MOD-GSM SIM problem [SOLVED]

[Fayev]

Hi everyone,

I'm trying to use a MOD-GSM for a project with SMS but it won't get the GSM network signal. I've placed the SIM card without PIN on the card holder, I've powered the module with 12V (BAT_E jumper open) and then turned it on pressing the wake up button for around 2 secs. Then I all the SIM number to check the network and it never rings,it appears as if it wa off all the time. What can be the error here?

Thank you all for your time!

[dave-at-axon]

Does it respond to AT commands?

You can send an AT+CREG? to get back the status of registration.

[Fayev]

Thank you for your answer! It was working fine with another SIM card and a list of AT commands, but now it won't recognize this new SIM. I understand this is how is supposed to work:

- Insert an unlocked SIM
- Press wake up button for about 2 secs.
- See the status LED blink twice
- See the status LED blink On and Off like this: 100100100...
- And that means that the SIM is now working

But in this case, it blinks but there's no signal when I call to the SIM.

[dave-at-axon]

Can you do AT commands to it?

Regardless of the fact it has a SIM or not, AT commands should always work. How else can you do an AT command to check for the SIM.

Have you tried powering up without the SIM? AT command should still work. You might have a faulty SIM that's preventing it from starting.

[Fayev]

Thank you for your replies dave-at-axon, the board is fine, the SIM was the problem, the board does receive AT commands, when I changed for a SIM card from a different provider it worked fine..

Until now, that the MOD-GSM is answering with some trashy ASCII and I can't find the problem, I've already tried different baud rates (300,9600,115200) none of them giving good results..

My board is the Rev. A, so this part from the manual would apply, right?:

The information below is for older revisions of the board. If your board doesn't
have the serial resistors mentioned below then there is no need to perform the
actions mentioned below!
If MOD-GSM doesn't transmit properly data on the UEXT of another Olimex board,
it might be because some other boards can interfere with MOD-GSM's signals. If the
host board has any signal on the I2C and/or the SPI on the UEXT there is very high
chance of erroneous behavior.
There are two workarounds:
1. Cut the UEXT cable wires 5,6,7,8,9,10. Only wires 1,2,3,4 (NC, GND, RXD, TXD)
should remain.
OR
2. Remove resistors R19, R20, R21, R23, R24, R25

I've done the 1st, just using those pins from the UEXT, but noise gets in anyway.. Resistors from option 2 are too small and I'm afraid I'll damage the board if I try to remove them... Is there anything else I can try?

Thank you in advance!

[LubOlimex]

Hey there Fayev,

The baud rate it is set on hardware level to 115200. Consider using 115200 when connected to the terminal or host board.

You can test just the UEXT port of your computer by connecting RX and TX line of the cable. Then if everything is alright you should receive echo on the computer. If the computer is ok, then inspect the settings of the terminal program (parity, etc - should be default).

Best regards,
Lub/OLIMEX