Project 4

RGB LED Dimmer

Overview

You will program an Arduino Nano to control a dimmable RGB light. At each checkpoint, you will explore the core functions of microcontrollers: digital input/output, pulse width modulation, and analog-to-digital conversion.

Concepts

Arduino Nano

The Arduino Nano is a board based on an ATmega microcontroller. The chip itself contains the processor, RAM, and flash storage. These components execute the programs we write.

The Arduino company designed several boards to make the ATmega chip hobbyist-friendly: they added a USB port, voltage regulator, and onboard LEDs (among other things). In this family of boards are the Arduino Uno, Arduino Nano, and many, many more.

We'll stick with the Arduino Nano for now, which is depicted here.

General Purpose Input/Output (GPIO), power, and reset pins run along the sides of the Nano.

In the lecture content, we discuss the different GPIO pin capabilities and their use cases. We also use the Arduino programming language (a C++ variant) to write and compile sketches. Learn more here.

We won't talk in depth about each function or data structure from the Arduino Library. When you need to read up on Arduino code, refer to the Arduino Language Reference.

Pinout

Thinking about using a pin but you don't know what it does? Refer to the Arduino Nano pinout diagram. The full datasheet is linked in the Parts section.

~ represents pins that are PWM capable.

Potentiometer

A potentiometer is a is a three-terminal variable resistor. We will use it as a voltage divider, a circuit which accepts a supply voltage and outputs a voltage which is a fraction of the supply voltage. The voltage of the potentiometer's output pin ranges between the VCC and GND pin voltages, depending on the dial's position.

How it Works

We just referred to the potentiometer as a kind of resistor. Why? Internally, a resistive strip connects its VCC and GND pins, and a rotating wiper connects the output pin to the strip. The greater the distance along the strip between the wiper and the VCC pin, the greater the resistance between the wiper and VCC.

In this voltage divider configuration, the wiper reduces the voltage at the output pin the further it is turned clockwise (toward GND).

Using it with Arduino

We can connect the potentiometer's output pin to one of the Nano's analog pins (see its pinout above). The analog pin is wired to the analog-to-digital converter (ADC) inside the Nano's ATmega chip. The ADC is hardware that translates the analog signal to a discrete digital signal. Using analogRead(), we interpret the pin's analog voltage as a discrete integer in the range 0-1023.

RGB LED

For this project, we will use a common cathode RGB LED. Inside this component are three smaller LEDs - one red, one green, and one blue. They are all connected by a shared or common cathode.

This RGB LED has four pins: One is the common cathode, and the other three are the red, green, and blue LED anodes.

Using it with Arduino



In the world of digital electronics, color is often represented in the 8-bit RGB color model. Every visible color is identified by an encoding of the three base colors: red, green, and blue. In our Arduino code, we will set the intensity of each base color to a value in the range 0-255.

Try the RGB Color Picker. Adjust the slider at the bottom of the application. Notice how the three values in the RGB field change as you select different colors.

Recall that LEDs are current driven: we control the intensity of each RGB LED color by increasing/decreasing the current passing through its pin. With the Arduino board, we set the voltage, which changes current flow (recall Ohm's Law).

Here's the rub: digitalWrite() can only set a pin's voltage to 0 or 5V (the supply voltage). If we want to dim an LED, we need a new function that can output voltages between 0 and 5.

We will use a pulse width modulation or PWM signal - a digital waveform mimicking analog voltage signals. With PWM waves, we can generate analog voltages like 2.3V or 4.1V. In Arduino, we accomplish this using analogWrite().

Only certain Nano pins are capable of PWM, as indicated in the pinout above.

Software Installations

We will use the Arduino IDE to write code for our Arduino Nano board. The software includes a text editor, compiler, debugger, and library manager. While you may use any IDE of your choice, we highly recommend installing Arduino IDE, so you can follow our lectures and projects with ease.

