Arduino - garbled serial output

Question

I've hooked up a ADH8066 (Sparkfun) GSM Module to my Arduino Uno, and am trying to get some correct serial going between the Arduino and the GSM module. It works fine when I connect to it directly (via USB or just the TTL lines) but not when being controlled via the Arduino. Some text will output correctly, the rest will be garbled, almost as if the baud rate is wrong, but I'm just using the same baud (115200) I do as when I connect from a PC.

Here is the Arduino code I'm using:

#include <SoftwareSerial.h>

#define rxPin 7
#define txPin 8
SoftwareSerial mySerial = SoftwareSerial(rxPin, txPin);

// EN: String buffer for the GPRS shield message
String SmsStorePos = String("");
String msg = String("");
String snTmp = String("");
String snFull = String("");

// EN: Set to 1 when the next GPRS shield message will contains the SMS message
int SmsContentFlag = 0;

// EN: Pin of the LED to turn ON and OFF depending on the received message
int ledPin = 5;
int powerPin = 6;

void setup()
{
  mySerial.begin(115200);               // the GPRS baud rate   
  mySerial.print("\r");
  delay(1000);
  Serial.begin(115200);                 // the Arduino IDE serial
  Serial.println("Started!");

  pinMode( ledPin, OUTPUT ); 
  digitalWrite( ledPin, LOW ); 

  pinMode( powerPin, OUTPUT);
  digitalWrite(powerPin, LOW);    // brings ONKEY low to turn on the modem (aka pressing the ONKEY)
  delay(3000);
  digitalWrite(powerPin, HIGH);    // sets the pin HIGH again (restore 5V)
  delay(5000);

  // test LED pin
  digitalWrite ( ledPin, HIGH);
  delay(1000);
  digitalWrite( ledPin, LOW); 
}

void loop()
{
    char SerialInByte;

    // Send anything we receive from the IDE to the modem
    if(Serial.available())
    {
       mySerial.print((unsigned char)Serial.read());
     }  
    else  if(mySerial.available())
    {
        char SerialInByte;
        SerialInByte = (unsigned char)mySerial.read();
        //SerialInByte = mySerial.read();

        // EN: Relay to Arduino IDE Monitor
        Serial.print( SerialInByte );

        // -------------------------------------------------------------------
        // EN: Program also listen to the GPRS shield message.
        // -------------------------------------------------------------------

        // EN: If the message ends with <CR> then process the message
        if( SerialInByte == 13 ){
          // EN: Store the char into the message buffer
          ProcessGprsMsg();
         }
         if( SerialInByte == 10 ){
            // EN: Skip Line feed
         }
         else {
           // EN: store the current character in the message string buffer
           msg += String(SerialInByte);
         }
     }   
}

// EN: Make action based on the content of the SMS. 
//     Notice than SMS content is the result of the processing of several GPRS shield messages.
void ProcessSms( String sms ){
  sms.toLowerCase();
  Serial.print( "ProcessSms for [" );
  Serial.print( sms );
  Serial.println( "]" );

  if( sms.indexOf("on") >= 0 ){
    digitalWrite( ledPin, HIGH );
    Serial.println( "LED IS ON" );
    return;
  }
  if( sms.indexOf("off") >= 0 ){
    digitalWrite( ledPin, LOW );
    Serial.println( "LED IS OFF" );
    return;
  } else {
    mySerial.print("AT+CMGF=1\r");    //Because we want to send the SMS in text mode
    delay(1000);
    mySerial.print("AT+CMGS=\"");
    mySerial.print(snFull);
    mySerial.print("\"\r");
    delay(1000);
    mySerial.print("Unknown Command: ");
    mySerial.print(sms);
    mySerial.print("\r");
    delay(1000);
    mySerial.write(0x1A);  //Equivalent to sending Ctrl+Z     
    return;
  }
}
// EN: Request Text Mode for SMS messaging
void GprsTextModeSMS(){
  mySerial.println( "AT+CMGF=1" );
}

void GprsReadSmsStore( String SmsStorePos ){
  // Serial.print( "GprsReadSmsStore for storePos " );
  // Serial.println( SmsStorePos ); 
  mySerial.print( "AT+CMGR=" );
  mySerial.println( SmsStorePos );
}

