analogWrite() and PWM output in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the PWM output on pin 9 to half brightness.

Arduino

analogWrite(9, [1]);

Drag options to blanks, or click blank then click option'

A128

B255

C0

D512

Attempts:

3 left

💡 Hint

Common Mistakes

Using 512 which is out of range for analogWrite.

Using 255 which is full brightness, not half.

The value 128 sets the PWM duty cycle to about 50%, which is half brightness.

2fill in blank

medium

Complete the code to set pin 6 as an output before using analogWrite.

Arduino

pinMode(6, [1]);

Drag options to blanks, or click blank then click option'

AINPUT

BINPUT_PULLUP

COUTPUT

DPWM

Attempts:

3 left

💡 Hint

Common Mistakes

Using INPUT or INPUT_PULLUP which are for input pins.

Using PWM which is not a valid pinMode argument.

Pin 6 must be set as OUTPUT to use analogWrite for PWM output.

3fill in blank

hard

Fix the error in the code to correctly write PWM to pin 3.

Arduino

analogWrite([1], 200);

Drag options to blanks, or click blank then click option'

A3

B13

CA0

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using pin 13 which is digital only, no PWM.

Using analog pin A0 which does not support PWM output.

Pin 3 supports PWM output, so it is the correct pin to use with analogWrite.

4fill in blank

hard

Fill both blanks to create a PWM signal with 75% duty cycle on pin 10.

Arduino

pinMode(10, [1]);
analogWrite(10, [2]);

Drag options to blanks, or click blank then click option'

AOUTPUT

BINPUT

C191

D64

Attempts:

3 left

💡 Hint

Common Mistakes

Setting pinMode to INPUT instead of OUTPUT.

Using 64 which is about 25%, not 75%.

Pin 10 must be set as OUTPUT. A value of 191 (about 75% of 255) sets the PWM duty cycle to 75%.

5fill in blank

hard

Fill all three blanks to create a dictionary mapping pins to PWM values above 100.

Arduino

pwm_values = { [1]: [2] for [1] in [3, 5, 6] if [2] > 100 }

Drag options to blanks, or click blank then click option'

Apin

Bvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same variable name for both key and value.

Mixing up the variable names in the condition.

The dictionary comprehension uses 'pin' as the key variable and 'value' as the value variable. The condition checks if 'value' is greater than 100.

Practice

1. What does the analogWrite() function do on an Arduino board?

easy

A. It sets a digital pin to HIGH or LOW.

B. It reads the voltage from an analog sensor.

C. It outputs a PWM signal to simulate an analog voltage on a digital pin.

D. It measures the frequency of a signal on a pin.

Solution

1. Step 1: Understand the purpose of analogWrite()

   The analogWrite() function does not output a true analog voltage but uses PWM (Pulse Width Modulation) to simulate varying voltage levels on digital pins.

2. Step 2: Compare options with function behavior

   It outputs a PWM signal to simulate an analog voltage on a digital pin. correctly describes this behavior. Options A, B, and D describe other functions or actions unrelated to analogWrite().

3. Final Answer:

   It outputs a PWM signal to simulate an analog voltage on a digital pin. -> Option C

4. Quick Check:

   analogWrite() = PWM output [OK]

Hint: Remember: analogWrite() controls brightness/speed via PWM [OK]

Common Mistakes:

• Confusing analogWrite() with analogRead()
• Thinking analogWrite() outputs true analog voltage
• Assuming analogWrite() sets pin HIGH or LOW directly

2. Which of the following is the correct syntax to set pin 9 to half brightness using analogWrite()?

easy

A. analogWrite(9, 512);

B. analogWrite(9, 0);

C. analogWrite(9, 255);

D. analogWrite(9, 127);

Solution

1. Step 1: Understand the value range for analogWrite()

   The analogWrite() function accepts values from 0 to 255, where 0 is off and 255 is full brightness.

2. Step 2: Calculate half brightness value

   Half brightness is about half of 255, which is approximately 127. A uses 512 (out of range), B uses 0 (off), C uses 255 (full brightness), so D is correct.