Arduino IDE

Visit this link to download the installer for Arduino IDE 2.0.0+ . Make sure to select the installer appropriate for your system.

Open the installer and follow its instructions. Easy peasy!

If you want to know more about using the Arduino IDE, check out our lecture content here.

CH340 Driver

There is an IC known as the CH340 on the Arduino Nano board responsible for converting USB signals to a signal the Nano's ATmega chip can understand. This ultimately allows us to connect our computer to the Nano over USB.

For your computer to connect with the Nano, we need to install a software driver that tells the computer how to communicate with the CH340.

Visit this link to download the installer for the CH340 driver. You may have to scroll down the page a little. Make sure to select the installer appropriate for your system.

Requirements

LED Blinker

  • You must build a blinking LED circuit.
  • The LED in the circuit must blink once per second.
  • The LED must be brightly lit when turned ON.
  • The LED must be completely dark when turned OFF.
  • The circuit must be built on a breadboard.

LED Dimmer

  • You must build a circuit with a dimmable LED.
  • The user must be able to adjust the LED's brightness from 0% to 100% when turning the potentiometer dial.
  • When turning the potentiometer clockwise, the LED should brighten.
  • When turning the potentiometer counter-clockwise, the LED should dim.
  • The circuit must be built on a breadboard.

RGB LED Dimmer

  • You must build a circuit with a dimmable RGB LED.
  • The user must be able to adjust the RGB LED to any color when turning the three potentiometer dials.
  • Each potentiometer should control the light intensity of one of the three LED colors (red, green, and blue).
  • When turning a potentiometer clockwise, its respective LED color should brighten.
  • When turning a potentiometer counter-clockwise, its respective LED color should dim.
  • The circuit must be built on a breadboard.

Parts

Part Name Qty
Jumper Wire X?
Breadboard 1
Potentiometer, 10kΩ 1
LED, 3.2V 1
LED, RGB, Common Cathode 1
Arduino Nano 1
Resistor, 130Ω 1
Resistor, 430Ω 2
Resistor, 470Ω 1
Nano-compatible USB Cable 1

Schematics

Instructions

Checkpoint 1

  1. Build the circuit from Schematic A (LED Blinker) on your breadboard. You will design a blinking LED using the Arduino Nano. 
    // Assign variable to pin number for LED

void setup() {
	// Configure LED pin's behavior to OUTPUT
	// Configure the Serial baud rate
}
						
void loop() {
	// Set LED pin to HIGH
	// Delay
	// Set LED pin to LOW
	// Delay
}
  2. Upload your sketch to the Arduino Nano, and verify that the program executes as expected; the LED should cycle ON and OFF.

Checkpoint 2

  1. Build the circuit from Schematic B (LED Dimmer) on your breadboard. Your goal is to make the LED grow brighter as you twist the potentiometer clockwise. 
    // Assign variable to pin number for LED
// Assign variable to pin number for Potentiometer

void setup() {
	// Configure the LED pin's behavior to OUTPUT
	// Configure the Potentiometer's pin behavior to INPUT
	// Configure the Serial baud rate
}
						
void loop() {
	// Read potentiometer pin value
	// Set LED pin to the potentiometer pin value					
}
  2. Upload your sketch to the Arduino Nano, and verify that the circuit meets the design requirements.

Checkpoint 3

  1. Build the circuit from Schematic C (RGB LED Dimmer) on your breadboard. No pseudo code this time! You are on your own.
  2. Upload your sketch to the Arduino Nano, and verify that the circuit meets the design requirements.

Deliverables (Enrolled Students Only)

Students enrolled in the course must submit the following deliverables to the corresponding Canvas course assignment.

Place the following files in a single folder:

  • Video of the RGB LED Dimmer (Schematic C) on a breadboard Compress the folder to a zip file and rename the file using the format “ops_project#_lastname_firstname.zip” Then, submit the zip file to the Project 4 Canvas assignment.