DC motor with transistor driver in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the motor pin as an output.

Arduino

const int motorPin = 9;

void setup() {
  pinMode([1], OUTPUT);
}

void loop() {
  // Motor control code here
}

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

AINPUT

BmotorPin

C9

DpinMode

Attempts:

3 left

💡 Hint

Common Mistakes

Using the number 9 directly instead of the variable name.

Using INPUT instead of OUTPUT.

You need to tell the Arduino that motorPin is an output pin using pinMode().

2fill in blank

medium

Complete the code to turn the motor ON by setting the pin HIGH.

Arduino

const int motorPin = 9;

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

void loop() {
  digitalWrite(motorPin, [1]);
  delay(1000);
  digitalWrite(motorPin, LOW);
  delay(1000);
}

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

AHIGH

BLOW

COUTPUT

DINPUT

Attempts:

3 left

💡 Hint

Common Mistakes

Using LOW instead of HIGH to turn the motor ON.

Confusing pinMode values with digitalWrite values.

To turn the motor ON, set the pin to HIGH using digitalWrite().

3fill in blank

hard

Fix the error in the code to correctly control the motor speed using PWM.

Arduino

const int motorPin = 9;

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

void loop() {
  analogWrite(motorPin, [1]);
  delay(1000);
}

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

AOUTPUT

BHIGH

C255

DdigitalWrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using HIGH instead of a numeric PWM value.

Using digitalWrite instead of analogWrite.

Use analogWrite() with a value between 0 and 255 to control motor speed. 255 means full speed.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps motor speeds to their PWM values if speed is greater than 100.

Arduino

int speeds[] = {50, 120, 200};

void setup() {
  // This is a conceptual example, Arduino C++ does not support dictionary comprehensions
  // Imagine a map: {speed: [1] for speed in speeds if speed [2] 100}
}

void loop() {}

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

Aspeed * 2

B<

C>

Dspeed + 10

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the condition.

Using incorrect expressions for the value.

The comprehension maps each speed to speed * 2 only if the speed is greater than 100.

5fill in blank

hard

Fill all three blanks to create a function that sets motor speed only if the speed is within 0 to 255.

Arduino

const int motorPin = 9;

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

void setMotorSpeed(int speed) {
  if (speed [1] 0 && speed [2] 255) {
    analogWrite(motorPin, [3]);
  }
}

void loop() {
  setMotorSpeed(200);
}

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

A>=

B<=

Cspeed

DmotorPin

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators.

Passing motorPin instead of speed to analogWrite.

The function checks if speed is between 0 and 255 inclusive, then writes the speed value to the motor pin.

Practice

1. What is the main role of a transistor when controlling a DC motor with an Arduino?

easy

A. To act as a switch that controls the motor safely

B. To increase the motor speed directly

C. To power the Arduino board

D. To measure the motor's temperature

Solution

1. Step 1: Understand transistor function

   A transistor acts like a switch or amplifier in circuits.

2. Step 2: Apply to motor control

   In Arduino motor control, the transistor switches the motor on/off safely without damaging the board.

3. Final Answer:

   To act as a switch that controls the motor safely -> Option A

4. Quick Check:

   Transistor = switch for motor control [OK]

Hint: Think of transistor as a safe on/off switch for the motor [OK]

Common Mistakes:

• Confusing transistor with motor speed controller
• Thinking transistor powers the Arduino
• Assuming transistor measures anything

2. Which Arduino code snippet correctly sets a transistor pin to control a DC motor?

easy

A. pinMode(9, INPUT); digitalRead(9);

B. pinMode(9, INPUT); digitalWrite(9, HIGH);

C. pinMode(9, OUTPUT); digitalRead(9);

D. pinMode(9, OUTPUT); digitalWrite(9, HIGH);

Solution

1. Step 1: Set pin as output for controlling transistor

   To control a transistor, the Arduino pin must be OUTPUT.

2. Step 2: Write HIGH to turn motor on

   digitalWrite(9, HIGH) sends voltage to transistor base to switch motor on.

3. Final Answer:

   pinMode(9, OUTPUT); digitalWrite(9, HIGH); -> Option D

4. Quick Check:

   Output pin + HIGH = motor ON [OK]

Hint: Use OUTPUT mode and digitalWrite to control transistor [OK]

Common Mistakes:

• Setting pin as INPUT when controlling transistor
• Using digitalRead instead of digitalWrite
• Not setting pinMode before writing

3. What will be the effect of this Arduino code controlling a transistor connected to a DC motor?

int motorPin = 9;
void setup() {
  pinMode(motorPin, OUTPUT);
}
void loop() {
  analogWrite(motorPin, 128);
  delay(2000);
  analogWrite(motorPin, 0);
  delay(2000);
}

medium

A. Motor runs at half speed for 2 seconds, then stops for 2 seconds repeatedly

B. Motor runs at full speed continuously

C. Motor never runs because analogWrite is wrong

D. Motor runs at full speed for 2 seconds, then stops for 2 seconds repeatedly

Solution

1. Step 1: Understand analogWrite value

   analogWrite with 128 sets PWM to about 50% duty cycle, so motor runs at half speed.

2. Step 2: Analyze timing in loop

   Motor runs at half speed for 2 seconds, then analogWrite(0) stops motor for 2 seconds, repeating.

3. Final Answer:

   Motor runs at half speed for 2 seconds, then stops for 2 seconds repeatedly -> Option A

4. Quick Check:

   analogWrite(128) = half speed [OK]

Hint: PWM 128 means half speed, 0 means stop [OK]

Common Mistakes:

• Thinking analogWrite(128) is full speed
• Confusing analogWrite with digitalWrite
• Ignoring delay timing effects

4. Identify the error in this Arduino code controlling a transistor for a DC motor:

int motorPin = 9;
void setup() {
  pinMode(motorPin, INPUT);
}
void loop() {
  digitalWrite(motorPin, HIGH);
}

medium

A. Pin number 9 cannot be used for motor control

B. Pin is set as INPUT but digitalWrite is used

C. digitalWrite should be digitalRead

D. Missing delay in loop

Solution

1. Step 1: Check pinMode for transistor control

   Pin controlling transistor must be OUTPUT, not INPUT.

2. Step 2: Identify conflict with digitalWrite

   digitalWrite on an INPUT pin causes undefined behavior or no effect.

3. Final Answer:

   Pin is set as INPUT but digitalWrite is used -> Option B

4. Quick Check:

   OUTPUT needed for digitalWrite [OK]

Hint: Set pinMode to OUTPUT before digitalWrite [OK]

Common Mistakes:

• Using INPUT mode with digitalWrite
• Confusing digitalWrite with digitalRead
• Ignoring pinMode setup

5. You want to control a DC motor speed using PWM on pin 9 with a transistor driver. Which additional component is essential to protect your circuit from voltage spikes caused by the motor?

hard

A. An LED connected in parallel with the transistor

B. A capacitor connected to the Arduino 5V pin

C. A diode connected across the motor terminals

D. A resistor in series with the motor

Solution

1. Step 1: Understand motor voltage spikes

   When motor stops suddenly, it can create voltage spikes that damage components.

2. Step 2: Identify protection method

   A diode placed across motor terminals (flyback diode) safely redirects spikes, protecting transistor and Arduino.

3. Final Answer:

   A diode connected across the motor terminals -> Option C

4. Quick Check:

   Flyback diode protects circuit from spikes [OK]

Hint: Always add diode across motor for spike protection [OK]

Common Mistakes:

• Skipping diode and risking transistor damage
• Using resistor instead of diode for spike protection
• Confusing capacitor or LED as spike protection