SIM900 won't receive sms

Using Arduino Networking, Protocols, and Devices
1

Hi all,

I'm new in here and I have big problems with my GPRS shield. It's made by Greetech, based on SIM900. I need it for sending and receiving SMS messages. It'll send messages without any problem but I can't get it to receive any messages.

I have tried for many different ways, but always the same thing. It'll give me a notice, that there is a message "REC UNREAD" but it won't show me the real message. And next time after a restart, if I try to read it, it'll say that "REC READ", but again it won't show the message. I can see the number, where it has been sended, date, part of the time and that's it. If I try to reread the message without restarting the shield, it will mix up the whole thing. Pictures below will show how SSCOM is showing this.

First try

Second try

What I'm doing wrong? Or is the problem the shield it self?

2

I think you modem is in PDU Mode when you reboot it.
Try to set it to TextMode using at+cmgf=1 before trying to read the message.

3

Thanks for fast reply. I tried that and after giving a command at+cmgf=1 it says OK, but it didn't make any difference. It's still acting same way than before.

4

What SMS did you send to the modem?
Just ascii right?

5

Yes just ascii. I'm living in Finland, but I used just regular ascii, not Scandinavian ones.

6

Ok, problem solved. The serial connection buffer was too small, causing memory overflow. I increased it to 64 and it started to work.

But anyway thanks HugoPT for you're time.