If connecting fails, the app shows the reason and matching tips below the Connect button. What exactly happened shows a report you can copy.
The machine is not in the list
- Browser: only Chrome, Edge and Opera on desktop computers support Web Serial. Firefox, Safari and phones do not.
- Cable: some USB cables only charge and carry no data. Try another cable, directly on the computer instead of a hub.
- Driver (Windows): most hobby machines use a CH340 chip. Without its driver, nothing appears. Get it from the chip maker (WCH: CH341SER) or your machine's maker. The same applies to FTDI and CP210x chips.
- Power: is the controller switched on? Some boards only run with their power supply.
The port is busy
A port can only be used by one program at a time. Close other CNC and laser programs, Arduino tools and terminals. Some CNC programs install a background service that keeps the port busy even without an open window; stop or uninstall it and restart the computer.
No answer
The port opens, but nothing comes back:
- Check the machine's power supply and emergency stop.
- If the machine has a display or offline controller, it must be in USB mode.
- Choose the right port; there can be several “USB Serial”.
- Switch the controller off and on again.
Garbage characters
Unreadable characters mean a wrong baud rate. The app tries the usual values by itself and remembers the right one. You can also set the baud rate under Set up machine; 115200 is common.
Not Grbl
If the device answers but not like Grbl, the app shows the answer. The controller then runs other firmware (such as Marlin) or it is the wrong device. The app speaks Grbl 0.8 to 1.1, grblHAL and FluidNC.
Connection drops
- Route the USB cable away from spindle and motor cables, as short as possible and shielded.
- Turn off USB power saving in Windows.
- Do not close the tab; the app keeps the connection in the background, but not without an open tab.