As you can see in the figure above, the Serial Monitor displays an input field at the top, consisting of a single row and a Send button, and an output window below it, where data from the Arduino is displayed. When the Auto-scroll box is checked, the most recent output is displayed, and once the screen is full, older data rolls off the screen as newer output is received. If you uncheck Auto-scroll, you can manually examine the data using a vertical scroll bar.

​

Starting the Serial Monitor

Before we can use the Serial Monitor, we need to activate it by adding the Serial.begin() function to our sketch in void setup():

​

Serial.begin(9600);

​

The value 9600 is the speed at which the data will travel between the computer and the Arduino, also known as baud rate. This value must match the speed setting at the bottom right of the Serial Monitor, as shown in Figure above.

Sending Text to the Serial Monitor

To send text to the Serial Monitor to be displayed in the output window, you can use Serial.print. (the Serial.print function prints data as a human-understandable ASCII text). 

​

Serial.print("Arduino for Everyone!");

​

This sends the text between the quotation marks to the Serial Monitor’s output window. You can also use Serial.println() to display text and then force any following text to start on the next line:

​

Serial.println("Arduino for Everyone!");

Displaying the Contents of Variables

You can also display the contents of variables on the Serial Monitor. For example, this would display the contents of the variable results:

​

Serial.println(results);

​

If the variable is a float, the display will default to two decimal places. You can specify the number of decimal places used as a number between 0 and 6 by entering a second parameter after the variable name. For example, to display the float variable results to four decimal places, you would enter the following:

​

Serial.print(results, 4);

​

Debugging with the Serial Monitor

The Serial Monitor can be useful in debugging (locate and fix errors) in your sketch. For example, if you insert Serial.println() statements in your sketch containing brief notes about the location in the sketch, then you can see when the Arduino passes each statement.