Lesson 5 – Pulse Width Modulation


  1. Before you start working with any of the tutorials in this series please make sure you have completed the following tasks –
    1. Downloaded and installed the Arduino IDE.
    2. Are able to connect to the Arduino IDE from your computer
    3. Have been successful in uploading a simple (e.g. Blink LED’s) example programs (that comes with the Arduino IDE) onto your Arduino UNO board
  2. If you haven’t installed the Arduino IDE please head back to the first tutorial and make sure you’ve gone through each of the steps involved.
  3. Once you’ve sorted all of the above you are ready to move onto the next tutorial.


PWM, short for Pulse Width Modulation, is a technique used to encode analog signal level into digital ones. A computer cannot output analog voltage but only digital voltage values such as 0V or 5V. So we use a high resolution counter to encode a specific analog signal level by modulating the duty cycle of PMW. The PWM signal is also digitalized because in any given moment, fully on DC power supply is either 5V (ON), or 0V (OFF). The voltage or current is fed to the analog load (the device that uses the power) by repeated pulse sequence being ON or OFF. Being on, the current is fed to the load; being off, it’s not. With adequate bandwidth, any analog value can be encoded using PWM. The output voltage value is calculated via the on and off time.

Output voltage = (turn on time/pulse time) * maximum voltage value

PWM has many applications:  lamp brightness regulating, motor speed regulating, sound making, etc.  The following are the three basic parameters of PMW:

  1. The amplitude of pulse width (minimum / maximum)
  2. The pulse period (The reciprocal of pulse frequency in 1 second)
  3. The voltage level(such as:0V-5V)

There are 6 PMW interfaces on Arduino, namely digital pin 3, 5, 6, 9, 10, and 11. In previous experiments, we have done “button-controlled LED”, using digital signal to control digital pin. This time, we will use a potentiometer to control the brightness of LED.

Here’s the hardware you will need for the tutorials –

  1. Potentiometer*1
  2. Red M5 LED*1
  3. 220Ω resistor
  4. Breadboard*1
  5. Breadboard jumper wire *6

The input of potentiometer is analog, so we connect it to analog port, and LED to PWM port. Different PWM signal can regulate the brightness of the LED.

You will find fritzing diagrams below outlining circuit connections for both the Arduino Uno and the Arduino Mega 2560.

In the program compiling process, we will use the analogWrite (PWM interface, analog value) function.  In this experiment, we will read the analog value of the potentiometer and assign the value to PWM port, so there will be corresponding change to the brightness of the LED. One final part will display the analog value on the screen. You can consider this as the “analog value reading” project adding the PWM analog value assigning part.  Below is a sample program for your reference.

int potpin=0;// initialize analog pin 0
int ledpin=11;//initialize digital pin 11(PWM output)
int val=0;// Temporarily store variables' value from the sensor
void setup()
pinMode(ledpin,OUTPUT);// define digital pin 11 as “output”
Serial.begin(9600);// set baud rate at 9600
// attention: for analog ports, they are automatically set up as “input”
void loop()
val=analogRead(potpin);// read the analog value from the sensor and assign it to val
Serial.println(val);// display value of val
analogWrite(ledpin,val/4);// turn on LED and set up brightness(maximum output of PWM is 255)
delay(10);// wait for 0.01 second

After uploading the program, when you rotate the potentiometer knob, you can see the value change, and also obvious change of the LED brightness.


This development track requires an investment a bit of hardware. See below for details –

  1. Arduino IDE –
    1. You will need to download and install the Arduino development IDE.
    2. The approach to installation, configuration, setup of the Arduino IDE is covered in our tutorials.
  2. Arduino Uno, Sensors, etc. –
    1. You will need to purchase the Super Learning Kit for Arduino from OzToyLib.
    2. The Arduino Advent kit has all the sensors you need to perform the tutorials covered in this development track.
    3. If you do not have an Arduino Uno or Arduino Mega 2560 you might want to head over to Arduino boards and pick one up now.

The Super Learning Kit for the Arduino kit has all the sensors you need to perform the tutorials covered in this development track.

About the Super Learning Kit for Arduino

The Super Learning Starter Kit for Arduino comes packed with ~35+ different electronic bits (Sensors, LEDs, switches, LCD, servo, etc.) and can be purchased with either the Keyestudio UNO R3 or the Keyestudio Mega 2560 board. The Keyestudio Arduino boards can be used to interface with the different electronic bits i.e. sensors, LED’s, switches, servos, etc. included in the starter kit. The starter kit for the Keyestudio Uno R3 offers a great opportunity to explore the world of electronics using the Arduino Development Platform. Interact with the real world through the various sensors, create innovative projects, learn how to program the micro:bit to read data from the sensors and perform certain actions. The starter kit for the Arduino is a great way to dive into the awesome world of electronics and get started with your own STEM (Science, Technology, Engineering, Math) learning journey.

The Arduino advanced study kit walks you through the basics of using the Arduino in a hands-on way. You’ll learn the fundamentals of electronics and working on the Arduino through building several creative projects. The kit includes a selection of the most common and useful electronic components with a book of 32 projects. Starting the basics of electronics, to more complex projects, the kit will get you interacting with the physical world using sensor and actuators. Along with the kit you get access to detailed tutorials and wiring diagrams.

You can purchase the Super Learning Kit for Arduino from OzToyLib.

About the Arduino UNO

The Arduino UNO is the most used and documented board of the whole Arduino family and very easy to setup, play with. The Arduino UNO is a microcontroller board based on the ATmega328 . The Arduino UNO has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. Here’s a listing of the some of the features of the Arduino UNO –

  1. Microcontroller: ATmega328
  2. Operating Voltage: 5V
  3. Input Voltage (recommended): 7-12V
  4. Input Voltage (limits): 6-20V
  5. Digital I/O Pins: 14 (of which 6 provide PWM output)
  6. Analog Input Pins: 6
  7. DC Current per I/O Pin: 40 mA
  8. DC Current for 3.3V Pin: 50 mA
  9. Flash Memory: 32 KB of which 0.5 KB used by bootloader
  10. SRAM: 2 KB (ATmega328)
  11. EEPROM: 1 KB (ATmega328)
  12. Clock Speed: 16 MHz

Arduino is an open-source, prototyping platform and its simplicity makes it ideal for hobbyists to use as well as professionals. The Arduino UNO contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Arduino UNO differs from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega8U2 microcontroller chip programmed as a USB-to-serial converter. “Uno” means one in Italian and is named to mark the upcoming release of Arduino 1.0. The Arduino Uno and version 1.0 will be the reference versions of Arduno, moving forward. The Uno is the latest in a series of USB Arduino boards, and the reference model for the Arduino platform.

You can read more about the Arduino here – www.arduino.cc.