Esp32 UART grounding problem

KimKim
Posts: 1
Joined: Fri Apr 12, 2019 10:47 am

Esp32 UART grounding problem

Postby KimKim » Fri Apr 12, 2019 10:54 am

We have a very strange problem.

We have connected Teensy 3.2 board (3.3V levels) Tx, Rx and GND to ESP32 development board. and made simple communication test SW.

The communication fails, except it work if we disconnect ground and power Esp32 from battery. i.e. only Rx and Tx connected.

How is this possible? and why is it not working when GND is connected?

ESP_houwenxiang
Posts: 118
Joined: Tue Jun 26, 2018 3:09 am

Re: Esp32 UART grounding problem

Postby ESP_houwenxiang » Wed Apr 17, 2019 9:27 am

Hi, KimKim
Has this problem been solved? If not, can you provide a picture showing how you connect the two boards and the battery?

thanks !!
wookooho

cookie
Posts: 1
Joined: Sun Dec 20, 2020 2:52 pm

Re: Esp32 UART grounding problem

Postby cookie » Sun Dec 20, 2020 3:02 pm

Hi ESP_houwenxiang ,

I have the same problem as KimKim. When I'm connecting GND of SIM800L to GND of ESP32, the ESP32 start to not working and it starts be invisible from ArduinoIDE (connecting problems when trying to upload a program (Connecting........_____....._____....._____....._____)). When I'm disconnecting GND it instantly starting work and upload the program.

Also I've tried to test if esp32 itself working when GND is connected - I've put some loop that writes in the Serial Monitor function into esp32 and after connecting GND it stops writing, after disconnecting - start to writing again. So I'm pretty sure that the UART GND breaks something.

I connected the modules exacly like on this picture (excluding other devices)

https://content.instructables.com/ORIG/ ... 111d5be699

Also power supply of SIM800L is 3.7V Li-Poly battery. SIM800L works fine, it indicates by LED that is connecting to the network, so power supply is correct. The only problem is no UART connection between modules without GND between modules.

ESP_Sprite
Posts: 8921
Joined: Thu Nov 26, 2015 4:08 am

Re: Esp32 UART grounding problem

Postby ESP_Sprite » Mon Dec 21, 2020 3:42 am

GPIO2 must be unconnected or low when entering download mode. Your SIM800L is connected to that pin; my guess would be that it pulls the pin high preventing the ESP32 from properly entering download mode.

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