DC motor with transistor driver in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Arduino sketch controlling a DC motor speed?

Consider this Arduino code snippet that uses PWM to control a DC motor speed through a transistor driver. What will be the motor speed value printed on the serial monitor?

Arduino

const int motorPin = 9;
int speed = 128;

void setup() {
  pinMode(motorPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  analogWrite(motorPin, speed);
  Serial.println(speed);
  delay(1000);
}

A 64

B 255

C 128

D 0

💡 Hint

Look at the value assigned to speed and what is printed.

The variable speed is set to 128 and printed directly. The motor speed is controlled by PWM with this value.

🧠 Conceptual

intermediate

Which component protects the transistor from voltage spikes when the motor stops?

In a DC motor driver circuit using a transistor, which component is essential to protect the transistor from voltage spikes generated by the motor's inductive load?

A Capacitor

B LED

C Resistor

D Flyback diode

💡 Hint

Think about what happens when the motor suddenly stops and the transistor switches off.

The flyback diode provides a path for the current generated by the motor's inductance, preventing high voltage spikes that can damage the transistor.

🔧 Debug

advanced

Why does this Arduino code fail to run the motor at full speed?

Analyze the following Arduino code intended to run a DC motor at full speed using a transistor driver. Identify the reason the motor does not run at full speed.

Arduino

const int motorPin = 9;

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

void loop() {
  analogWrite(motorPin, 256);
  delay(1000);
}

A PWM value 256 is invalid; max is 255

B Pin 9 cannot output PWM

C Missing digitalWrite to turn motor on

D Delay is too short to see effect

💡 Hint

Check the valid range for PWM values in Arduino.

Arduino PWM values must be between 0 and 255. Using 256 causes unexpected behavior or no output.

📝 Syntax

advanced

Which option fixes the syntax error in this transistor driver control code?

Identify the correct syntax to set the transistor control pin as output and turn the motor on.

Arduino

int motorPin = 8

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

A Add semicolons after variable declaration and pinMode line

B Change pinMode to pinmode and add semicolon after digitalWrite

C Replace int with const int and remove digitalWrite line

D Add parentheses after motorPin declaration

💡 Hint

Look carefully at missing punctuation in Arduino C++ code.

Arduino code requires semicolons after statements. Missing semicolons cause syntax errors.

🚀 Application

expert

How many PWM steps are possible controlling the motor speed with analogWrite on Arduino?

Using analogWrite() on an Arduino to control a transistor-driven DC motor, how many distinct speed levels can you set?

A 1024

B 256

C 128

D 512

💡 Hint

Recall the resolution of Arduino's 8-bit PWM.

Arduino's analogWrite() uses 8-bit PWM, allowing 256 distinct levels (0 to 255).