How Does Serial Communication Works in Arduino

Serial communication is a fundamental aspect of microcontroller programming, and it plays a crucial role in enabling devices to exchange information. In the world of Arduino, serial communication is a powerful tool that allows you to send and receive data between your Arduino board and other devices, such as computers, sensors, displays, and more. In this article, How Does Serial Communication Works in Arduino, I will be covering everything from the basics to advanced techniques.

What is Serial Communication?

Serial communication is a method of transmitting data one bit at a time over a communication channel, as opposed to parallel communication, where multiple bits are sent simultaneously. It is a fundamental concept in electronics and computing and is used in a wide range of applications, including Arduino projects.

In serial communication, data is sent sequentially, usually as a stream of binary digits (0s and 1s). This method allows for reliable and efficient data transmission over long distances and between different devices. Serial communication can be either synchronous (data is sent at a constant rate, synchronized by a clock signal) or asynchronous (data is sent without a clock signal and relies on agreed-upon timing parameters).

Why is Serial Communication Important in Arduino?

Arduino boards are often used in projects that require communication with external devices or computers. Serial communication provides a straightforward way to exchange information between an Arduino and other components. Some key reasons why serial communication is crucial in Arduino include:

  • Sensor Integration: Many sensors and modules used with Arduino communicate via serial protocols. This allows you to collect data from various sensors and process it on your Arduino board.

  • External Control: Serial communication enables you to control your Arduino from a computer or another microcontroller. This is essential for remote monitoring and control applications.

  • Debugging and Monitoring: Serial communication provides a way to send debugging information and monitor the operation of your Arduino code, making it easier to identify and fix issues.

Types of Serial Communication in Arduino

Arduino supports various types of serial communication, including:

  • UART (Universal Asynchronous Receiver/Transmitter): This is the most common form of serial communication used in Arduino. UART communication is asynchronous and is typically used for communication between the Arduino board and other microcontrollers, sensors, and modules.

  • I2C (Inter-Integrated Circuit): I2C is a synchronous serial communication protocol that allows multiple devices to communicate over a shared bus. It is commonly used for connecting sensors and displays to Arduino.

  • SPI (Serial Peripheral Interface): SPI is another synchronous serial communication protocol that is used for high-speed communication between Arduino and devices like displays, memory chips, and other microcontrollers.

Serial Ports

  • Hardware Serial Ports: Arduino boards typically have one or more hardware serial ports built-in. These hardware serial ports are dedicated pins on the microcontroller that provide easy and reliable serial communication. Common hardware serial ports on Arduino boards include “Serial” (on the Arduino Uno) and “Serial1,” “Serial2,” etc. (on boards with multiple serial ports like the Arduino Mega).
  • Software Serial Ports: In addition to hardware serial ports, Arduino also provides a software serial library that allows you to create additional virtual serial ports using any available digital pins. This is useful when you need more than one serial communication channel or when you want to use pins other than the default hardware serial pins.

When selecting a serial port for your project, consider the following factors:

  • Hardware vs. Software Serial: Hardware serial ports are generally more reliable and have better performance compared to software serial. Use hardware serial when available and reserve software serial for cases where extra ports are needed.

  • Pin Availability: Ensure that the pins used by the selected serial port do not conflict with other components or functions in your project.

  • Baud Rate: Different serial ports may support different baud rates, so choose one that matches the requirements of your project.

  • Serial Port Compatibility: Some Arduino boards have multiple hardware serial ports, while others have only one. Make sure your choice aligns with the capabilities of your specific Arduino board.

Serial Communication Modes 

UART (Universal Asynchronous Receiver/Transmitter): UART is the most common form of serial communication used in Arduino. It is asynchronous, which means that data is sent without a shared clock signal. Instead, both the sender and receiver agree on a set of parameters to determine the data rate and timing.

How Does Serial Communication Work in Arduino - UART
Credits: peppe8o

The key parameters in UART communication are:

  • Baud Rate: This defines the data transmission speed in bits per second (bps). Both the transmitter and receiver must use the same baud rate for successful communication.

  • Data Bits: The number of data bits in each byte of data. Common values are 8 bits, 7 bits, or 6 bits.

  • Stop Bits: Stop bits indicate the end of a data byte. Common values are 1 or 2 stop bits.

  • Parity: Parity bits are optional and can be used for error checking. Common options are no parity, even parity, or odd parity.

