Well then we can’t be sure if it goes into bootloader mode. GPIO0 must be low (Home · espressif/esptool Wiki · GitHub).
If these are the schematic of your board, do the following:
- connect the board to the computer
- open a serial monitor (e.g.
miniterm.py) on your serial device at 115200 baud - connect the IO0 pin on the board to GND via a jumper cable
- press the RESET button
- is there any output in the serial monitor window?
It’s kinda suspicious that the pinout diagram next to IO4 simply says “5V” and IO0 simply “GND”. Maybe that’s wrong? The ESP32 I/O pin should not be getting 5V. Maybe double check that with a multimeter. My guess is that there is a pullup on the board that pulls it to 3.3V, so that it doesn’t enter the bootloader. If in doubt, use a pull-down resistor (e.g. 10k or less) instead of a direct jumper connection to GND.