Sending AT commands to a GSM/GPRS and displaying the reply on a Serial Monitor

Question

I am quite rusty when it comes to Serial ports. I want to send an AT command to a GSM/ GPRS shield connected to my Arduino UNO. The AT command I want to pass in particular is the command to get a networks signal strength.

I am using the SIM900 and SoftwareSerial library to send the command as the GSM library does not compile correctly for me. Meaning I have to use the SoftwareSerial library.

I have this example code from the SIM900 library working that relies on reading inputs from the serial monitor to carry out commands but I need it to be automated and the command to be passed in hardcoded. In this example code, the place of interest is the simplehwread() method.

#include "SIM900.h"
#include <SoftwareSerial.h>

int numdata;
char inSerial[40];
int i=0;

void setup()
{
     //Serial connection.
     Serial.begin(9600);
     Serial.println("GSM Shield testing.");
     //Start configuration of shield with baudrate.
     //For http uses is raccomanded to use 4800 or slower.
     if (gsm.begin(9600))
          Serial.println("\nstatus=READY");
     else Serial.println("\nstatus=IDLE");
};

void loop()
{
     //Read for new byte on serial hardware,
     //and write them on NewSoftSerial.
     serialhwread();
     //Read for new byte on NewSoftSerial.
     serialswread();
};

void serialhwread()
{
     i=0;
     if (Serial.available() > 0) {
          while (Serial.available() > 0) {
               inSerial[i]=(Serial.read());
               delay(10);
               i++;
          }

          inSerial[i]='\0';
          if(!strcmp(inSerial,"/END")) {
               Serial.println("_");
               inSerial[0]=0x1a;
               inSerial[1]='\0';
               gsm.SimpleWriteln(inSerial);
          }
          //Send a saved AT command using serial port.
          if(!strcmp(inSerial,"TEST")) {
               Serial.println("SIGNAL QUALITY");
               gsm.SimpleWriteln("AT+CSQ");
          } else {
               Serial.println(inSerial);
               gsm.SimpleWriteln(inSerial);
          }
          inSerial[0]='\0';
     }
}

void serialswread()
{
     gsm.SimpleRead();
}

No matter how I modify this code, the command does not get passed in and response displayed while the method here does it but not the way I want it to be done. i.e Direct input. Could anyone assist here?

Mr.Pibb64 Mr.Pibb64 · Accepted Answer · 2016-06-05T23:30:53

i have dealt with exactly this scenario at a company with a cellular radio on board. there are many status signals that come over and if not dealt with appropriately these status flags from the cell modem will be lost

you need to look at the data sheets associated with your cell modem and its protocol so you know what flags to watch for at the various steps taken along the way from configuration, to eventual connection to cellular service.

multi-threaded coding techniques must be followed as well.

keep in mind that the comm channel is not ideal and there WILL be failures. provided your coding techniques are sound and you follow protocol requirements, then it should work.

Ron Boise, ID

Sending AT commands to a GSM/GPRS and displaying the reply on a Serial Monitor

1 Answers