Baud Rate

The baud rate determines how quickly data is transmitted over the serial communication channel. It is specified in bits per second (bps). Common baud rates used in Arduino projects include 9600, 19200, 38400, and 115200 bps. Both the sender and receiver must use the same baud rate to communicate successfully.

Choosing the appropriate baud rate depends on factors such as the hardware capabilities of your devices and the required data transfer speed. Higher baud rates allow for faster data transfer but may require more precise timing and can be susceptible to noise and errors over longer distances.

Data Bits, Stop Bits, and Parity

In UART communication, each data byte typically consists of the following components:

  • Data Bits: The actual data being transmitted, usually 8 bits in Arduino communication.
  • Start Bit: A single start bit indicates the beginning of the data byte.
  • Stop Bit(s): One or two stop bits indicate the end of the data byte.
  • Parity Bit (Optional): An optional parity bit can be used for error checking. It can be set to even, odd, or none.

The combination of data bits, start bits, stop bits, and parity settings forms the frame format for UART communication. Both the transmitter and receiver must use the same frame format to interpret the data correctly.

Half-Duplex vs. Full-Duplex Communication

UART communication can be categorized into two main modes: half-duplex and full-duplex.

  • Half-Duplex: In half-duplex communication, data can be transmitted in both directions, but not simultaneously. The communication channel switches between sending and receiving modes. This is common in scenarios where devices take turns transmitting and receiving data.

  • Full-Duplex: Full-duplex communication allows data to be transmitted simultaneously in both directions. This requires two separate communication channels, one for transmitting and one for receiving. Hardware serial ports on Arduino boards support full-duplex communication.

Setting Up Serial Communication

Now that we have a foundational understanding of serial communication in Arduino, let’s explore how to set up and configure serial communication for your projects.

How Does Serial Communication Work in Arduino - Setting Up Arduino Uno
Credits: electronicshub
  • Hardware Setup

Setting up hardware serial communication is straightforward on Arduino boards with built-in serial ports. Here are the basic steps:

  1. Identify the hardware serial pins on your Arduino board. These pins are labeled “TX” (transmit) and “RX” (receive) and are usually found near the edge of the board.

  2. Connect the “TX” pin of your Arduino to the “RX” pin of the device you want to communicate with, and vice versa. Ensure that you have a common ground connection between your Arduino and the other device.

  3. If you’re using a USB-to-Serial converter (e.g., an FTDI module) to connect your Arduino to a computer, connect the converter’s “TX” to the Arduino’s “RX” and the converter’s “RX” to the Arduino’s “TX.” Again, ensure that you have a common ground connection.

  4. Power your Arduino and the connected device or computer.

  • Software Setup

Setting up serial communication in software involves configuring the serial port with the appropriate settings. Here’s how you can do it in an Arduino sketch:

void setup() {
// Initialize serial communication
Serial.begin(9600); // Replace with your desired baud rate

void loop() {
// Your code here

In the code above:

  • Serial.begin() initializes the serial communication with a specific baud rate. Replace 9600 with the baud rate you intend to use.

Now, your Arduino is ready to send and receive data over the serial port.

  • Serial Monitor in the Arduino IDE

The Arduino IDE includes a built-in Serial Monitor tool that allows you to send and receive serial data between your Arduino and your computer. To use the Serial Monitor:

  1. Open the Arduino IDE.

  2. Write your Arduino sketch, including the necessary Serial.begin() configuration.

  3. Click on the “Serial Monitor” icon in the top-right corner of the IDE (or go to “Tools” > “Serial Monitor”).

  4. The Serial Monitor window will open, and you can start sending and receiving data.

You can use the Serial Monitor for debugging, monitoring sensor data, and interacting with your Arduino in real-time.

  • Sending and Receiving Data

Now that we’ve set up the serial communication, let’s explore how to send and receive data using Arduino.

Arduino provides several functions for sending data over the serial port, including Serial.write() and Serial.print(). Here’s how to use them:

  • Serial.write(): This function sends binary data as bytes. You can use it to send raw data, such as sensor readings or binary commands.

byte dataByte = 42;

  • Serial.print(): This function converts data to a human-readable ASCII representation and sends it as text. It’s useful for sending text-based messages and numbers.

int sensorValue = analogRead(A0);
Serial.print(“Sensor value: “);

  • Serial.read() and Serial.available()

To receive data, you can use the Serial.read() function to read a single byte of data from the serial buffer. You can also use Serial.available() to check if there is data available for reading. Here’s an example:

void loop() {
if (Serial.available() > 0) {
char receivedChar = Serial.read();
// Process the received character here
// Your code here

In the code above, we check if there is data available in the serial buffer using Serial.available(). If data is available, we use Serial.read() to read a single character (byte) and store it in the receivedChar variable. You can then process the received data as needed.

