ESP32_Relay_X4_Modbus_v1.3 board with micropython

[triszterer]

Hello,
I bought this board: https://devices.esphome.io/devices/esp32_relay_x4_modbus_v1.3/ and successfully uploaded ESP32_GENERIC-20251209-v1.27.0.bin firmware. After uploading I am not able to connect with mpremote. It returns with error: "could not enter raw repl". My symptom is very similar which I read in topic: https://github.com/orgs/micropython/discussions/15961 but the suggested solution did not help me. Did anybody meet with this problem? Does anybody have any idea or suggestion how to solve this issue?
Thank you in advance,
Tamás

[robert-hh]

Which serial ports do you see on your computer? mpremote uses by default the first serial port, which may not be the one of your board.

[triszterer]

Here is the manufacture's documentation. Not too much but more than nothing.
http://www.chinalctech.com/cpzx/Programmer/Relay_Module/898.html

[robert-hh]

Yes. Just type mpremote command on linux terminal.

Is there any other USB serial device connected? See ls /dev/tty*.

[triszterer]

No. But the problem should not be around this. I have another ESP32 (KC868-A6) with micropython and there is no any issue with it.

[robert-hh]

Did you try the various flash modes? That is a typical problem with ESP8266 devices, and I cannot recall much discussion about this, but it may be worth to try. https://docs.espressif.com/projects/esptool/en/release-v4/esp32/esptool/flash-modes.html

[triszterer]

I tied all. Nothing changed.

[robert-hh]

Looking at the board, I noticed that the espressif two transistor logic for Reset and GPIO seems missing. In that case, the usual settig for RTS and DTR will keep the ESP32 in bootloader mode. You can verifay that by:

1. Reinstall the ESP32 firmware with the default flash mode.
2. Install at the PC picocom with sudo apt install picocom
3. Run picocom -b 115200 --noreset --lower-rts --lower-dtr /dev/ttyUSB0

That should bring up a REPL prompt.

[triszterer]

340XF27 if I read well...

[robert-hh]

picocom is good for REPL, but uploading files is not easy with picocom. One way wold be to change mpremote into not setting RTS and DTR. The place to change is in mremote/transport_serial.py. If I read the code right, the port is opened at line 90. Thereafter, set self.serial.dtr = False and self.serial.rts = False. I have to check if that causes the right level of RTS and DTR.

[triszterer]

Dear Robert,
Thank you all your help in finding out why my ESP32 board does not work that way it is expected. Well, we could move forward one step but there is still no acceptable good solution. Well, I will not be available for 1 week. When I come back I would like to continue this investigation....

[triszterer]

Hello Robert,
I am back....

So, using picocom after powering the device on USB:

So, it is in boot mode for some reason.

Pressing small reset button on the board:

It enters REPL mode. So, I am able to execute some pyton commands.

Though, if I power the device and then press reset button, I am still not able to use mpremote ("could not enter raw repl")

[robert-hh]

Mpremote raises both rts and dtr, keeping the board in reset mode. Ande there is mo option in mpremote to control these signals. Unless mpremote is adapted, it hardly can be used with your board.

[triszterer]

Thank you all your help. I guess I have to buy another ESP32 board.

[robert-hh]

You could try to pull up webrepl. Start a REPL using picocom and connect to WiFi following the instructions at https://docs.micropython.org/en/latest/esp32/quickref.html#wlan. Once Wifi is connected, call

import webrepl
webrepl.start(password="xyz")

You will need the Webrepl APP for the PC. The source and README are here: https://github.com/micropython/webrepl. With webrepl you can get a REPL prompt and move files using your browser.