Entering automatic bootloader with esp32_devkitc (without using usb)

[willemmerson]

I am trying to program an esp32_devkitc v4 without using the usb port - we have developed a pcb around an esp32 and I would like to know that I can program the devkitc reliably over serial as proof of concept before I try the pcb.
I connected EN and GPIO0 directly to RTS and DTR pins of a usb-serial adaptor (https://ebay.us/Feqgyp) but it doesn't flash. If I press 'Boot' button it does work which implies EN/RTS is working but GPIO0/DTR part is the problem.
I tried using the transistors circuit as in devkitc (https://dl.espressif.com/dl/schematics/ ... v4-sch.pdf) but it didn't work at all, and the esptool documentation (https://github.com/espressif/esptool/wi ... bootloader) implies this is only needed if NOT using esptool. I am using IDF v3.2.2.

[autodog]

Ignoring flashing for a moment, do you see anything on your USB-Serial adapter? You should see some form of debug output when you power up the device. If not, then you'll want to verify your TX/RX connections aren't swapped, UART is configured to the correct baud rate (e.g. 115200 8-N-1), etc.

When you do try to flash, what kind of error messages are you seeing?

I recently faced all of the same problems for a new custom design without a USB-UART onboard.

-AD

[willemmerson]

Yes I am getting output from the adaptor and I am able to flash when I hold the boot button, implying TX, RX and EN are working as intended.
What I'm unsure about from the esptool docs is whether it's sufficient to connect EN directly to RTS and GPIO0 directly to DTR (assuming esptool is used for flashing) or whether additional circuitry is required. The problem is I don't actually know anything about electronics, this might be obvious to someone who does.

[willemmerson]

Entering automatic bootloader actually works on the custom pcb, so I guess it must have been something on the devkitc interfering.