SIM900A not receiving/transmitting data

[ruben24]

I am using SIM900A GSM module to send sms/make calls . I use an external power supply (4 batteries) and a step down buck converter to adjust the voltage to 5V . The issue now is , when the led on GSM module has been blinking every 1/2 seconds , it was able to transmit data to my Arduino UNO ( Responds "OK" to "AT" command) . But when I provide external power supply and the led now blinks every 3 second (indicating connection to network) , it is now no more able to transmit data to my Arduino .

Below is the code I use for debugging :

#include <SoftwareSerial.h>

// Create software serial object to communicate with SIM800L
SoftwareSerial mySerial(3, 2); // GSM Module Rx & Tx is connected to Arduino #2 & #3

void setup() {
  Serial.begin(9600);
  while (!Serial) {
    ; 
  }
  Serial.println("Serial communication started");
  mySerial.begin(9600);
  Serial.println("SIM800L communication started");
}

void loop() {
  // Forward data from Serial Monitor to GSM module
  while (Serial.available()) {
    char inByte = Serial.read();
    Serial.print("Sending to GSM: ");
    Serial.println(inByte);
    mySerial.write(inByte);
  }

  // Forward data from GSM module to Serial Monitor
  while (mySerial.available()) {
    char inByte = mySerial.read();
    Serial.print("Received from GSM: ");
    Serial.println(inByte);
    Serial.write(inByte);
  }
}

When the network is connected ( led blinks every 3s) , serial monitor is not able to print out "Received from GSM" for AT command . However , when the led blinks every 1/2 s , it is able to print out "Received from GSM" . I really cannot understand what's going on , please help .

[liaifat85]

SIM900A needs 5V, 2A power supply. Are your batteries outputting 2A?

[xfpd]

@ruben24

Serial.println("SIM800L

Your title says SIM900A.

[sibirean_bear]

Hello freands!
If you have trouble with communicate to SIM900A perhaps you have the same trouble like me. You need to delete from plate R8 and R9 resistor, and it begins work perfectly !