User manual

LPCXpresso Experiment Kit - User’s Guide

Page 61

7.8 Control an RGB-LED

In this experiment you will learn how to control an RGB-LED. Inside the package of the component

there are three LEDs, one red, one green and one blue. The common anode is connected to the +3.3V

supply and series resistors for each LED will limits the current to suitable levels (not irritating) with

matching lamination from each LED. Note that the series resistor for the red LED is 1.5 kohm and 220

ohm for the blue and green LEDs. Also note that the current levels are quite low compared to what a

normal RGB-LED would have.

Figure 29 – RGB-LED, LED10, on Schematic Page 4

The anode is connected to +3.3V as shown in Figure 29. The pcb has shorted jumper SJ1, while SJ2

is open. There is an option to connect it to +5V instead but the currently used RGB-LED works well

with +3.3V supply. Normally the problem is the blue LED, which has high forward voltage drop.

Typically in the region of 3.5-4.5V. The used RGB-LED has V

= (about) 3.2V. That is also a reason

why the current levels are quite low.

The RGB-LED component is also shown in Figure 29. From left to right the four pins in the picture are:

 Red-LED cathode (connected to R26)

 All LEDs anode (connected to +3.3V via SJ1, which is closed)

 Green-LED cathode (connected to R27)

 Blue-LED cathode (connected to R28)

7.8.1 Lab 7a: Test RGB-LED

In this first experiment with an RGB-LED the microcontroller will not be used. We will only use the

LPCXpresso board to get the +3.3V supply. With three LEDs there are eight combinations. Verify that

you can create all seven colors (besides black/dark). Insert the resistors in seven different

combinations as shown in Figure 30 below.

Which colors do you get? ____________________________________________________________