These pins are connected to the corresponding pins of the CH340 USB-to-TTL.

Note: users report that the driver for Mac on both old and new computers may be unstable, read this extra link to get it working. In addition, no drivers need to be installed for MacOS Mojave, these are already present. Used to receive (RX) and transmit (TX) TTL serial data. Note 2:The voltage of the TX pin is 5V and is therefore only suitable for communication with 5V systems/chips! Use a level shifter or make yourself a resistance divider to go from eg 5V to 3.3V. Pay attention to the pins if you want to program a Pro Mini with this module! USB to serial chip CH340 English DataSheet Version: 1D 1. Note 1:The pinout is not the same as on our FT232 module which is handy for programming the Pro Mini.

Built-in polyfuse (self-resetting fuse) of 500mA for the 5V via USB.

Features a Reset pin for convenient programming with the Pro Mini.

Converts TTL logic levels to computer RS232 levels.

I used a MOS-FET instead of a transistor for the write circuit, but I was able to confirm that the reset signal and Boot mode signal were output correctly and that the ESP32 entered the write mode.A simple USB to serial converter. The CH340/CH341 USB to the serial port is a 2-wire USB to RS-485 serial communication adap.

The Arduino IDE also allows me to choose the serial port for the circuit I have created. We will be installing a USB to rs485 installation on our computer. When I used CH340K, it was not recognized at all, but this time it is recognized easily.

Let's replace it with the ESP32-DevKitC writer circuit. Shortly after, the circuit was completed. In serial interface mode, CH340 supplies common MODEM liaison signal, used to enlarge asynchronous serial interface of computer or upgrade the common serial device to USB bus directly. I feel that adding 1uF of C2 will prevent the error of not entering write mode when writing the program. CH340 is a USB bus convert chip and it can realize USB convert to serial interface, USB convert to IrDA infrared or USB convert to printer interface. It is a very simple circuit with one IC, two MOS-FETs, and two capacitors. The circuit is almost the same as the other day, using CH340C for the USB serial conversion IC, and MOS-FETs instead of transistors.

Ch340 usb to serial schematic