Motor speed control with PWM in Arduino - Mini Project: Build & Apply

Motor speed control with PWM

📖 Scenario: You have a small DC motor connected to an Arduino. You want to control its speed smoothly using PWM (Pulse Width Modulation). This is like adjusting the brightness of a lamp by changing how long it stays on and off quickly.

🎯 Goal: Build a simple Arduino program that sets up the motor pin, defines a speed value, uses PWM to control the motor speed, and prints the speed to the Serial Monitor.

📋 What You'll Learn

Use pin 9 for the motor control output

Create a variable called motorPin and set it to 9

Create a variable called speed and set it to 128 (half speed)

Use analogWrite() to send the speed value to the motor pin

Print the speed value to the Serial Monitor using Serial.println()

💡 Why This Matters

🌍 Real World

Controlling motor speed with PWM is common in robotics, fans, and toys where smooth speed control is needed.

💼 Career

Understanding PWM and motor control is important for embedded systems engineers and anyone working with hardware and electronics.

1

Set up the motor pin

Create an integer variable called motorPin and set it to 9. Then, in the setup() function, set motorPin as an output using pinMode(). Also, start the serial communication at 9600 baud with Serial.begin(9600).

Arduino

int motorPin = 9;

void setup() {
  // Set motorPin as output
  // Start serial communication at 9600 baud
  // Your code here
}

void loop() {
  // Your code here
}

Hint

Use pinMode(motorPin, OUTPUT); inside setup() to prepare the pin for output. Use Serial.begin(9600); to start serial communication.

2

Define the motor speed

Create an integer variable called speed and set it to 128 (which is about half speed). Add this variable above the setup() function.

Arduino

int motorPin = 9;
int speed = 128;  // Set motor speed to half

void setup() {
  pinMode(motorPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Your code here
}

Hint

Declare int speed = 128; before setup() so it can be used anywhere in the program.

3

Control the motor speed with PWM

Inside the loop() function, use analogWrite() to send the speed value to motorPin. This will control the motor speed using PWM.

Arduino

int motorPin = 9;
int speed = 128;

void setup() {
  pinMode(motorPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Send PWM signal to motorPin with speed value
  // Your code here
}

Hint

Use analogWrite(motorPin, speed); inside loop() to control motor speed.

4

Print the motor speed to Serial Monitor

Still inside the loop() function, add a line to print the speed value to the Serial Monitor using Serial.println(speed);. This helps you see the speed value on your computer.

Arduino

int motorPin = 9;
int speed = 128;

void setup() {
  pinMode(motorPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  analogWrite(motorPin, speed);
  // Print speed value to Serial Monitor
  // Your code here
}

Hint

Use Serial.println(speed); to print the speed value so you can see it on your computer screen.

Practice

1. What does PWM do in motor speed control on an Arduino?

easy

A. It changes the motor's voltage permanently.

B. It switches power on and off quickly to control speed.

C. It changes the motor's direction.

D. It measures the motor's speed.

Solution

1. Step 1: Understand PWM function

   PWM (Pulse Width Modulation) controls speed by rapidly switching power on and off.

2. Step 2: Compare options

   Only It switches power on and off quickly to control speed. correctly describes PWM's role in speed control, others describe different functions.

3. Final Answer:

   It switches power on and off quickly to control speed. -> Option B

4. Quick Check:

   PWM controls speed by switching power on/off [OK]

Hint: PWM controls speed by fast power switching [OK]

Common Mistakes:

• Thinking PWM changes voltage permanently
• Confusing speed control with direction control
• Believing PWM measures speed

2. Which Arduino function is used to set motor speed with PWM?

easy

A. pinMode(pin, OUTPUT)

B. digitalWrite(pin, value)

C. analogWrite(pin, value)

D. delay(value)

Solution

1. Step 1: Identify PWM function

   analogWrite(pin, value) sets PWM signal on a pin with value 0-255 controlling speed.

2. Step 2: Check other functions

   digitalWrite sets HIGH/LOW only, pinMode sets pin mode, delay pauses code; none control PWM speed.

3. Final Answer:

   analogWrite(pin, value) -> Option C

4. Quick Check:

   Use analogWrite for PWM speed control [OK]

Hint: Use analogWrite to set PWM speed value [OK]

Common Mistakes:

• Using digitalWrite instead of analogWrite
• Confusing pinMode with speed control
• Trying to use delay to control speed

3. What will be the motor speed if the code runs

analogWrite(9, 128);

?

medium

A. Motor runs at full speed

B. Motor is off

C. Motor runs at double speed

D. Motor runs at about half speed

Solution

1. Step 1: Understand PWM value range

   analogWrite value ranges 0 (off) to 255 (full speed). 128 is about half of 255.

2. Step 2: Interpret speed from value

   Value 128 means roughly half the power, so motor runs at about half speed.

3. Final Answer:

   Motor runs at about half speed -> Option D

4. Quick Check:

   128/255 ≈ half speed [OK]

Hint: PWM 128 means about half speed [OK]

Common Mistakes:

• Thinking 128 means full speed
• Assuming motor is off at 128
• Believing speed can be doubled

4. Identify the error in this code snippet for motor speed control:

int speed = 300;
analogWrite(6, speed);

medium

A. Speed value is out of PWM range (0-255).

B. Pin 6 cannot be used for PWM.

C. analogWrite requires three arguments.

D. Variable speed must be declared as float.

Solution

1. Step 1: Check PWM value limits

   analogWrite accepts values from 0 to 255. 300 is outside this range.

2. Step 2: Verify other options

   Pin 6 supports PWM, analogWrite takes two arguments, and int is fine for speed.

3. Final Answer:

   Speed value is out of PWM range (0-255). -> Option A

4. Quick Check:

   PWM value must be 0-255 [OK]

Hint: PWM values must be 0 to 255 only [OK]

Common Mistakes:

• Using values above 255 for PWM
• Thinking analogWrite needs 3 arguments
• Believing PWM pins are limited incorrectly

5. You want to smoothly increase motor speed from 0 to full over 5 seconds using PWM on pin 10. Which code snippet achieves this?

hard

A. for(int speed=0; speed<=255; speed++) { analogWrite(10, speed); delay(20); }

B. analogWrite(10, 255); delay(5000); analogWrite(10, 0);

C. for(int speed=255; speed>=0; speed--) { analogWrite(10, speed); delay(20); }

D. digitalWrite(10, HIGH); delay(5000); digitalWrite(10, LOW);

Solution

1. Step 1: Understand smooth speed increase

   Gradually increasing PWM value from 0 to 255 in small steps with delay creates smooth speed change.

2. Step 2: Analyze code snippets

   for(int speed=0; speed<=255; speed++) { analogWrite(10, speed); delay(20); } uses a for loop from 0 to 255 with delay(20)ms, totaling about 5 seconds. Others either jump speed or use digitalWrite which is not PWM.

3. Final Answer:

   for(int speed=0; speed<=255; speed++) { analogWrite(10, speed); delay(20); } -> Option A

4. Quick Check:

   Gradual PWM increase with delay = smooth speed [OK]

Hint: Use for loop with analogWrite and delay for smooth speed [OK]

Common Mistakes:

• Using digitalWrite instead of analogWrite
• Jumping speed without gradual steps
• Not using delay to slow speed change