// EN: Clear the GPRS shield message buffer
void ClearGprsMsg(){
  msg = "";
}

// EN: interpret the GPRS shield message and act appropiately
void ProcessGprsMsg() {
  Serial.println("");
  Serial.print( "GPRS Message: [" );
  Serial.print( msg );
  Serial.println( "]" );

  if( msg.indexOf( "Call Ready" ) >= 0 ){
     Serial.println( "*** GPRS Shield registered on Mobile Network ***" );
     GprsTextModeSMS();
  }

  // EN: unsolicited message received when getting a SMS message
  if( msg.indexOf( "+CMTI" ) >= 0 ){
     Serial.println( "*** SMS Received ***" );
     // EN: Look for the coma in the full message (+CMTI: "SM",6)
     //     In the sample, the SMS is stored at position 6
     int iPos = msg.indexOf( "," );
     SmsStorePos = msg.substring( iPos+1 );
     Serial.print( "SMS stored at " );
     Serial.println( SmsStorePos );

     // EN: Ask to read the SMS store
     GprsReadSmsStore( SmsStorePos );
  }

  // EN: SMS store read via UART (result of GprsReadSmsStore request)  
  if( msg.indexOf( "+CMGR:" ) >= 0 ){
    // get number of sender
    int snPos = msg.indexOf("+1");
    Serial.print("SMS From: ");
    snTmp = msg.substring(snPos+1);
    snFull = "";
    for (int i = 0; i < 11; i++){
      snFull += snTmp[i];    
    }
    Serial.println(snFull);

    // EN: Next message will contains the BODY of SMS
    SmsContentFlag = 1;
    // EN: Following lines are essentiel to not clear the flag!
    ClearGprsMsg();
    return;
  }

  // EN: +CMGR message just before indicate that the following GRPS Shield message 
  //     (this message) will contains the SMS body
  if( SmsContentFlag == 1 ){
    Serial.println( "*** SMS MESSAGE CONTENT ***" );
    Serial.println( msg );
    Serial.println( "*** END OF SMS MESSAGE ***" );
    ProcessSms( msg );
    delSMS();
  }

  ClearGprsMsg();
  // EN: Always clear the flag
  SmsContentFlag = 0; 
}
void delSMS() {
  mySerial.print("AT+CMGD=");
  mySerial.println(SmsStorePos);
}  

Below is what I'm seeing in the serial monitor:

Answer 1

Make sure the "baud" setting matches your sketch.

Ex: Serial.begin(115200); >>>> 115200 baud in the console.

I got this solution out of a comment above from kunalbhat. But I wanted to post it as a stand-alone answer because it solved my problem, and it would have never occurred to me. So I think it will help a lot of other people.

Answer 2

SoftwareSerial is notoriously picky about timing and will cause problems like you describe when "too much" is going on at the same time. It probably gets out of sync because of you are doing other stuff on the side.

I warmly recommend AltSoftSerial (http://www.pjrc.com/teensy/td_libs_AltSoftSerial.html), which performs much better, but I still suggest you use slightly lower baud rates to increase reliability. Too high baud rates will require very exact timing to not miss a single bit and the hardware is not powerful enough to do serial traffic in software without problems.

Answer 3

As was said before, the issue is with the "baud" setting (which has to do with serial communication- another answer). This can be found (typically) at the top of your sketch, and might look like this:

Serial.begin(9600);

Or this:

Serial.begin(115200);

In the case of an Arduino Uno, a "baud" setting other than 9600 will result in garbled text. As such, make sure that at the beginning of your sketch, you have the line:

Serial.begin(9600);

Feel free to ask if you need any further help.