Arduino Serial.print() & Serial.println() | Arduino Serial Monitor

In this tutorial, you’ll learn how to use the Arduino Serial.print() & Serial.println() Functions. We’ll discuss how the Arduino Serial.print() & Serial.println() functions work and how to use them to print various data types to the serial port.

We’ll also discuss how to use Arduino’s Serial Monitor For Debugging your Arduino projects. Without further ado, let’s get right into it!

Table of Contents

1. Arduino Serial.print() Function
2. Arduino Serial.println() Function
3. Arduino Serial Monitor
4. Arduino Serial Print String Example
5. Arduino Serial Print String & Variable Example
6. Arduino Serial Print Float & Double Example
7. Arduino Serial Print Hex & Binary Example
8. Wrap Up

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Arduino Serial.print() Function

The Serial.print() function is used to send data as human-readable text over the UART interface. It accepts various data types such as integers, floating-point numbers, strings, and characters. It allows you to display information, debug messages, or sensor readings in a readable format. The Serial.print() function does not append a newline character at the end.

This function can also take another optional argument that specifies the format.

Parameters

val: the value to print. Allowed data types: any data type.

format: format options are  BIN(binary, or base 2),  OCT(octal, or base 8),  DEC(decimal, or base 10),  HEX(hexadecimal, or base 16). For floating point numbers, this parameter specifies the number of decimal places to use. For example:

• Serial.print(78, BIN) gives “1001110”
• Serial.print(78, OCT) gives “116”
• Serial.print(78, DEC) gives “78”
• Serial.print(78, HEX) gives “4E”
• Serial.print(1.23456, 0) gives “1”
• Serial.print(1.23456, 2) gives “1.23”
• Serial.print(1.23456, 4) gives “1.2346”

Returns

Serial.print() returns the number of bytes written, though reading that number is optional. Data type:  size_t.

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Arduino Serial.println() Function

The Serial.println() function is similar to the Serial.print() function with only one difference which is following the printed text with a carriage return character (ASCII 13, or ‘\r’) and a newline character (ASCII 10, or ‘\n’). So it basically, sends whatever text you want with a newline termination special character.

Syntax

Everything else is exactly the same as the Serial.print() function that we’ve discussed before.

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Arduino Serial Monitor

The Arduino IDE is equipped with a graphical interface tool called “Serial Monitor” that you can use to communicate with your Arduino board over the serial port (UART). You just need to set the baud rate to the same value you’re using in your Arduino project and you’re good to go. The received text from the Arduino board will show up in the serial monitor and you can also send text messages over UART using this graphical interface.

The Arduino Serial Monitor saves you the time and effort to use external serial terminals on your PC. And it’s really helpful for debugging your Arduino projects by sending the value of variables and flags to check them in real time using the serial monitor.

In the next sections, we’ll do some practical examples to test the Serial.print() and Serial.println() functions using the Arduino Serial Monitor to achieve the following tasks:

• Serial Print a string text message
• Serial Print string text & numeric variables
• Serial Print Float & Double variables
• Serial Print Hex & Binary format variables

So, let’s get started with the Arduino serial print code examples!

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Arduino Serial Print String Example

This is a simple Arduino example code to print the message “ Hello World!!” over the serial port and we’ll view it on the serial monitor.

Code Example

Here is the full code listing for this example.

Code Explanation

setup()

in the setup() function, we’ll initialize the UART module & set its baud rate to 9600 bps using the Serial.begin() function. And we’ll also print the string of text “ Hello World!!” which is the message that we’d like to display only once, that’s why we’re sending it in the setup() function not in the loop() function.

loop()

in the loop() function, nothing needs to be done.

Testing Results

Here is the result of testing this project on my Arduino UNO board. The text message is showing up on the Arduino serial monitor as expected. If you didn’t catch the message, you can restart your Arduino board using the reset button to resend the message again while it’s booting up. Because the message is sent only once during initialization (in the setup function).

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Arduino Serial Print String & Variable Example

In this example, we’ll send a string text message alongside a numeric variable on the same line. We’ll create a counter variable and print its value and keep incrementing it and send the data over UART every 250ms.

Code Example

Here is the full code listing for this example.

Code Explanation

We’ll create a counter variable with an initial value of 0.

setup()

in the setup() function, we’ll initialize the UART module & set its baud rate to 9600 bps using the Serial.begin() function.

loop()

in the loop() function, we’ll print the string of text “ Counter =” which is the message that we’d like to display before the numeric value of the counter variable itself. Then we’ll use the Serial.println() function to print the counter value with a line termination character, increment the counter, insert a small delay, and keep repeating.

Testing Results

Here is the result of testing this project on my Arduino UNO board. The text message + numbers are showing up on the Arduino serial monitor as expected.

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Arduino Serial Print Float & Double Example

In this example, we’ll send a float and double variables with a different number of precision digits (after the decimal point). The floating-point number is chosen to be pi (π).

The float data type has 7 digits of precision, while the double has 15 digits of precision (after the decimal point).

Code Example

Here is the full code listing for this example.

Code Explanation

We’ll create a double variable and a float variable and save into them the pi (π) number.

setup()

in the setup() function, we’ll initialize the UART module & set its baud rate to 9600 bps using the Serial.begin() function. And we’ll send both the float and double variables. The first printed value with the default precision, is followed by other print operations with a specific number of precision digits for each.

Print the float variable with default precision, 3 digits, and 7 digits.

Print the double variable with the default precision, 3 digits, 10 digits, and 15 digits.

loop()

in the loop() function, nothing to be done.

Testing Results

Here is the result of testing this project on my Arduino UNO board. The float & double numbers are showing up on the Arduino serial monitor as expected.

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Arduino Serial Print Hex & Binary Example

In this example project, we’ll print one variable in different formats (Hexadecimal, Decimal, Octal, and Binary).

Code Example

Here is the full code listing for this example.

Code Explanation

First of all, we’ll an integer variable with a random value, let’s say the following.

setup()

in the setup() function, we’ll initialize the UART module & set its baud rate to 9600 bps using the Serial.begin() function. And we’ll send the variable Var to be printed over the serial port in different formats (Hexadecimal, Decimal, Octal, and Binary).

loop()

in the loop() function, nothing to be done.

Testing Results

Here is the result of testing this project on my Arduino UNO board. The number in all formats is showing up on the Arduino serial monitor as expected.

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Wrap Up

To conclude this project tutorial, we can say that using the Arduino Serial Monitor and Serial Print function are crucial for debugging your Arduino projects. We’ll be using them a lot in this series of tutorials and projects. So make sure to try the examples provided in this tutorial to get the hang of it.

If you’re just getting started with Arduino, you need to check out the Arduino Getting Started [Ultimate Guide] here.

And follow this Arduino Series of Tutorials to learn more about Arduino Programming.