How to Use an RGB LED

How to Use an RGB LED

An RGB LED is actually three LEDs in one bulb. The housing contains separate red, blue and green LEDs which share a common cathode, or negative terminal. The brightness of each color is determined by its input voltage. By combining the three colors in different amounts, you can turn the LED any color you want. This circuit demonstrates the use of an RGB LED by using a potentiometer to control the voltage going to each color. A potentiometer is a variable resistor controlled by a knob, like the volume dial on your stereo.


Instructions
1
Connect the battery clip to the power and ground rails of the breadboard. The red wire from the battery clip connects to the power supply rail, and the black wire connects to ground. Do not put the batteries in the clip yet.

2
Place the LED on the breadboard so that the four pins are not connected to each other. Connect the longest pin, the cathode, to ground. Consult your LED's datasheet to confirm which pin is which, as it may vary with different manufacturers.




Calculate the resistor value you will need for each pin. Different color LEDs have different maximum voltage ratings, so consult your LED's datasheet, which will list the maximum forward voltage for each color. Calculate resistor values using Ohm's law, which states that resistance equals voltage divided by current, or R = V/I. For each color, subtract the maximum forward voltage from the supply voltage. The result is the voltage you need to drop across the resistor. Plug in the resistor voltage for V, and divide by .02 for current. The result is the minimum resistor value you should use for that color.

4
Connect the first resistor to the positive power rail, and then to the left terminal of a potentiometer. Connect the center terminal of the potentiometer to the appropriate leg of the LED for this color. Connect the right terminal of the potentiometer to ground. Repeat for the other two colors. The potentiometer will act as a voltage divider, so the actual resistance value of the potentiometer is irrelevant. Turning the knob on the potentiometer will set the voltage to any position between 0 volts and the maximum forward voltage, controlling the brightness of the color.

5
Connect the batteries to the clip, and the LED will light up. Control the color by turning the three potentiometer knobs. Each knob controls the brightness of its own color.



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