DC motor with transistor driver in Arduino - Mini Project: Build & Apply

DC Motor Control with Transistor Driver

📖 Scenario: You have a small DC motor connected to an Arduino through a transistor driver. You want to control the motor speed by sending a PWM signal from the Arduino to the transistor base pin.This project will guide you step-by-step to write the Arduino code to control the motor speed.

🎯 Goal: Build an Arduino program that sets up the motor control pin, defines a speed value, sends the PWM signal to the transistor to control the motor speed, and prints the speed value to the Serial Monitor.

📋 What You'll Learn

Use pin 9 as the motor control pin connected to the transistor base

Define a variable called motorSpeed with the value 128

Use analogWrite to send the PWM signal to the motor control pin

Print the motor speed value to the Serial Monitor using Serial.println

💡 Why This Matters

🌍 Real World

Controlling DC motors with transistors is common in robotics and small electronics projects where you need to adjust motor speed safely.

💼 Career

Understanding how to control motors with microcontrollers and transistor drivers is a key skill for embedded systems and hardware engineers.

1

Set up the motor control pin

Write a line of code to create a variable called motorPin and set it to 9.

Arduino

# Define the motor control pin
# Your code here

Hint

Use int motorPin = 9; to assign pin 9 to the motorPin variable.

2

Define the motor speed variable

Add a line of code to create a variable called motorSpeed and set it to 128.

Arduino

int motorPin = 9;
// Define the motor speed
# Your code here

Hint

Use int motorSpeed = 128; to set the speed to half of the maximum PWM value.

3

Send PWM signal to control motor speed

Write the setup() function to set motorPin as an output. Then write the loop() function to use analogWrite(motorPin, motorSpeed); to send the PWM signal.

Arduino

int motorPin = 9;
int motorSpeed = 128;

void setup() {
  // Set motorPin as output
  // Your code here
}

void loop() {
  // Send PWM signal to motorPin
  // Your code here
}

Hint

Use pinMode(motorPin, OUTPUT); in setup() and analogWrite(motorPin, motorSpeed); in loop().

4

Print motor speed to Serial Monitor

Add a line inside the loop() function to print the value of motorSpeed to the Serial Monitor using Serial.println(motorSpeed);.

Arduino

int motorPin = 9;
int motorSpeed = 128;

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

void loop() {
  analogWrite(motorPin, motorSpeed);
  // Print motorSpeed to Serial Monitor
  // Your code here
}

Hint

Use Serial.println(motorSpeed); to print the speed. Add delay(1000); to slow down the output.

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