mcu_nerdWhen I was about to program a board with an ESP8266 on it, I needed a USB to serial adapter. I reached for my cheap CH340 based one. I set the voltage to 3.3V, but I decided to check the RX/TX pins with my multimeter before connecting it. I found the voltage on the TX/RX pins to be around 5V. Yup, the voltage switch only changed the voltage on the VCC pin. I checked by FTDI232 based board and set the jumper to 3.3V, and the TX/RX pins read around 3.3V.
Top: CH340
Bottom: FTDI232
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