Update your Mercury V1

Three things to check, in order:

1. Cable. Many USB cables, especially short ones bundled with phone chargers, carry power only and have no data lines. Try a different cable, ideally one you know works for data transfer.
2. USB port. Some USB hubs are unreliable. Plug directly into the computer if you can.
3. Other software. If the Arduino IDE, PlatformIO, PuTTY, screen, or any serial monitor is currently open, close it. Only one program can hold the serial port at a time.

Web Serial is required and is supported only in desktop Chromium-based browsers — Chrome, Edge, Opera, Brave, and Vivaldi all work. Firefox and Safari do not. Mobile browsers do not either; you must be on a PC or laptop.

If you are on a supported browser and still do not see the Connect button, your browser may be out of date — update it and try again.

This is almost always cable movement. Even small bumps to a USB cable can interrupt the connection mid-write. Make sure the cable is firmly seated at both ends and avoid touching either the cable or the device while the progress bar is running.

If it keeps failing, try a different cable or a different USB port before assuming the device is at fault.

Some computers cut power to USB ports when the screen sleeps, which interrupts the flash. If this happens, just put the device back into boot mode and run the update again — partial writes are recoverable.

For long updates it can help to temporarily disable sleep in your OS power settings.

No. Installing the wrong firmware will not damage your device. Put it back into boot mode and use the Full Install option to start fresh with the correct firmware.