Why Motor speed control with PWM in Arduino? - Purpose & Use Cases

The Big Idea

What if you could control motor speed as smoothly as turning a dimmer switch on a lamp?

The Scenario

Imagine you want to control the speed of a motor by turning it on and off manually with a switch or button.

You try to adjust the speed by quickly flipping the switch faster or slower.

This feels like trying to control the volume of music by rapidly pressing the power button on and off.

The Problem

This manual way is very hard to do accurately.

Your hand can't flip the switch fast enough or consistently.

The motor speed jumps between full on and full off, causing jerky movement and wear.

It wastes energy and can damage the motor over time.

The Solution

PWM (Pulse Width Modulation) solves this by turning the motor on and off very fast at a steady rate.

It changes the ratio of ON time to OFF time to smoothly control speed.

This is like dimming a light by quickly flicking it on and off so fast your eyes see a steady glow.

Before vs After

✗ Before

digitalWrite(motorPin, HIGH);
delay(1000);
digitalWrite(motorPin, LOW);
delay(1000);

✓ After

analogWrite(motorPin, 128); // 50% speed using PWM

What It Enables

With PWM, you can smoothly and efficiently control motor speed with simple code and no extra hardware.

Real Life Example

Think of a remote-controlled car where you want to gently speed up or slow down instead of just full speed or stop.

PWM lets you do that easily, making the car drive smoothly and last longer.

Key Takeaways

Manual on/off control is jerky and unreliable for motor speed.

PWM uses fast switching to create smooth speed control.

This method saves energy and protects the motor.

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