Motor speed control with PWM in Arduino - Step-by-Step Execution

Concept Flow - Motor speed control with PWM

Start

↓

Setup PWM Pin

↓

Set PWM Value (0-255)

↓

Write PWM to Motor Pin

↓

Motor Speed Changes

↓

Loop or Update PWM

↩Back to Set PWM Value

The program sets up a PWM pin, writes a value between 0 and 255 to control motor speed, then loops to update speed as needed.

Execution Sample

Arduino

int motorPin = 9;
void setup() {
  pinMode(motorPin, OUTPUT);
}
void loop() {
  analogWrite(motorPin, 128); // half speed
}

This code sets motorPin as output and writes a PWM value of 128 to run the motor at half speed.

Execution Table

Step	Action	PWM Value	Motor Speed Effect
1	Setup motorPin as OUTPUT	N/A	Motor ready to receive PWM
2	Write PWM value 128 to motorPin	128	Motor runs at about 50% speed
3	Loop repeats, PWM stays 128	128	Motor speed remains steady
4	If PWM changes (e.g., 255)	255	Motor runs at full speed
5	If PWM changes (e.g., 0)	0	Motor stops
6	End of loop iteration	N/A	Ready for next PWM update

💡 Loop runs continuously; motor speed updates whenever PWM value changes

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 5	Final
motorPin	9	9	9	9	9
PWM Value	N/A	128	255	0	0

Key Moments - 3 Insights

Why does the motor speed change when PWM value changes?

Because PWM value controls the power sent to the motor; higher PWM means more power and faster speed (see execution_table steps 2, 4, 5).

What happens if PWM value is 0?

The motor stops because no power is sent (execution_table step 5 shows PWM 0 means motor speed stops).

Why do we use analogWrite instead of digitalWrite?

analogWrite sends a PWM signal to control speed smoothly, while digitalWrite only turns motor fully ON or OFF.

Visual Quiz - 3 Questions

Look at the execution_table, what PWM value makes the motor run at half speed?

A 128

B 255

C 0

D 64

💡 Hint

Check step 2 in the execution_table where PWM value 128 corresponds to half speed

At which step does the motor stop running?

A Step 2

B Step 4

C Step 5

D Step 3

💡 Hint

Look at step 5 in execution_table where PWM is 0 and motor speed stops

If PWM value changes from 128 to 255, what happens to motor speed?

A Motor speed stays the same

B Motor speed increases to full speed

C Motor speed decreases

D Motor stops

💡 Hint

See step 4 in execution_table where PWM 255 means full speed

Concept Snapshot

Motor speed control with PWM:
- Use analogWrite(pin, value) where value is 0-255
- 0 means motor off, 255 means full speed
- PWM controls power by switching ON/OFF rapidly
- Setup pin as OUTPUT before writing PWM
- Loop to update speed dynamically

Full Transcript

This example shows how to control motor speed using PWM on an Arduino. First, the motor pin is set as an output. Then, analogWrite sends a PWM signal with a value between 0 and 255. A value of 128 runs the motor at half speed, 255 at full speed, and 0 stops the motor. The loop repeats to keep the motor running or update speed. PWM controls motor power by turning the pin on and off quickly, changing the average voltage and thus speed.

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