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Arduino Uno not recognised over USB

Contributed by CircuitScope · Added 05 Oct 2026 · 2 views

No COM port? Work through the USB-serial path.

When an Uno doesn't enumerate as a COM/serial port:

  1. Try a different data USB cable and port — many cables are charge-only.
  2. Check the ATmega16U2 (USB-serial bridge, or a CH340 on clones) — a driver or a dead 16U2 is the usual cause.
  3. Install/repair the driver (Arduino IDE bundles them; CH340 needs its own driver).
  4. If the 16U2 is dead you can re-flash its DFU firmware, or program the ATmega328P directly via the ICSP header.