SoftwareSerial Send Wrong data some times

**Hi there **

I'm trying to use the software serial library in my Arduino Nano projects with GSM SIM900 using pin 7 and 8 as software serial some times read wrong data

I am using this simple sketch :

#include <SoftwareSerial.h>
SoftwareSerial GSMModule(7, 8); // (Rx,Tx  > Tx,Rx)

void setup() {
  // put your setup code here, to run once:

void loop() {
  // put your main code here, to run repeatedly:
  while (GSMModule.available()) {

  while (Serial.available()) {

  if (GSMModule.overflow()) {
    Serial.println("SoftwareSerial overflow!");

Have a look at the examples in Serial Input Basics - simple reliable non-blocking ways to receive data. There is also a parse example to illustrate how to extract numbers from the received text.