Reading message from GSM modem using PIC16F877A

[niranjan23]

Hello!
I am Interfacing GSM modem to PIC16F877A and receiving message from GSM modem.
I read all previous threads about reading and receiving messages from GSM modem but they were not helpful to me!:-(
also I googled it several nights but didn't find the solution!!!
Since if anyone give me simple C code on receiving message from GSM modem that would be very grateful.:grin:
I'm using Hitech C compiler and SIM800 GSM Modem with PIC16F877A microcontroller!Thanks!!

 

[chandu.kurapati]

Hi,

First try to test commands using terminal for understanding functionality.

Writing simple c code bit a matter, you can find so many SIM800 interface code on google.

 

[niranjan23]

Hi,

First try to test commands using terminal for understanding functionality.

Writing simple c code bit a matter, you can find so many SIM800 interface code on google.

There is little problem with my GSM Modem since I never tested on PC.but when I connect GSM modem to PC on hyperterminal and send AT at first it gives me reply OK..but after that it show" OVER VOLTAGE WARNING" what does that mean??:???: that message continuously displayed on Terminal window.!!!

 

[KlausST]

Hi,

OVER VOLTAGE WARNING" what does that mean??

Isn't it quite obvious?

The message tells that there is overvoltage. Most probably in the supply if the modem.
--> read the datasheet about supply voltage specification.
Then use a DVM and check if the supply voltage is within specification.

Klaus

 

[niranjan23]

Hi,


Isn't it quite obvious?

The message tells that there is overvoltage. Most probably in the supply if the modem.
--> read the datasheet about supply voltage specification.
Then use a DVM and check if the supply voltage is within specification.

Klaus

Ohk I got it.Now I Im using 12V,1A DC adapter for modem,I have two GSM modem and I bought 2nd one 2 days ago..... and it is SIM800 based......Both GSM modem are showing same messages.!!! I vary the power supply from 6V to 12V but still same message."OVER VOLTAGE WARNING".!!!Also I have checked voltage between VBAT and VDD and Its VBAT= 4.37V and VCC =4.94V on DVM
I checked the datasheet of sim800 coz I have sim800 gsm module.It says....
"4.2.2.3. Over-voltage or Under-voltage Power off
The module software monitors the VBAT voltage constantly.
If the voltage ≤ 3.49V, the following URC will be reported:
UNDER-VOLTAGE WARNNING
If the voltage ≥ 4.3V, the following URC will be reported:
OVER-VOLTAGE WARNNING
If the voltage < 3.39V, the following URC will be reported, and the module will be automatically powered off.
UNDER-VOLTAGE POWER DOWN
If the voltage > 4.4V, the following URC will be reported, and the module will be automatically powered off.
OVER-VOLTAGE POWER DOWN"

I dont understand why both the modem are acting like this.????One of them is new!! PLZ HELP ME!!

 

[KlausST]

Hi,

Maybe the modem expects a LiIon battery connected.

Klaus

 

[nandhu015]

Modem should be powered around 4V for proper operation.

As per your post the voltage at 4.94 which is greater than the specified limit, thus the modem switches off on over voltage

 

[niranjan23]

Hi,

Maybe the modem expects a LiIon battery connected.

Klaus

No there is no such a thing like battery holder or connecter!!!

- - - Updated - - -

Modem should be powered around 4V for proper operation.

As per your post the voltage at 4.94 which is greater than the specified limit, thus the modem switches off on over voltage

I tried 5V but modem is not responding!!and there is LM317 on mobem!!

 

[KlausST]

Hi,

You say "VBAT"....this usually is short for "battery voltage".

Klaus

- - - Updated - - -

Hi,

I just opened the datasheet. It clearly says:
***The single 3.7V Li-ion cell battery can be connected to SIM800 VBAT pins directly.****
--> please read the datasheet yourself.

***The power supply range of SIM800 is from 3.4V to 4.4V. Recommended voltage is 4.0V. ****
So connecting 12V or even 5V maybe killes (killed) your modem....or parts of it.

That's why there are datasheets.
LM317 on modem or not .... if it says 3.4V ....4.4V then you have to keep on that.
In any other case don't complain if it does not work.

Klaus

 

[paulfjujo]

hello

UNDER-VOLTAGE WARNNING
If the voltage ≥ 4.3V, the following URC will be reported:
OVER-VOLTAGE WARNNING
If the voltage < 3.39V, the following URC will be reported, and the module will be automatically powered off.

maybe a mistake in the datasheet ?
OVER must be >
UNDER must be <
the reverse could be more easy to understand.
and when surge of comsuption of current , voltage decreases !

I am using a GSM QUECKETEL and had many problems, when using without external Battery 3,7V
because when the GSM exchange some data with MCU,
some spike of current appears and with a LM317 , maxi could be 1A max, not enough
maybe needs spike of 2 amps ..
so unexpectead reset of MCU occured.

The power supply of GSM is an important key to solve many problem.
The battery can supply, absorbe all spike of current needed by the GSM.