Big Question

How does an RGB LED display many different colors?

Investigate

You will need the following components:

Arduino UNO Board
Breadboard
1 RGB LED
5 Jumper Wires
- Medium-Length: 1 red, 1 black, 1 blue, 1 green
- Short-Length: 1 black
3 220 $LaTeX: \Omega$ Resistors

The LEDs we've used so far are each only one color. If we wanted to change colors, we would have to change out the LED. Also, we're limited by the color of LEDs that are available (5 different colors). In order to show lots of different colors we must use RGB LEDs. RGB LEDs are actually not a single LED, but 3 in one package: one red, one green and one blue. Instead of each color LED having its own cathode, the package has a single common cathode and each color has its own anode (4 wires total, see the picture below for reference). For our RGB LEDs, the cathode is the longest wire, the red and green are the next shortest and the blue is the shortest. The red anode is by itself and the green anode is between the cathode and blue anode. The case also has a flat spot (like single-color LEDs) on the side where the red anode is.

RGB LED.png

When working with light, these are the primary colors. Mixing these colors produces all the colors you are able to see in an RGB LED. In order to get lots of colors, we need to be able to mix different amounts of red, green and blue light. In the previous unit, we only turned LEDs on or off because the ports are digital. In order to use different amounts, we must be able to send analog signals to the anodes of the RGB LED. Analog signals can take on many values, typically infinitely many. Because our Arduino board is still digital, the analog values will be limited to a range of 0 to 1023 (a total of 1024 values). Furthermore, we are limited in the values we can send to the RGB LED, from 0 to 255 (256 total values).

Because the pins on the Arduino are digital, we have to use Pulse Width Modulation (PWM) to allow them to send more that just two values. The PWM pins are indicated by a tilde (~) on your Arduino board.

Procedure:

Use the medium-length black wire to connect GND to the - rail on the breadboard
Connect the RGB LED to 4 different rows on the breadboard (note where the red anode is)
Use the short-length black wire to connect the common cathode to the - rail on the breadboard
Use the 220 $LaTeX: \Omega$ resistors to connect the red, green and blue anodes to the corresponding rows on the other half of the breadboard
Use the red, green and blue wires to connect the red, green and blue anodes (plug in the same row as the resistor by itself) to three digital PWM pins on the Arduino board
Open a new sketch in the Arduino IDE
Create integers for each of the three digital pins (red, green and blue) of the RGB LED
Setup each of the digital pins as an output
In the main code, set all the digital pins to 255
Plug the USB cable into the board and computer, upload the code and observe the results
Change the values for the digital pins 3 times, each time with one color 0 and the other two at 255, reuploading the code each time and observing the results
Change the values for the digital pins 3 times, each time with one color 255 and the other two at 255, reuploading the code each time and observing the results
Change all the values for the digital pins to 0, reupload the code and observe the results

When the RGB LED has formed different colors, save the sketch as RGB_LED

Questions to answer:

What is the color of the RGB LED when all three digital pins are set to 255?
What colors appear on the RGB LED when 2 of the three digital pins are are set to 255? (Which color appears when which two pins are set to 255)
What colors appear on the RGB LED when 1 of the three digital pins is set to 255? (Which color appears when which pin is set to 255)
What is the color of the RGB LED when all three digital pins are set to 0?

Share the answers to these questions with your teacher before you move on.

Try It Yourself

You will need to add the following components:

3 Pushbuttons
6 Jumper Wires
- Medium-Length: 3 different colors
- Short-Length: 3 black

Add the following circuits:

Each button to a digital pin on the Arduino with a colored wire and to the - rail on the breadboard with a black wire

Open a new sketch in the Arduino IDE. Using the Arduino IDE reference card:

Create integers to hold the pins for the RGB LED and each of the buttons
Create bytes to hold values that will be used to set the RGB values, set each one to 0
Setup the RGB LED pins for output and the button pins for inputs pulled up to HIGH
In the main code,
1. Set each of the color pins of the RGB LED to the value stored in the corresponding byte
2. When each button is pressed, increment the value of one of the bytes by 1 (type the name, then ++; each button should change a different color)
Plug the USB cable into the board and computer, upload the code, press the buttons and observe the results

Some common problems you may encounter:

Light colors change too quickly to clearly observe
- Not enough delay between each button press
Buttons don't register changes
- Manually completing the circuit results in a change, but the button does not

Extensions

Try each of these extensions building on what you just learned and what you learned in Unit 1. Save the sketches that you create in each extension separately.

Extension 1: Random Color Generator 1.0

Challenge: Change the color of the RGB LED to a random color (random numbers for each color) when you press a button

Extension 2: Random Color Generator 2.0

Challenge: Use 3 buttons, one for each color, to randomly change the color of the RGB LED

Extension 3: Fade In and Out

Challenge: Make the RGB LED fade in and out of each color individually, each 2 color combination individually and white in a cycle

Advanced Extensions

Try these extensions after completing other lessons in this unit. Save the sketches that you create for each extension separately.

Extension 4: Potentiometer Color Control

Challenge: Use 3 potentiometers to control each of the three colors of the RGB LED

Extension 5: Photoresistor Color Control

Challenge: Use 3 photoresistors to control each of the three colors of the RGB LED

Extension 6: Joystick Color Control

Challenge: Use the joystick to control the three colors of the RGB LED