# Ultra Bright LED Dimmer with a sliding potentiometer

Discussion in 'LEDs and Optoelectronics' started by Dayna, Aug 14, 2016.

1. ### Dayna

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Aug 14, 2016
Hello and good day. I'm working on a simple control box for a few sets of Ultra Bright LED's. Basically on off switches and I'm adding sliding potentiometer as a dimmer. How would I go about wiring the sliding potentiometer to I guess limit the voltage? The sliding potentiometer is a B 50k Ω so it has 4 posts. Top row is numbered 3 and 1. The bottom row is numbered 2 and 2. I'm very rusty on electronics so I can use the help.

Thank you.

3
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Aug 14, 2016
3. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
The resistance is too high to use directly.

One option is to create a variable duty cycle 555 oscillator using the pot to control the duty cycle and drive the led his a resistor from the 555's output.

4. ### Dayna

3
0
Aug 14, 2016
Okay so I should pick up a few 555 Circuit?

Right now I have the power coming from a 24v power source and into a toggle switch out of that into a resistor and out to the lights.

So for the potentiometer to work as a dimmer, I would have the power going into the circuit and out of the circuit to the sliding potentiometer and from there out to the lights?

5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
24V is too high for a 555 from memory.

But if you're asking if you power the 555 circuit and it powers the LED, then yes.

Last edited: Aug 14, 2016
6. ### duke37

5,364
772
Jan 9, 2011
The potentiometer will control the on/off ratio of the 555. It will NOT have the led current going through it. The resistor in the output which has been mentioned is to limit the peak current and can be made physically big enough to dissipate the required heat.

7. ### hevans1944Hop - AC8NS

4,615
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Jun 21, 2012
The sentence I have highlighted above in red is the only thing that makes any sense so far.

To vary the intensity of your LEDs you need to vary the effective current your power source and resistor provides. The most simple and efficient way to do this is to turn the power off and on very rapidly, thousands of times per second, while being able to vary the "on" time to "off" time ratio with your slider potentiometer. To do that requires a pulse-width modulated power control with a potentiometer control input to provide a variable constant-current output to the LEDs. It would be inserted in series with your power source, toggle switch, and LEDs. The resistor would not be needed.

These devices are available all over the Internet from (usually) Asian sources. Here is one offered by Amazon for four bux American. Try looking on the UK Amazon website. If you insist on using your slider potentiometer, it will have to replace the existing potentiometer in the dimmer control box. Look on this Google page for other versions.