Difference between revisions of "Arduino/C2/Pulse-Width-Modulation/English"

Learning Objectives

• PWM i.e Pulse Width modulation
• PWM Duty Cycle
• PWM Frequency
• L293D Motor Driver IC

Pre-requisites

• Electronics and
• C or C++ programming language

System Requirements

• Arduino Uno board
• Ubuntu Linux 16.04 OS
• Arduino IDE

External Components Required

• Breadboard
• 10K Ohm Potentiometer
• LED
• 220 ohm Resistor
• Jumper Wires
• Push Button

Image DC-motor.jpg

Image L293D.jpg

Pulse Width Modulation

• PWM signal is a square wave signal which has a high frequency i.e (1KHz).
• PWM is a technique by which the width of the pulse is varied.
• It is done while keeping the frequency of wave constant.

Pulse Width Modulation

• PWM signal consists of two main properties that define its behaviour.
• They are Duty Cycle and Frequency.

Image duty_cycle.jpg

Duty cycle can be varied from 0% to 100%..

Formula - Duty cycle

Image duty_cycle_formula.jpg

• tON is equal to the duration of time when signal is high.
• tOFF is equal to the duration of time when signal is low.
• Time Period is tON + tOFF.
• i.e. It is equal to the sum of on time and off time of PWM signal.

PWM frequency

• Frequency determines how fast the PWM completes a cycle.
• i.e. How fast it switches from HIGH to LOW states.

Example - Duty Cycle

This will control the brightness of LED.

Image Arduino_PWM_pins.png

Pins 3, 5, 6, 9, 10, 11 on Arduino Uno are PWM channels.

PWM channels are denoted by tilde sign.

Image LED_Connection.png

Connect cathode leg of the LED to ground.

LED_connection_setup.png

Do the connection as shown in the image.

We will write a program to change the brightness of LED using PWM pin.

int duty_cycle_value = 1;

We have assigned the PWM pin 9 to the variable LED_Pin.

We have initialized duty_cycle_value as 1 for an LED to turn ON.

{

pinMode( LED_Pin, OUTPUT);

}

We have declared pin 9 of the Arduino as OUTPUT.

Let me explain the code.

While loop executes the code till the duty_cycle_value is below 255.

analogWrite() function is used to generate PWM signal.

We are passing two parameters. i.e PWM pin number and the duty cycle value.

The duty cycle value must be between 0 to 255 i.e between (0v) and (5V)

We will keep a delay of 3000 millisecond i.e. 3 seconds

A pop up window will appear to save the current program.

Let us save the program as LED_Brightness and click on the Save button.

Now click on upload button to upload the current program on Arduino.

LED_output.mp4

Image L293D_Pinout.png

The speed of the motor is controlled by EN 1 and EN 2 of the IC.

The direction of the motor is controlled by IN1, IN2, IN3, IN4 of the IC.

We can control 2 motors at a time using this IC.

In our experiment, we will connect only one DC motor.

Image Speed-Direction-Control-Connection.png

• Pin 1, pin 8 and pin 16 of driver IC are connected to 5V.
• Pin 4 and pin 5 of driver IC are connected to ground.
• Pin 2 and pin 7 of driver IC are connected to pin 11 and pin 10 of Arduino.
• 2 push buttons are connected to pin 12 and pin 13 of Arduino.
• These push buttons are used to control the direction of DC motor.
• 10Kohm potentiometer is connected to control the speed of the DC motor.
• Middle pin of potentiometer is connected to analog pin A0.
• Pin 3 and pin 6 of driver IC are connected to DC motor.

Do the connection as shown in the image.

Image Live Setup

I have fixed a wheel on the shaft of the motor.

This will help to see the rotation and varying speed of motor clearly.

Now we will write a program for this circuit to work.

const int potPin = A0;

const int fwdbuttonPin = 13;

const int bckbuttonPin = 12;

const int ICpin2 = 11;

const int ICpin7 = 10;

We have initialized the connection between Arduino and driver IC.

Potentiometer pin is connected to analog pin A0.

fwdbuttonPin is the variable for push button connected to pin 13 of Arduino.

bckbuttonPin is the variable for push button connected to pin 12 of Arduino.

ICpin2 and ICpin7 are the variables which indicate pin 2 and pin 7 of IC.

They are connected to pin 11 and pin 10 of Arduino respectively.

int motorValue = 0;

int fwdbuttonState = 0;

int bckbuttonState = 0;

For that we have initialised it to 0.

{

pinMode(fwdbuttonPin, INPUT_PULLUP);

pinMode(bckbuttonPin,INPUT_PULLUP);

pinMode(ICpin2, OUTPUT);

pinMode(ICpin7, OUTPUT);

}

pinMode function defines the pins as INPUT or OUTPUT.

fwdbuttonPin and bckbuttonPin are set to INPUT_PULLUP mode.

In this mode we are using Arduino’s internal pull-up resistors.

Click on the Help menu in the Arduino IDE.

Then click on Reference.

This opens an offline page in your browser.

Scroll down.

Click on INPUT_PULLUP.

ICpin2 and ICpin7 are set to OUTPUT mode to drive the motor.

analogRead command will read the analog value from the potentiometer.

This value will be given to analog pin A0.

Depending upon the potentiometer value, the speed of the motor will vary.

map command will convert the analog value to digital.

fwdbuttonState and bckbuttonState will fetch the signal if push button is pressed.

This enables the motor to rotate in a clockwise or anti-clockwise direction.

{

digitalWrite(ICpin2, LOW);

digitalWrite(ICpin7, LOW);

}

}

Then the else command ensures the motor is in OFF condition.

This code is available in the Code file link of this tutorial

You can download and use it.

Now click on upload button to upload the current program on Arduino.

DC_motor_output.mp4

I’ll press the push button connected to pin 13.

We can see the motor rotating in the clockwise direction.

Now I will release the push button.

The motor will stop rotating and it will be in OFF state.

Now again, I’ll press the push button connected to pin 12.

We can see the motor is rotating in anti-clockwise direction.

We can change the speed of motor by adjusting the potentiometer connected at A0.

Summary

• Pulse Width modulation
• PWM Duty Cycle
• PWM Frequency and
• How to control speed and direction of DC motor.

Assignment

Buzzer_output.mp4

• Connect a Buzzer instead of LED in the above circuit connection.
• Upload the same program and check the output.
• You would hear a noise with different frequencies.

About Spoken Tutorial project

Please download and watch it.

Spoken Tutorial workshops

For more details, please write to us.

Forum for specific questions

Acknowledgement

And this is Saurabh signing off.

Thanks for joining.