Issue with Incorrect Voltage Reading from GSM

Projects Networking, Protocols, and Devices
1

I'm encountering an issue with the voltage reading from the VBAT_ADC pin on my GSM module, which is connected to two batteries in parallel. The voltage reading I get is 6499mV, which doesn't reflect the actual battery voltage (around 3.7V). When I use the AT+CBC command, I get the same incorrect reading.

GSM module: A7672S
Controller: ESP32

Is there a known issue with how the GSM module's VBAT_ADC pin handles voltage readings? Could this be related to how the GSM module scales the voltage, or are there settings (such as reference voltage or ADC resolution) that I should adjust?

Any guidance on troubleshooting this or possible solutions would be very helpful!

2

NEVER put batteries in parallel!

3

please explain the reason

4

It is absolutly unsafe!

One battery can discharge into the other with a high current causing it to overheat, and possibly explode.

1 Like
5

Thank you @jim-p for your help. I noted but can't I measure the voltage?

6

There are hundreds of GSM modules. So now we need the datasheet for the GSM module that you actually have.

7

Here is the datasheet A7672S.

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Sorry, I should have said the GSM board you are using.

9

yes, I am using this Simcom A7672S.

10

Are you using something like this?

image
image640×640 86.9 KB

11

I am using this kind (image) of board with same GSM module

12

Thank you.
I will study the datasheets/manuals

13

In the hardware design document it says this
"Voltage monitor function under debugging"

Not sure if they are trying to tell you that it does not work.

14

Also I don't see a VBAT_ADC pin on the board

15

Here the connection :

Screenshot 2025-01-21 160516
Screenshot 2025-01-21 160516752×338 23.4 KB

16

Where did you get that schematic?
It was not in any of the board documents you provided in the links.

17

VADC pin is ADC pin

19

According to the documentation there is no VBAT_ADC pin.
However pin 51 is ADC2.
So try AT+CADC2 to read ADC2

Whatever documantation you have it probably has other errors.

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