Motor speed control with PWM in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does PWM stand for in motor speed control?

PWM stands for Pulse Width Modulation. It controls motor speed by changing the amount of time the power is ON versus OFF.

beginner

How does PWM control the speed of a DC motor?

PWM changes the motor's speed by adjusting the duty cycle, which is the percentage of time the signal is HIGH in each cycle. More HIGH time means faster motor speed.

beginner

Which Arduino function is used to generate a PWM signal?

The Arduino function analogWrite(pin, value) generates a PWM signal on the specified pin. The value ranges from 0 (always OFF) to 255 (always ON).

intermediate

Why can't we use analogWrite to get a true analog voltage?

Because analogWrite creates a digital PWM signal that switches ON and OFF rapidly. The motor or device averages this to behave like an analog voltage.

beginner

What is the typical range of PWM values for controlling motor speed on Arduino?

PWM values range from 0 to 255. 0 means motor is stopped, 255 means motor runs at full speed, and values in between control speed proportionally.

What does a PWM duty cycle of 50% mean for motor speed?

A Motor runs at full speed

B Motor runs at double speed

C Motor is stopped

D Motor runs at half speed

A 50% duty cycle means the power is ON half the time, so the motor runs roughly at half speed.

Which Arduino function is used to send a PWM signal to a motor?

A digitalWrite()

B analogWrite()

C pinMode()

D delay()

analogWrite() sends a PWM signal by varying the duty cycle.

What happens if you set PWM value to 0 on Arduino motor control?

A Motor runs at full speed

B Motor runs at half speed

C Motor stops

D Motor reverses direction

PWM value 0 means the signal is always OFF, so the motor stops.

Why is PWM preferred over a simple resistor to control motor speed?

A PWM provides efficient speed control without heat loss

B PWM wastes more power

C Resistors are cheaper

D PWM is slower to respond

PWM controls speed efficiently by switching power ON and OFF rapidly, reducing heat loss compared to resistors.

What is the maximum PWM value you can use with Arduino's analogWrite()?

A 255

B 1023

C 100

D 500

Arduino's analogWrite() uses values from 0 to 255 for PWM duty cycle.

Explain how PWM controls the speed of a DC motor using Arduino.

Think about how changing the time the motor gets power affects its speed.

Describe why PWM is more efficient than using a resistor to control motor speed.

Consider what happens to energy when power is switched ON and OFF quickly.

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