# Arduino Serial Communication

> Learn how Arduino serial communication works: initialize Serial with a baud rate, then use Serial.print() to send data to your computer and debug projects.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2021-03-31 | Topics: [Arduino](https://flaviocopes.com/tags/electronics/) | Canonical: https://flaviocopes.com/arduino-serial-communication/

To communicate between Arduino and other devices we can use serial communication. This is often used to "talk" to a computer, to visualize data coming from the Arduino, and to debug your projects. Or to communicate with other devices, too.

Arduino comes with the built-in `Serial` library. You don't need to import anything special to use it.

The USB connection we make between the computer and the Arduino to upload the program to the device is automatically set up to handle serial communication, so we can send and receive messages through the Arduino IDE.

Let's now see how to send data through the serial.

In the `setup()` function of an Arduino program you need to initialize the serial communication by setting the the data rate, expressed in bauds, for serial data transmission. Typically `9600`:

```c
Serial.begin(9600);
```

> bauds = bits per second

Then you can use one of the several `Serial` functions.

For example `Serial.print()`:

```c
Serial.print("Hello!");
```

Let's try it by compiling and uploading this program to the Arduino:

```c
void setup() {
    Serial.begin(9600);
    Serial.print("Hello!");
}

void loop() {
}
```

Save and upload the program to the Arduino, then click the top-right button "Serial Monitor" in the Arduino IDE:

![Arduino IDE interface with Serial Monitor button highlighted in the top-right toolbar](https://flaviocopes.com/images/arduino-serial-communication/Screen_Shot_2020-12-11_at_18.19.16.png)

The button will open the serial interface monitor on the computer. Make sure it's tuned to the baud rate set in the program, and you should see the "Hello!" string being printed:

![Serial Monitor window displaying Hello! message from Arduino with 9600 baud rate setting](https://flaviocopes.com/images/arduino-serial-communication/Screen_Shot_2020-12-11_at_18.20.38.png)

`Serial.print()` is just one of the functions you can run.

You also have `Serial.println()` that writes something and adds a `\n` line terminator, so every message is printed on its own line.

You can also send messages to the Arduino from this serial interface monitor. See the input box with the `Send` button on top?

In the Arduino program you can use `Serial.read()`. Characters are encoded using ASCII, and if you run this program:

```c
void setup() {
    Serial.begin(9600);
}

void loop() {
  if (Serial.available() > 0) {
    Serial.print(Serial.read());
  }
}
```

You will see in the serial interface printed back the ASCII decimal value of the characters you send. Try writing `test` and hit `Send`:

![Serial Monitor showing ASCII decimal values 116101115116110 printed on single line after sending test](https://flaviocopes.com/images/arduino-serial-communication/Screen_Shot_2020-12-11_at_19.26.13.png)

It's best to use `Serial.println()` to have each number printed on a single line:

![Serial Monitor with timestamped ASCII values 116, 101, 115, 116, 10 displayed on separate lines using println](https://flaviocopes.com/images/arduino-serial-communication/Screen_Shot_2020-12-11_at_19.23.21.png)

`116` is the ASCII encoding for `t`
`101` is the ASCII encoding for `e`
`115` is the ASCII encoding for `s`

And `10` is the new line character.

> See my list of [printable](https://flaviocopes.com/printable-ascii-characters/) and [non-printable](https://flaviocopes.com/non-printable-ascii-characters/) ASCII codes.

To print the character instead of the ASCII encoding, use the `Serial.write()` function:

```c
void setup() {
    Serial.begin(9600);
}

void loop() {
  if (Serial.available() > 0) {
    Serial.write(Serial.read());
  }
}
```

![Serial Monitor displaying test echoed back as characters using Serial.write function](https://flaviocopes.com/images/arduino-serial-communication/Screen_Shot_2020-12-11_at_19.24.51.png)

`Serial.available()` makes sure there's data ready to be read. It returns `-1` if no data is sent, so if we don't add this check we'll just see a bunch of `-1` repeated in the serial monitor.

There are more functions you can use in the Serial object.

Check them all in details here: <https://www.arduino.cc/reference/en/language/functions/communication/serial/>.

It's important to note that on the Arduino you have a `tx` and a `rx` set of pins. On the Arduino Uno they are pins 0 and 1, on a MKR 1010 they are pins 13 and 14. Do not use those pins for I/O when you use serial communication via USB, or you might have interferences in your data.

That said, those pins are used as the serial interface, which is very useful to communicate directly to other devices, and not with your computer through USB.