Hello friends, I have an Arduino UNO R3 and a GPRS shield SIM900D. I connected the UNO gave the shield GPRS download program that prepares one to send AT commands to the GPRS, but can not send any commands to the GPRS, I get only the information below in the serial monitor:

???? RDY

  • CFUN: 1


  • PACSP: 1

Call Ready

And it is, I can not send any AT command. I'm utiizando 12V supply to power the Arduino UNO. I'm using the library SoftwareSerial in IDE 1.0

Efetuei voltage measurements, and obtained the following results:

Pin => Stress

Vin => 12V 5V => 5V 3.3 V => 0.0015 V (*)

As above, the pin 3.3 V not getting the expected voltage, is that this may be the reason for me not being able to send AT commands to the GPRS shield?

When I type in AT Serial Monitor and click on SEND, the RX LED flashes on the Arduino UNO, but I do not get any return. The Serial Monitor is configured as "Carriage Return" with baud rate of 9600, as put in the code. I appreciate the help!

Hello! I bought the same thing as you and I was trying to make a call but when I did according to the Wiki, I always got "serial port error". The thing is I am using Port 3 for Arduino but the hint never stopped. How did you make the call? Can you give me some websites or video link that I can take a look at?


connect pin 7 to 10 and pin 8 to 11 and try once.