GPRS failed to connect using Arduino Mega2560

Need Help

I’m using SIM900a to connect to Blynk using Arduino Mega but it always showed “connect to GPRS failed”. But when i;m using the Arduino Uno it works. I changed to Mega because my overall code sketch is too big for Uno. My code here is just to make sure the SIM900a can connect to Blynk.

I’m too confused

#define BLYNK_PRINT Serial

/* Fill in information from Blynk Device Info here */
#define BLYNK_TEMPLATE_ID "TMPxxxxx"
#define BLYNK_TEMPLATE_NAME "Device"

// Select your modem:
//#define TINY_GSM_MODEM_SIM800
//#define TINY_GSM_MODEM_M590
//#define TINY_GSM_MODEM_A6
//#define TINY_GSM_MODEM_A7
//#define TINY_GSM_MODEM_BG96

// Default heartbeat interval for GSM is 60
// If you want override this value, uncomment and set this option:

#include <TinyGsmClient.h>
#include <BlynkSimpleTinyGSM.h>
#include <MQ7.h>

// Your GPRS credentials
// Leave empty, if missing user or pass
char apn[]  = "internet";
char user[] = "";
char pass[] = "";

// Hardware Serial on Mega, Leonardo, Micro
#define AVR_ATmega328P
#define SerialAT Serial1

TinyGsm modem(SerialAT);
const int mq7Pin = A0;

void setup()
  // Debug console


  // Set GSM module baud rate

  // Restart takes quite some time
  // To skip it, call init() instead of restart()
  Serial.println("Initializing modem...");

  // Unlock your SIM card with a PIN

  Blynk.begin(BLYNK_AUTH_TOKEN, modem, apn, user, pass);

void loop()
  float coLevel = readMQ7(); // Replace with your actual MQ7 sensor reading function
  Blynk.virtualWrite(V1, coLevel); // V1 is the virtual pin you associated with the Gauge widget in Blynk

   Serial.print("CO Level: ");
  Serial.println(" ppm");


float readMQ7()
 int sensorValue = analogRead(mq7Pin);
  float voltage = sensorValue * (5.0 / 1023.0);
  float coLevel = map(sensorValue, 0, 1023, 0, 100); // Assuming the MQ7 sensor outputs values from 0 to 100 ppm

  return coLevel;

The code you’ve posted above is incomplete, because it’s missing #define BLYNK_AUTH_TOKEN
That’s not a big deal, because it was clearly present in the actual code you uploaded, but when I see code that clearly can’t be compiled it rings alarm bells. What else have you changed before posting the code is the first question I ask myself.

Obviously your Uno code was significantly different because it would have needed to use SoftwareSerial. Posting the Uno version of this basic sketch, along with the serial output that it produces, plus the complete Mega version of the sketch and the resulting serial output would be a good starting point.
Explaining how you’ve connected and powered your SIM900a in both situations would also be useful.

On a different note, you should read this…

Because your current cluttered void loop and use of blocking delay() commands isn’t going to work well.