The loopback test is a troubleshooting procedure to test the serial communication between an Arduino board and your PC. A failed loopback test indicates a problem with one or more of the following:
- The host computer
- Hardware driver
- USB cable
- The board's USB to Serial converter
Disconnect the board from your computer or battery.
Remove all shields, jumper cables, and other connections from the board.
Connect a jumper cable from RESET to GND.
Connect a jumper cable from Digital 0 (RX) to Digital 1 (TX).
Connect the board to your computer and open the Arduino IDE or the Arduino Create Web Editor.
Ensure that the correct port is selected.
- Arduino IDE: Tools > Port > [Your Arduino Board]
- Web Editor: Select your board using the boards dropdown.
Open the Serial Monitor.
- Arduino IDE: Tools > Serial Monitor
- Web Editor: Select Monitor in the sidebar.
Enter a message and click Send (the baud rate does not matter). Your message should immediately be echoed by the board, and appear in the output field below.
Performing a loopback test in the Arduino IDE serial monitor.