PAGE 086 OF 150 · TIMERS, FLASHERS & DIMMING
Potentiometer Dimmer Circuit
A variable resistor adjusts brightness by hand.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Basic idea
A potentiometer is a variable resistor. Placed in series with an LED it changes the current and so the brightness.
Protect the LED
Always add a fixed resistor so that the minimum total resistance still gives a safe current. For 5 V and a red LED at 20 mA, use at least 150 ohms fixed, then add a 1 kilohm pot. The current then ranges from about 20 mA down to about 2.6 mA.
Better dimmer
Use the pot as a voltage divider that drives a transistor, so the pot only carries tiny currents and the transistor handles the LED.
REMEMBER
Switching an LED on and off quickly can look like steady dimmer light.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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