The CH340 is a popular converter module that provides TTL serial communication over the USB port. It is standard in Arduino clones because it is much more common and cheaper than the CP2102. The voltage selection jumper on the module allows switching between 3.3V and 5V logic levels, making it possible to use the same module in ESP-01 (3.3V) and classic Arduino (5V) projects. TXD, RXD, GND, VCC pins are used for programming ESP-01, ESP32-CAM and other boards without USB ports.
