Hello. I plan to use this module with my ESP32. I have received this module and I am slightly confused regarding selecting the right jumper combination for my needs:
The module used:

https://www.ebay.com/itm/MINI-V3-8-...on-Module-GSM-GPRS-SIM900A-Good-/281743836908

I have also found some simmilar guides such as :


I am mainly concerned about the jumpers marked in red circle:


However, on my board, the names of the headers are slightly different also, I am not sure what are they used for. Are they for switching between 5V and 3.3V logic?



Following is the picture of my module headers:




In my case, ESP32 is 3.3V logic. Do I need to connect these jumpers in any way ? Thanks in advance

 

The 3VR and 3VT seem to be 3V receive and transmit pins, respectively, no jumpers.

It seems to be a revision providing with 3.3 and 5V at the same time.

 

Hm. Okay. So I want to connect these 3VR and 3VT to my ESP32 rx tx?

At first, I thought that serial RX and TX on the sim module will be located here: (See top of the picture for 3 pin header)


It says OBS-2 and GND. I cannot figure out what is OBS-2.

However, looking at other similar modules such as :


You can see that they say that the 3 pin header as shown in my previous image have TX/RX and GND. And also they say something about those jumpers, apparently, they need to be connected in this strange manner

Moderators note : cropped image

 

Hm. Okay. So I want to connect these 3VR and 3VT to my ESP32 rx tx?

At first, I thought that serial RX and TX on the sim module will be located here: (See top of the picture for 3 pin header)


You can see that they say that the 3 pin header as shown in my previous image have TX/RX and GND. And also they say something about those jumpers, apparently, they need to be connected in this strange manner

From everything I can find, I am convinced that you need to connect the MCU to the 3VR/T pins.