Using SIM900A MINI V3.8.2 Module with ESP32

Thread Starter

zazas321

Joined Nov 29, 2015
893
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 :
1616754590575.png

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

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:

20210326_122554.jpg


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

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Yaakov

Joined Jan 27, 2019
3,519
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.
 

Thread Starter

zazas321

Joined Nov 29, 2015
893
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)
zaza 20210326_131915 cropped.jpg

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

However, looking at other similar modules such as :
1616757815057.png

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
 

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Yaakov

Joined Jan 27, 2019
3,519
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.
 
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