ESP32 Forum

Hello,

I've got a brand new ESP32 Wrover IB that's soldered on a breakout board that has a 3.3V regulator and some capacitors.

I use a USB-Adapter to connect it to the PC. When opening the serial monitor of the Arduino IDE I repeatedly (~ every 400ms) get this message:
I've used different power supplies like the built-in supply of the USB-Adapter, the on-board regulator and a bench supply. I've checked each setup with the oscilloscope for glichtes but everything looks fine.

Needless to say that I cannot program the module with the Arduino-IDE. When trying I get this:

Error: A fatal error occurred: Failed to connect to ESP32: Invalid head of packet (0x65)


What I've already tried is the esptool with a simple command The result is an error message:

A fatal error occurred: Faild to connect to the Espressive device: Invalid head of packet (0x65): Possible serial nose or corruption.

However, the serial signal on the scope looks clean, there's no noise. Also I've tried this command with lower baud rates which gives the same error.

Now my question is what this error means and most of all how to get rid of it so I can program the device.
I hope there's someone here who is familiar with this sort of problem and can give me some help.
Thank you very much!

Cheers
Markus

Some posts in this forum say that GPIO12 (MTDI) must be pulled up.

The schematic of my breakout board shows that this pin is left floating. When measuring it the voltage is 0V.

The pdf datasheet of this module (https://www.espressif.com/sites/default ... eet_en.pdf) says (page 11):

Internal pull-up resistor (R9) for MTDI is not populated in the module, as the flash and SRAM in ESP32-WROVER-B
and ESP32-WROVER-IB only support a power voltage of 3.3 V (output by VDD_SDIO).


This would mean that everything is fine with GPIO12 and the flash voltage is correct.

Hello, the behavior you described is normal for a newly bought module. I can't say for sure but I believe it is working fine. As for pin statuses, there are 6 pins you definitely shouldn't connect and these are GPIO 6 to 11, I suggest connecting EN pin to a button with pull-up for reset function. Lastly and importantly; IO0 pin, do not use this pin as IO because if this pin is low on boot then ESP enters to FLASH mode. I also recommend to pull-up this pin and connect to a button.

So if you press to reset button while holding flash button then your module will enter to programming mode and will wait for uart/spi programming connection.

There are also some other pin situations like some pins can only be input or some shouldn't be low/high at boot but these 8 pins I mentioned are enough for most basic setup to run ESP.

Good morning,

Thank you very much for this eloborate reply but most of all for this helpful analysis!

I've added a push-button for I0 and pressed it. And voila, the module enters programming mode. A reset button was not needed probably because the module kept resetting itself. However, I will add a reset button as well.

Now I finally can program the module and start with my project!

Thanks again!

Cheers
Markus

Hello again,

If I may, I'd like to ask one more question for clarification.

According to the most helpful reply from elcrcp there are some pins that should not be connected which are GPIO 6 - 11. A push-button with a pull-up resistor is recommended for the enable and the IO0 pin.

The datasheet for this module (https://www.espressif.com/sites/default ... eet_en.pdf) says that the strapping pins are GPIO 0, 2, 5 (identical to IO 0, 2, 5) and MTDI (IO 12) and MTDO (IO15). Obviously these pins should not be used by the application.

GPIO6 - GPIO11 also are labled SCK, SDO, SDI, SHD, SWP, SCS - and now I've found the note on page 10 - these pins are used for the module's integrated SPI-flash.

This already answers my question and it is clear now which pins should not be used.

Cheers
Markus

It is not that those strapping pins should not be used by the application, but rather that they need to be in a known state at boot. If they are connected to devices that you can guarantee that state (outputs or passives with a pull down/up resistor), then go ahead and use them. If they are connected to something that you cannot control the state (ie another active device or bus), then you are much better off using a pin that is not involved in the boot sequence.

Hi.
I have other problem.
I had working ESP32-WROVER with connected temperature sensor. Then I decide to connect another one sensor - DHT21.
And in one big mistake I connect + of sensor to GND on plate and GND of sensor to 3V3. When I see my mistake, I disconnect all sensors.
And now when I connect plate to USB - my computer doesn't see it on any port, and it's doesn't send any data to MQTT.
Is there is any way to fix it or it's complitly dead?

I think I burned this chip. It`s marked S2TI.
Can I replace it? What kind of chip is this?
Thanks