[Moved] SIM 908 not responding to AT

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uhuzaifa

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Hi there,

I am working on Sim 908 GSM+GPS module. I wanted to see if it works perfectly with the PC so I connected the module with the PC and ran Realterm (a terminal software). After a lot of tries of entering at\r I finally got the 'OK' response and then I successfully sent a few SMS to a few numbers too.

Now I am trying to connect and get at least an 'OK' response but all in vain. However, as I reset the module, I receive the following sequence: 49 49 49 49 on the terminal screen and that is all I get no matter what I type after this.

Kindly guide me how can I trouble shoot?
 

Re: SIM 908 not responding to AT

it sounds like you have the incorrect baud rate but you had it working at one point
what happened between it working and not working?
could you have changed the modem baud rate or switched on autobauding?
have you tried switching the modem off and on to reset it?
 
Last edited:

Re: SIM 908 not responding to AT

Thank you
Once again it started working on a different terminal software, docklight. But after a few hours, same problems appeared again.
yes i tried without changing the baud rate.
at one point it started giving this error that:
"COM port x could not be opened" although everything was connected
 

Re: SIM 908 not responding to AT

very strange - could the modem be going into power down mode?
what happens if you switch off/on the power?

I tend to use tera term pro as a terminal emulator
http://ttssh2.sourceforge.jp/

usually if I get "COM port X unable to open" another program has it open (sometime I have to use the Task Manager to kill the program)
 

Re: SIM 908 not responding to AT

Let me check that
But if I keep the modem off for some time like 3 or 4 hours I can use it again without a problem like now I have again got it working
But how can I check the power down condition ?
I didn't send any such commands for that
 

[Moved] Arduino serial communication with sim 908

Hi there,
I am working on sim 908 and I am trying to serially communicate with it using arduino mega 2560 . But the problem is, when I send "AT\r" serially I should be getting in response, following:
AT\r
OK\r\n
But I get a lot of garbage
I am using 9600 baud rate 8 data buts 1 stop bit and no parity
Any ideas??
 

Re: [Moved] Arduino serial communication with sim 908

try a few other baud rates, e.g. 19200, 38400, 56700,115200
the Sierra AirPrime HL6528x modems I am using at the moment default to 115200baud

- - - Updated - - -

uhuzaifa said:
Let me check that
But if I keep the modem off for some time like 3 or 4 hours I can use it again without a problem like now I have again got it working
But how can I check the power down condition ?
I didn't send any such commands for that
Click to expand...
sounds as though you may have a faulty modem - is it overheating? or the power supply failing - check the voltage?
get onto your supplier or the the manufacturers?
 

OK its working for the moment and now i have another problem.
I have interfaced the DB-9 port of the GSM module with the RX2, TX2 pins of the Arduino Mega 2560.
I have written a code that sends 'AT\r' continuously and observes the response from the GSM module.
Desired Response should be:
AT\r
OK\r\n
But i get 'AT\r' and after that i get a lot of garbage values
Sometimes even i dont get this response in consecutive form. Like i get
'A<garbage>T<garbage>\r'

Kindly suggest some troubleshooting technique.
 

have a delay of several seconds between transmitting each "AT\r" - you may be sending it commands too fast to process the response

is the Arduino UART receiver code receiving charcaters from the modem interrupt diven?
if not you may be receiving characters from the modem faster than you are empting the UART Rx buffer causing overrun and getting garbage
 

Hi guys,
I think I have resolved most of the problems i was facing. Now i can send the sms easily through the arduino but there is a hitch in this.
I have to connect the serial cable to the computer for this communication. That is, for successful communication between Arduino and SIM 908, I have to keep the module connected to the computer. Does this make sense? How can I solve this problem?
 

Hi! What does you meaning?
Didn't you connect the SIM module to Arduino PCB ?
Didn't you operate SIM module through Arduino UART ?
As the above mentioned,you connected the module to a PC with a UART DB9 wire,did it work fine? Which lines are you using with DB9? Tx,Rx,GND ,only these three lines ? or some other lines? e.g. CTS,RTS,with hardware flow control ?
 

<Q>Didn't you connect the SIM module to Arduino PCB ?
Didn't you operate SIM module through Arduino UART ?

Yes I have connected my SIM module with ARduino UART and I am sending AT commands from Arduino
But I have also connected the SIM module with PC using DB9 connector (But I am not sending anything from PC to the module.) I have connected the wire to the DB 9 connector and whatever lines there are already (I didnt select any specific lines to be connected or disconnected from the DB 9)
 

We can only guess about the exact circuit. There will be a level converter (e.g. MAX232) between DB9 RS232 level signals and SIM908 TTL level. Arduino uses TTL level and must connect directly to SIM 908. This means that the level converter must be disconnected before, otherwise you get conflicting signals at the SIM908 RXD, DTR and RTS inputs.
 

OK i get it.

I have another problem.
I am almost done with the project and now i am test running everything in the integrated form. I was trying the GPS for getting the location co ordinates. My Debug Serial Port is giving me co ordinates too but when i try
AT+CGPSINF=2 for getting GPS co ordinates, I only get 0 N and 0 E and the data format shows that no satellite has been found. At that time, Debug port also gives 0 0 but then after a few seconds, Debug Ports starts giving the correct co ordinates again.

Any ideas please.
 

u r getting 0n,0e bcoz ur modem is not hvg a clear view of the sky.....if it gets dem within 30 sec max it starts gvg the correct rersponse......
 

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