DC motor with transistor driver in Arduino - Step-by-Step Execution

Concept Flow - DC motor with transistor driver

Start

↓

Set pinMode for transistor control pin

↓

Loop start

↓

Write HIGH to transistor pin -> Motor ON

↓

Delay for motor run time

↓

Write LOW to transistor pin -> Motor OFF

↓

Delay for motor stop time

↩Back to Loop start

The program sets a pin to control the transistor, then repeatedly turns the motor on and off with delays.

Execution Sample

Arduino

int motorPin = 9;

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

void loop() {
  digitalWrite(motorPin, HIGH); // Motor ON
  delay(1000);                  // Run 1 sec
  digitalWrite(motorPin, LOW);  // Motor OFF
  delay(1000);                  // Stop 1 sec
}

This code turns a DC motor on for 1 second, then off for 1 second, repeatedly using a transistor driver.

Execution Table

Step	Action	Pin State	Motor State	Delay(ms)
1	Setup: pinMode(motorPin, OUTPUT)	LOW (default)	OFF	0
2	Loop start: digitalWrite(motorPin, HIGH)	HIGH	ON	0
3	Delay(1000)	HIGH	ON	1000
4	digitalWrite(motorPin, LOW)	LOW	OFF	0
5	Delay(1000)	LOW	OFF	1000
6	Loop repeats from step 2	LOW	OFF	0

💡 Loop runs forever; motor toggles ON and OFF every 1 second.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6 (Loop)
motorPin	9	9	9	9
Pin State	LOW	HIGH	LOW	HIGH (next loop)
Motor State	OFF	ON	OFF	ON (next loop)

Key Moments - 3 Insights

Why do we set pinMode to OUTPUT in setup()?

Because in execution_table step 1, setting pinMode to OUTPUT allows the Arduino to control the transistor pin voltage to turn the motor ON or OFF.

What happens if we skip digitalWrite(motorPin, LOW)?

As shown in execution_table step 4, without setting LOW, the motor would stay ON continuously, not turning OFF between cycles.

Why do we use delay(1000) after turning motor ON and OFF?

Delays in steps 3 and 5 keep the motor running or stopped for 1 second each, making the ON/OFF visible and controlled.

Visual Quiz - 3 Questions

Look at the execution_table, what is the motor state at step 3?

A OFF

B ON

C Starting

D Undefined

💡 Hint

Check the 'Motor State' column at step 3 in the execution_table.

At which step does the transistor pin go LOW to turn the motor OFF?

A Step 4

B Step 2

C Step 3

D Step 5

💡 Hint

Look for 'digitalWrite(motorPin, LOW)' in the Action column of execution_table.

If delay(1000) after turning motor ON is changed to delay(2000), what changes in the execution_table?

A Motor State changes to OFF at step 3

B Pin State changes to LOW at step 3

C Delay at step 3 changes to 2000 ms

D No change in delay values

💡 Hint

Check the Delay(ms) column at step 3 and imagine increasing the delay time.

Concept Snapshot

Arduino controls a DC motor via a transistor by setting a digital pin HIGH or LOW.
Use pinMode(pin, OUTPUT) in setup to prepare the pin.
Turn motor ON with digitalWrite(pin, HIGH), OFF with digitalWrite(pin, LOW).
Use delay(ms) to keep motor ON or OFF for visible time.
Loop repeats to toggle motor continuously.

Full Transcript

This example shows how an Arduino controls a DC motor using a transistor driver. First, the motor control pin is set as an OUTPUT in setup. Then, in the loop, the pin is set HIGH to turn the motor ON, followed by a delay of 1 second to keep it running. Next, the pin is set LOW to turn the motor OFF, followed by another 1 second delay. This cycle repeats forever, making the motor turn ON and OFF every second. The execution table tracks each step, showing pin states and motor states. Key points include setting pinMode to OUTPUT, using digitalWrite to control the transistor, and using delay to control timing.