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USB-to-TTL adapter (CH340 / CP2102) not showing up as a COM port?

1. Driver

Windows 10 / 11 installs drivers for most CH340, CP2102 and FT232 adapters automatically, but some models and older systems need the driver from the chip vendor. In Device Manager, a USB-SERIAL entry with a yellow mark under “Other devices” means the driver is missing.

2. Charge-only cable

Many USB cables carry power only. Try a cable you know transfers data.

3. Power or contact

Try another USB port, preferably directly on the computer rather than through a hub.

QCCOM rescans ports every second and lists the chip and VID:PID (e.g. COM5 · CH340 (1a86:7523)); a newly plugged device is selected automatically, so it is easy to see which port is yours.