Serial Port Monitor

How to use the serial monitor

1. Plug in your Arduino, ESP32, Raspberry Pi Pico, GPS module or USB-to-serial adapter (FTDI, CH340, CP210x, PL2303).
2. Under Port settings, choose the Baud rate your device uses. Select Custom… for unusual speeds such as 74880 (the ESP8266 boot log). Leave Data bits, Parity, Stop bits and Flow control at 8, None, 1 and None unless your device’s documentation says otherwise: that is the common “8N1” setting.
3. Press Choose port and connect. The browser opens its own list of serial ports; pick your device and confirm.
4. Incoming data appears in the Terminal. Switch between Text and Hex, turn Timestamps and Autoscroll on or off at any time.
5. Type a command in Line to send, choose the Line ending your firmware expects and press Send (or Enter). Sent lines are shown with a leading >.
6. Press Download log to save what is in the terminal as a text file, Clear to start again, and Disconnect before unplugging or before opening the port in another program.

Serial settings explained

A UART sends each byte as a start bit, 5 to 8 data bits, an optional parity bit and one or two stop bits. Both ends must agree on these settings; a wrong Baud rate is the most common cause of garbage characters such as ⸮⸮⸮ or random symbols. Typical values:

• 9600 and 115200 baud: Arduino sketches (Serial.begin(…)) and most modules;
• 74880: the ESP8266 boot messages, before your sketch changes the speed;
• 4800 or 9600: many GPS receivers (NMEA sentences);
• Hardware (RTS/CTS) flow control: modems and some industrial adapters, when the RTS/CTS wires are connected.

With a native USB board (Arduino Leonardo, Pico, ESP32-S2/S3), the “baud rate” is often ignored because the data travels over USB directly, but it still has to be set.

Text and hex views

The Text view decodes the bytes as UTF-8 and splits them into lines at LF, CR or CR+LF, even when a line ending arrives split across two USB packets. Each line is stamped with the time its first byte arrived, to the millisecond. The Hex view shows every received chunk as a hex dump: offset, 16 bytes per row in hexadecimal and a column with the printable ASCII characters. Use it for binary protocols (Modbus RTU, sensor frames) or to see invisible characters such as 0D 0A (CR LF) or 00.

The terminal shows the latest 1,500 lines, and the tool keeps the last 5,000 lines or chunks in memory. Download log saves them in the current view, with timestamps if they are switched on.

Line endings

Many firmwares only process a command when they receive a line ending. Arduino examples usually read until LF (\n), AT-command modems expect CR (\r), and Windows-style consoles use CR+LF. Choose None to send the exact bytes you typed.