  • Serial.println()

Serial.println() is a convenient function for sending data with a newline character, which makes it suitable for sending multiple lines of text. For example:

void loop() {
Serial.println(“Hello, Arduino!”);
delay(1000); // Delay for 1 second

This code sends the “Hello, Arduino!” message to the serial port once every second.

  • Serial.flush()

Serial.flush() is used to wait for the transmission of outgoing serial data to complete. It’s often used to ensure that all data has been sent before proceeding with other operations in your code.

void loop() {
Serial.print(“Sending data…”);
Serial.flush(); // Wait for data to be sent
// Continue with other code

Serial Communication Examples

To illustrate how serial communication works in practice, let’s explore a few practical examples.

  • Sending Sensor Data to a Computer : Suppose you have a temperature sensor connected to your Arduino, and you want to send temperature readings to a computer for monitoring. Here’s a basic example:

void setup() {

void loop() {
float temperature = readTemperature(); // Function to read temperature
Serial.print(“Temperature: “);
Serial.println(” °C”);
delay(1000); // Send data every 1 second

float readTemperature() {
// Replace this with code to read temperature from your sensor
return 25.5; // Example temperature reading

In this example, the Arduino reads the temperature from the sensor, sends it to the computer over the serial port, and includes a delay to send data at a reasonable rate.

  • Controlling LEDs via Serial Commands: You can also control hardware components, such as LEDs, using serial commands from a computer. Here’s a simple example:

int ledPin = 13; // Pin connected to an LED

void setup() {
pinMode(ledPin, OUTPUT);

void loop() {
if (Serial.available() > 0) {
char command = Serial.read();
if (command == ‘1’) {
digitalWrite(ledPin, HIGH); // Turn the LED on
} else if (command == ‘0’) {
digitalWrite(ledPin, LOW); // Turn the LED off
// Your code here

In this example, when you send “1” from the Serial Monitor, it turns on the LED connected to pin 13, and when you send “0,” it turns the LED off.

  • Interfacing with External Modules

Serial communication can also be used to interface with external modules, such as GPS receivers, Bluetooth modules, and GSM modules. These modules often communicate with Arduino via UART and provide valuable data or enable wireless communication.

The specific setup and code for interfacing with external modules will depend on the module’s documentation and communication protocol.

Advanced Serial Communication

While the basics of serial communication are covered in the previous sections, there are advanced techniques and features you can explore to enhance your Arduino projects.

  • Serial Events

Arduino allows you to define custom functions that execute when specific characters or data patterns are received over the serial port. These are known as serial events. Here’s an example:

void setup() {
Serial.println(“Type ‘A’ for action A or ‘B’ for action B”);

void loop() {
if (Serial.available() > 0) {
char receivedChar = Serial.read();
if (receivedChar == ‘A’) {
} else if (receivedChar == ‘B’) {

void performActionA() {
// Code to execute when ‘A’ is received
Serial.println(“Action A performed”);

void performActionB() {
// Code to execute when ‘B’ is received
Serial.println(“Action B performed”);

In this example, the Arduino listens for ‘A’ or ‘B’ characters and executes corresponding actions when they are received.

Read also: How to Control LED From Windows PC Using Arduino – Serial Communication


Serial communication is a fundamental concept in Arduino programming, enabling data exchange between your Arduino board and other devices, sensors, and computers. By understanding the basics of serial communication, including UART, baud rates, data formats, and hardware setup, you can create versatile and interactive projects.

Whether you’re sending sensor data to a computer, controlling hardware components, interfacing with external modules, or exploring advanced serial techniques, serial communication in Arduino opens up a world of possibilities for your projects. As you continue to work with Arduino, you’ll find that mastering serial communication is a key skill that will help you build more complex and interconnected systems. So, roll up your sleeves, fire up your Arduino, and start communicating! I hope you like this blog post on How Does Serial Communication Works in Arduino.

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