Problem with AT commands on SIM900

[Guculuma]

Hey,

I recently purchased the SIM900 with the Evaluation kit. So I put the whole thing together now and decided to try sending the device AT commands. So I decided to use the arduino IDE serial monitor to send the device commands.

My problem now is that I get a response from the device but it is the exact same result as I was sending to the device:

For example. I sent AT, the response for the Device is AT. Before I send AT and try send 1 or 2 or any character that is not in the AT command set, the device wont respond.
When I restart the device I get funky unreadable characters like y'y'
Also when I push the PWRKEY I get the right message that the device is powering down. not to sure what the message is anymore. And then when I push the button again it gives me those funky letters again.

Also, When I start the device up I switch the pwr switch on then the download switch on and off so the status light turns on.

I was playing around with the baud rates and with some baud rates the device return funky characters and with the specific baud rate the device is set to in the device manager it returns the same command that I sent the device.

I donno if im doing something wrong or if its a problem with the device. I dont know what to do anymore. Is there anything im missing? Any help would be greatly appreciated. Thanx

 

[FvM]

The first point is to understand about the autobaud feature of a Hayes-compatible modem. The second is to read the product manual thoroughly.

For the first point, when in default autobaud mode, the modem detects the peer's speed when receiving the character sequence A T. To work for autobaud, the characters must be preceeded, separated and succeeded by some delay, just the same as when you type it at Hyperterminal. Think about it and you'll hopefully understand, why your previously used method can't work.

Regarding manuals, there's also an option to disable autobaud and store the setting permanently. You should also consider the case, that the modem may have been set to a different fixed baudrate before.