Failed to connect to ESP32 in bootloader mode

[langestefan@msn.com]

Hi,

I have two ESP32 devkit boards:

1. NodeMCU ESP32-S devkit board (from ebay)
2. ESP32_devkitc_V4

I can program both using the onboard FTDI/USB. It goes into bootloader mode and esptool is able to program it fine.

Now I need to be able to program the devkitc with an external FTDI, since I have a custom PCB that has the same ESP32 module on it but no onboard FTDI. This is where I run into a problem.

The devkitc board goes in to bootloader mode succesfully using the EN and BOOT onboard buttons:

Code: Select all

[2019-03-17_15:39:50]rst:0x1 (POWERON_RESET),boot:0x3 (DOWNLOAD_BOOT(UART0/UART1/SDIO_REI_REO_V2))
[2019-03-17_15:39:50]waiting for download

But when I try to use esptool to program it, I receive this error:

Code: Select all

Serial port COM3
Connecting........_____....._____....._____....._____....._____....._____....._____

A fatal error occurred: Failed to connect to ESP32: Timed out waiting for packet header
*** [upload] Error 2

I have:

Code: Select all

TX --> RX
RX --> TX
3v3, GND.
Using onboard EN/GPIO0 buttons

Programming using an external ftdi works fine using the cheap ebay ESP32 NODEMCU board! (using the exact same setup)
How is this possible?
Are there differences affecting the bootloader process between different ESP32-WROOM packages?

I have already spent several hours debugging this so I would really appreciate it if someone could help me!

I have added pictures of the boards I'm using.

Greetings, Stefan

[ESP_Stone]

I guess there would be some timing issue about EN and GPIO0. Suggest you can use oscilloscope to measure EN and GPIO to make sure GPIO0 keeps low when EN goes high at boot mode.Thanks.