3. Final Answer:

   analogWrite(9, 127); -> Option D

4. Quick Check:

   Half brightness ≈ 127 [OK]

Hint: Use values between 0-255; half is about 127 [OK]

Common Mistakes:

• Using values above 255 (like 512)
• Confusing digitalWrite() with analogWrite()
• Using full brightness value instead of half

3. What will be the effect of the following code snippet on an LED connected to pin 6?

void setup() {
  pinMode(6, OUTPUT);
}

void loop() {
  analogWrite(6, 0);
  delay(1000);
  analogWrite(6, 255);
  delay(1000);
}

medium

A. The LED will blink on and off every second.

B. The LED will stay dimly lit.

C. The LED will stay fully on.

D. The LED will flicker rapidly.

Solution

1. Step 1: Analyze analogWrite values and delays

   The code sets pin 6 to 0 (off) for 1 second, then to 255 (full brightness) for 1 second, repeatedly.

2. Step 2: Understand LED behavior

   When the pin is 0, the LED is off; when 255, it is fully on. The delays cause the LED to stay in each state for 1 second, making it blink on and off every second.

3. Final Answer:

   The LED will blink on and off every second. -> Option A

4. Quick Check:

   0 and 255 with delays = blink [OK]

Hint: 0 means off, 255 means full on; delays cause blinking [OK]

Common Mistakes:

• Thinking analogWrite(0) dims LED instead of off
• Ignoring delay effects on LED timing
• Assuming LED flickers rapidly without delay

4. Identify the error in this code snippet intended to fade an LED on pin 10:

void setup() {
  pinMode(10, OUTPUT);
}

void loop() {
  for (int i = 0; i <= 255; i++) {
    analogWrite(10, i);
    delay(10);
  }
  for (int i = 255; i >= 0; i--) {
    analogWrite(10, i);
    delay(10);
  }
}

medium

A. The code will work correctly and fade the LED in and out.

B. The for loop variable i should be declared outside the loop.

C. The pin 10 is not set as OUTPUT.

D. analogWrite() cannot be used with pin 10.

Solution

1. Step 1: Check pinMode setup

   Pin 10 is correctly set as OUTPUT in setup().

2. Step 2: Analyze the for loops and analogWrite usage

   The loops increase and then decrease the PWM value from 0 to 255 and back, with delays to create a smooth fade effect. This is a common and correct pattern.

3. Final Answer:

   The code will work correctly and fade the LED in and out. -> Option A

4. Quick Check:

   For loops with analogWrite create fade [OK]

Hint: For fading, increase then decrease PWM values smoothly [OK]

Common Mistakes:

• Forgetting to set pinMode to OUTPUT
• Thinking analogWrite can't be used on pin 10
• Misunderstanding loop variable scope

5. You want to control the speed of a DC motor using PWM on pin 3. Which code snippet correctly sets the motor speed to 60% power?

hard

A. analogWrite(3, 60); // 60 is the percentage value

B. analogWrite(3, 153); // 60% of 255 is about 153

C. analogWrite(3, 0.6); // decimal value for 60%

D. analogWrite(3, 255); // full power always

Solution

1. Step 1: Convert percentage to PWM value

   60% of the maximum PWM value 255 is 0.6 x 255 = 153.

2. Step 2: Check the analogWrite parameter

   analogWrite() requires an integer between 0 and 255. analogWrite(3, 153); // 60% of 255 is about 153 uses 153, which is correct. analogWrite(3, 60); // 60 is the percentage value uses 60 which is too low, C uses a decimal which is invalid, and D sets full power.

3. Final Answer:

   analogWrite(3, 153); // 60% of 255 is about 153 -> Option B

4. Quick Check:

   60% x 255 = 153 [OK]

Hint: Multiply percentage by 255 for PWM value [OK]

Common Mistakes:

• Passing percentage directly instead of scaled value
• Using decimal numbers instead of integers
• Always setting full power without scaling