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Materials needed: 

-10k potentiometer (variable resistor)
-Breadboard
-LED
-9V battery
-9V battery connector
-Wire
-1k resistor
-250 - 270 ohm resistor

Note: You can get all of these objects at RadioShack

Step 1: Putting Potentiometer in Place

-Take the red and black wire from the battery connector and put them on the side rails.
-Attach a wire to each lead from the potentiometer and place on breadboard
-Put the LED somewhere on the breadboard

Step 2: Putting Resistors in Place

-Put 1k resistor in the middle lead of the potentiometer and put the other end in a different rail
-Put the 270 ohm resistor in the longer lead of the LED and attach to same rail as 1k

Step 3: Wiring

-Attach the left end of the potentiometer to the positive of the battery
-Attach the right end of the potentiometer to the negative (ground) of the battery
-Attach the shorter lead of the LED to the negative on the battery

Step 4: Finished Product

     Connect the battery and turn the potentiometer and the brightness of the LED should change. If it doesn't make sure you did everything correctly.
     What this circuit basically does is that it increases and decreases the voltage the LED gets by changing the resistance. You can change the value of the resistors to make the LED brighter or dimmer.
<p>LED is operating on current not on Voltage. Every LED have their own threshold current. Can we consider while selecting potentiometer resistance?</p>
<p>Yes that is something to consider while using this technique. For example, if you use a 9 volt battery, as I did in this instructable, and decide to use a 500 ohm potentiometer instead, the LED will most likely experience minimal change in brightness because there would still be quite a bit of current still reaching it regardless. A 10k ohm potentiometer was the only one I had available at the moment of writing this instructable and, for me, is my go to potentiometer value.</p>
<p>Some people might say &quot; You can't controll led brightness by changing voltage&quot;. But i did it , just like you did it (same schematics), fortunately- before reading those people opinion. The bee fly, for- no one told the bee it can't. :) </p>

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Bio: Computer science major at Marquette University, Milwaukee.
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