it ok but
1) how do I get a fuller range of dimming? it only dims towards the last 45 degrees. Any higher value (10k, +) gives worse results. Do I need 1k pot? Is there a way to make the 5k work better?
2) even when the pot is all the down, the led is still dimly lit. Please make it go away.
3) Do I need to use all three terminals on the pot?

As you can tell from my questions, I am slightly above doofus level so please be kind.



Typically you don't use only a pot to control LED brightness. You take an extra thirty minutes and build a 0 - 100% variable duty cycle oscillator from a 555 with a power mosfet to handle the current load. That gives you the best results, if you have the parts, time, and inclination, etc.. But I realize that is not the question you asked. :) Here's the answer. Set pot at the lowest useful setting, e.g. 45 degrees before bottom of range or whatever that setting is. Then take the pot out of circuit, and measure the resistance with an ohm meter. Then you buy a pot that is close to that value. So if you read, for example, say your read 830 ohms at that setting. Go buy a 1K pot, since that is the closest commercial value generally available. You can use your best judgment to pick what standard value pot will work best for the resistance you get from your test. And you should be OK with 1/4 watt pot.

Hey thanks for the idea, but now I'm really interested in this mysterious variable duty cycle oscillator. I would make one if I only knew how.....Can you point me in the right direction?

No mystery. The 555 has been around for thirty years that I personally know of. People have written whole books about it, they've had their run, and they've gone out of print. Mature technology. Good chip with which to get familiar. Here's a link to get you started. Cheers!

You don't need all three terminals on the pot. What I would recommend is a resistor and the pot you have. It sounds like your biggest problem is that you can't get a full range of dimming (bright to off). I don't know exactly what value of resistor you'd need though. I'm really bad at resistor math.