Unable to read AT response using UNO with GPRS Shield with SIM900

Hello, I am unable to send and receive AT commands, below is what I have done so far:

2 - SIM Cards
1 - Arduino Uno
2 - GPRS Shields
1- GPRS Shield v2.1 from Seed Studio
1 - GPRS model SLD33149P
Connected External Power Supply along with the USB connection
According to LEDs both connect to the network
2 Workstations
1 - XP
1 - Win 7
3 Communication Applications
Arduino Serial Monitor
Com Port Settings - default 19200 8-N-1
All speed combinations have been tried

Here is what happens when I turn on the Shield with all three:

SSCOM 3.2:



Arduino Serial Monitor:
ÿÿÿÿÿÿÿÿæ ZL©Çá
ŠjZþýøúh*‹‹ š•cf{OJ

When I attempt to enter AT commands, nothing happens or unreadable characters are received.

In addition I have tried multiple reset attempts for both the GPRS and Ardunio.

The goal is to send SMS messages, no voice.

Any help would be greatly appreciated.

Thank you

Looks like an incorrect baud rate. Try other speeds.

That is what I thought as well however I tried multiple speeds. When attached to com port it defaults to 9600. Which I used. Then reading forums and sample sketchs I tried 19200 and used some of the sample code. But again no change. Did I overlook something?

That is what I thought as well however I tried multiple speeds. When attached to com port it defaults to 9600. Which I used. Then reading forums and sample sketchs I tried 19200 and used some of the sample code. But again no change. Did I overlook something?

Did you try every speed?
How exactly is the GPRS Shield connected to your PC?

USB cable to the UNO

USB cable to the UNO.

Did you not want help figuring out your mistake? I asked how the GPRS Shield was connected to the PC. You gave me an answer for the Arduino UNO. How is data getting from Pin 0 and Pin 1 of your Arduino UNO to the serial pins of the GPRS shield?!?

I apologize if I didn't answer it correctly you can probably tell I am new to this. The GPRS shield is plugged into the top of the UNO using the pins from the board as shown on the form documentation. No additional wires are connected between the GPRS and UNO. You are correct the USB cable is connected from the PC to the UNO.

Try the link in my signature. It might help you set it up correctly.

Dannable, I did everything outlined in the link including uploading the Test sketch with no change. I also switched GPRS to the SLD01098P which connects to the network real fast but still unable to read responses from AT Commands. I must be overlooking something easy. Is it true the modem should respond to AT commands even when not on the network? Could I have somehow sent a command that changed how it responds? I never thought this would be that difficult. Thanks for your continued support.

Yes, it should be that simple! As long as you have the correct baud rate set for Serial (Arduino end) and on the Serial Monitor you should get some response when you type AT, even if it is 'OK'. You have got the jumpers set correctly haven't you? And just to be certain can you provide a link to the shield you have?

Factory reset is 'AT&F' (without the single quotes)

I am using GPRS Shield V2.0 as shown in this link http://www.seeedstudio.com/depot/gprs-shield-v20-p-1379.html?cPath=132_134. According to the documentation this GPRS can connect directly to the top of the UNO. The jumpers are set exactly as shown in the first image on the site. This board quickly connects to the network according to the 3 second delay in the LEDs. I will keep researching but I thought by now I would be past this and on to further testing.

At the risk of causing offence, did you have to solder the headers on yourself? If so check around pins D7 & D8.

If all else fails try removing the jumpers completely, and use wires to connect the centre two pins of the jumper block to two different digital pin headers and modify the call to SoftwareSerial to suit.

No problem with the questions. I am just thankful for the help. I will remove the jumpers and wire to other pins and try that. Do you recommend any pins so I don't step on top of anything else? The interesting thing is why do I experience the same issue on two GPRS shields.

D2 & D3 are popular with other shield manufacturers! But unless you have anything other than Arduino and shield there shouldn't be any conflict with anything else.

Ok I will try this evening and let you know.

I did not experience any change using this approach. I am at the point I will have to purchase a new board. The only thing I am not sure of do I purchase a new UNO or GPRS shield. Or do I purchase a package that has them both that I am sure will work together. Any input would be helpful. Thanks for taking the time.

For my 'permanent' installations I am currently using an Uno clone and a GPRS shield V1.1(B) with the web address www.epalsite.com printed on it (both from eBay). It really is 'plug and play'.

The shield is compact, has a hinged sim card holder (I don't like the slide in ones, they try to force the micro sim out), its I/O ports are configurable to a point and the aerial is detachable so can be easily attached to the wall of an enclosure.

Down sides are that there is no battery backup for the clock (not insurmountable but strange) and I would have preferred more Rx pin selection options. Tx has four, Rx two! But if I get stuck I can use wires as I suggested earlier.

Dannable. No change when I follow your steps. I think I am going to have to purchase either a new Uno or GPRS but I am not sure which one is causing my problem. I wonder if my AT&T SIM is locked. Would that cause what I am experiencing? The Arduino GPRS sold with a SIM always seem to be out of stock when I attempt to purchase.

Even without a sim card it should respond in a legible way to an AT command.

Do you get a response of any sort to 'at' in lower case letters?

Regardless of what is entered upper or lower case the echo back is always unreadable. This evening I will pull out the SIM and try again and let you know if the response.