The Serial Monitor

The Serial Monitor provides a way to send/receive information to/from your Arduino code. You can use it to view debug messages printed by your program, or to send commands that control your program.

Arduino Uno and Mega

Both the Arduino Uno and Mega have hardware support for the Serial protocol (USART). The Serial Monitor will automatically attach to the hardware serial port and detect the baud rate, so it'll work out of the box without any special configuration.

You can use Arduino's Serial class to interact with the Serial monitor:

void setup() {
  Serial.begin(115200); // Any baud rate should work
  Serial.println("Hello Arduino\n");
}

void loop() {
  // Do nothing...
}

warning

The serial monitor will only show once you print some output from your program. To change this behavior, see below.

The Arduino Mega has multiple hardware Serial ports. You can connect the Serial monitor to a different serial port by configuring the pins in diagram.json. For instance, to connect Serial2 to the serial monitor, add the following lines to the connections section in your diagram:

  [ "mega:17", "$serialMonitor:TX", "" ],
  [ "mega:16", "$serialMonitor:RX", "" ],

Replace mega with the actual id of your wokwi-arduino-mega part.
Note that you need to connect $serialMonitor:TX to the RX pin of the serial port, and $serialMonitor:RX to the TX pin of the serial port. This can be confusing, I know.

ATtiny85 + SoftwareSerial

The ATtiny85 chip does not have a built-in hardware support for serial communication (UART). You can use a software implementation of the UART protocol to interact with the Serial monitor, using the "SoftwareSerial" library.

First, define the pins that will be used for Serial communication, by adding the following lines to the connections section of your diagram.json file:

  [ "tiny:PB0", "$serialMonitor:TX", "" ],
  [ "tiny:PB1", "$serialMonitor:RX", "" ],

Replace tiny with the actual id of your wokwi-attiny85 part, and PB1/PB0 with the pin names that you would like to use.

Then, configure the SoftwareSerial library accordingly:

#include <SoftwareSerial.h>

SoftwareSerial Serial(PB0, PB1);

void setup() {
  Serial.begin(9600); // Must be 9600
  Serial.println("Hello Arduino\n");
}

void loop() {
  // Do nothing...
}

Make sure the the pin names in your code match the ones in the diagram file. The first parameter to the SoftwareSerial constructor should match the pin connected to $serialMonitor:TX, and the second parameter should match the pin connected to $serialMonitor:RX.

warning

The baud rate must be set to 9600. This is hard coded in the simulator, and using a different value will get you garbage in the Serial monitor.

For a complete example, check out the ATtiny85 SoftwareSerial example project.

Note: if you just want to use the Serial monitor for printing debug messages, take a look at the TinyDebug library.

Configuring the Serial Monitor

You can configure the Serial Monitor by adding a "serialMonitor" section to your diagram.json file.

The default configuration is as follows:

"serialMonitor": {
  "display": "auto",
  "newline": "lf",
  "convertEol": false
}

When you add a "serialMonitor" section, either add it after the last item in diagram.json, or make sure to add a comma after the closing curly brace. You can find a complete example here.

Display

The display property configures when/how to display the serial monitor. The possible values are:

Value	Description
auto	Display the Serial Monitor when there's some output (the default)
always	Always display the Serial Monitor when simulation starts
never	Never display the Serial Monitor
plotter	Display the Serial Plotter when simulation starts
terminal	Display a terminal (using XTerm.js)

Note: the "terminal" mode supports text and background colors. You can check out the Arduino ANSI colors example to see it in action.

Newline

When you input a line of text in the Serial Monitor, the simulator sends that text to your program. Your program can read it using Serial.read() and also some other Serial methods.

By default, the simulator also appends a line feed character ("\n", ASCII code 10) to every line of text that it sends to your program. You can use the newline property to change this behavior and configure a different sequence of characters:

Value	Characters	ASCII codes	Description
lf	"\n"	10	Line feed (the default)
cr	"\r"	13	Carriage return
crlf	"\r\n"	10 13	Carraige return + linefeed
none	""		Don't append any characters to input lines

Convert EOL

The convertEol property only applies to the "terminal" display mode. When set to true, the simulator will convert all line feed characters ("\n") to carriage return + line feed ("\r\n") before sending them to the terminal. This is useful when your code does not print a carriage return character after each line, and the serial terminal displays the output in a staggered way.