GSM module connected with arduino uno giving garbage values in response

Question

I connected a GSM module with the Arduino UNO. The connections are as follows:

Gnd of gsm -----> Gnd of arduino

TX of gsm -----> pin 9 of arduino

Rx of gsm -----> pin 10 of arduino

GSM is powered from a 9V-1Amp wall adapter.

The GSM is performing according to all the AT commands (like making a voice call, hanging a call, answering a call) which are given, but it is displaying garbage values on serial monitor in response.

Here is the code:

#include <SoftwareSerial.h>
SoftwareSerial myserial(9, 10);
void setup() {
 Serial.begin(115200);
 myserial.begin(9600);
 myserial.println("ATDXXXXXXXXXX;");
 delay(30000);
 myserial.println("ATH");
}
void loop() {
 if (myserial.available()>0){
 Serial.println(myserial.read());
 }
}

What could be reasons for the GSM to output garbage values and how can I resolve it?

• Majenko: 115200 baud is at the top end of what software serial can handle. It's probably failing miserably. Better to use hardware serial on a board with multiple UARTs.
• jfpoilpret: @Majenko from the code, the OP is using SoftwareSerial at only 9600 then that should be fine.
• Majenko: @jfpoilpret It was hard to tell since the code was such a mess. Yes, I could have formatted it myself, but that's the job of the OP to do. If they can't even be bothered to do that, then... meh...
• jfpoilpret: Could you post the garbage (and its value in hexadecimal if unprintable) you get?

Answer 1

 Serial.println(myserial.read());

myserial.read() returns an integer. That integer is either the ASCII code of the next character in the buffer, or -1 if there is no character to read.

You then print that integer, each one on its own line.

So the response "OK\r\n" from, say, "AT\r\n" would look like:

79
75
13
10

Instead you need to write the data, not print it:

Serial.write(myserial.read());

Also, the way you have written your code, you will get no response for 30 seconds - that is, until everything has already happened. Only after it has all finished will you get some feedback - and that may not be complete since you may overrun the buffer depending on what the modem sends.

• user22930: I tried using Serial.write() in place of Serial.println() but still I am getting the garbage values. The module is not responding even while sending an AT command through Serial Monitor.