Solved GSM 900 sms ÿÿ0? error reading sms messages

Projects Programming
1

Hello i got get this error message in the serial monitor i send a sms text message from my cellphone to the arduino and before it reads the text message with no problem now i get this error ÿÿ0?ÿÿÿÿÿÿÿÿÿ can someone please help me out this is the sketch i used

#include <SoftwareSerial.h>
SoftwareSerial SIM900(7, 8);
 
char incoming_char=0;
 
void setup()
{
  Serial.begin(19200); // for serial monitor
  SIM900.begin(19200); // for GSM shield
  SIM900power();  // turn on shield
  delay(20000);  // give time to log on to network.
 
  SIM900.print("AT+CMGF=1\r");  // set SMS mode to text
  delay(100);
  SIM900.print("AT+CNMI=2,2,0,0,0\r");
  // blurt out contents of new SMS upon receipt to the GSM shield's serial out
  delay(100);
}
 
void SIM900power()
// software equivalent of pressing the GSM shield "power" button
{
  digitalWrite(9, HIGH);
  delay(1000);
  digitalWrite(9, LOW);
  delay(7000);
}
 
void loop()
{
  // Now we simply display any text that the GSM shield sends out on the serial monitor
  if(SIM900.available() >0)
  {
    incoming_char=SIM900.read(); //Get the character from the cellular serial port.
    Serial.print(incoming_char); //Print the incoming character to the terminal.
  }
}
2

Are you sure that you have the baud rates set correctly ?

3

hello yes in the serial monitor the same as in the sketch 19200 i never change nothing all of the sudden this happens

4

hello yes in the serial monitor the same as in the sketch 19200

But, is the GSM modem actually communicating at 19200? That's an unusual speed for a GSM modem.

5

in the sketch it haves this

Serial.begin(19200);
SIM900.begin(19200);

6

i did add that after i seen that message the SIM900.begin but came out to be the same thing. same message.

7

The examples I've seen, using a SIM900, use 2400 as the baud rate. It's interesting that you are using something much higher.

8

i know it is high but i didn't make the sketch and it's still giving me problem it was working again them went back to that ÿÿÿÿÿÿÿÿ stuff. should i put the sim900 at 2400 what about the Serial begin its set also at 19200?

9

I don't know about the GSM, but normally, Arduino functions return -1 when no characters are available from that device. That will display the funny y.
Funny y = ÿ = 255 = -1 = no characters available

10

PaulS:
The examples I've seen, using a SIM900, use 2400 as the baud rate. It's interesting that you are using something much higher.

A bit late, but the SIM900 documentation states that providing auto-bauding is turned on (that is the factory default) it will start communication at 115200 baud. You can over ride this by specifying a specific baud rate but I cannot see any advantage in that these days.

11

thank you dannable i will try that.

12

hello i tried that and at 115200 that seem to work i put sim900 at 115200 and the Serial.begin at 115200 and that seem to work better thank you.