# SIM800L is unresponsive to AT commands

**URL:** <https://forum.arduino.cc/t/sim800l-is-unresponsive-to-at-commands/1243402>\
**Category:** GSM Shield\
**Created:** [April 3, 2024, 12:36pm UTC](https://forum.arduino.cc/t/sim800l-is-unresponsive-to-at-commands/1243402 "2024-04-03T12:36:32Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![mohammedlotfy](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/mohammedlotfy/32/1058301_2.png) [@mohammedlotfy](https://forum.arduino.cc/u/mohammedlotfy)\
**Post date:** [April 3, 2024, 12:36pm UTC](https://forum.arduino.cc/t/sim800l-is-unresponsive-to-at-commands/1243402/1 "2024-04-03T12:36:32Z")

</div>

SIM800L connected to Arduino UNO doesn't respond to AT command.  
The serial monitor stops at  
"initializing..."

the LED blinks every 3 seconds  
VDD --\> connected to 5v of the Arduino uno

What should I do?

```arduino
#include <SoftwareSerial.h>

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

void setup()
{
  //Begin serial communication with Arduino and Arduino IDE (Serial Monitor)
  Serial.begin(9600);
  
  //Begin serial communication with Arduino and SIM800L
  mySerial.begin(9600);

  Serial.println("Initializing...");
  delay(1000);

  mySerial.println("AT"); //Once the handshake test is successful, it will back to OK
  updateSerial();
  mySerial.println("AT+CSQ"); //Signal quality test, value range is 0-31 , 31 is the best
  updateSerial();
  mySerial.println("AT+CCID"); //Read SIM information to confirm whether the SIM is plugged
  updateSerial();
  mySerial.println("AT+CREG?"); //Check whether it has registered in the network
  updateSerial();
}

void loop()
{
  updateSerial();
}

void updateSerial()
{
  delay(500);
  while (Serial.available()) 
  {
    mySerial.write(Serial.read());//Forward what Serial received to Software Serial Port
  }
  while(mySerial.available()) 
  {
    Serial.write(mySerial.read());//Forward what Software Serial received to Serial Port
  }
}

```

---

<div class="post-metadata">

**Author:** ![J-M-L](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/j-m-l/32/766245_2.png) [@J-M-L](https://forum.arduino.cc/u/J-M-L)\
**Post date:** [April 3, 2024, 12:51pm UTC](https://forum.arduino.cc/t/sim800l-is-unresponsive-to-at-commands/1243402/2 "2024-04-03T12:51:15Z")

</div>

> [@mohammedlotfy](#):
>
> VDD --\> connected to 5v of the Arduino uno

Did you connect Rx and Tx and GND ? did you make sure your SIM800 supports 5V on those pins?

Your SIM800L needs at least 1A at peak usage. If you power your arduino UNO through USB you won't get that (only 500mA)

it's not a good idea to power current hungry devices from the Arduino itself. Get a separate, good quality power supply for your SIM800

PS/ you posted in the Arduino GSM shield category. is this really what you have ??

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<div class="post-metadata">

**Author:** ![mohammedlotfy](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/mohammedlotfy/32/1058301_2.png) [@mohammedlotfy](https://forum.arduino.cc/u/mohammedlotfy)\
**Post date:** [April 3, 2024, 1:16pm UTC](https://forum.arduino.cc/t/sim800l-is-unresponsive-to-at-commands/1243402/3 "2024-04-03T13:16:10Z")

</div>

Thank you for your response  
I will use DC-DC buck converter

yes I have connected Rx and Tx and GND

But I though if the led blink every 3 seconds the problem is not about power supply

sorry, I'm an absolute beginner  
what category should I post it?

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<div class="post-metadata">

**Author:** ![J-M-L](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/j-m-l/32/766245_2.png) [@J-M-L](https://forum.arduino.cc/u/J-M-L)\
**Post date:** [April 3, 2024, 2:35pm UTC](https://forum.arduino.cc/t/sim800l-is-unresponsive-to-at-commands/1243402/4 "2024-04-03T14:35:45Z")

</div>

You are right, when the SIM800 module blinks every 3 seconds, it usually indicates that the module is registered to the network and is in standby mode so it had enough current to connect.

are you sure your SIM800L supports 5V for Serial?

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<div class="post-metadata">

**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\
**Post date:** [September 30, 2024, 2:35pm UTC](https://forum.arduino.cc/t/sim800l-is-unresponsive-to-at-commands/1243402/5 "2024-09-30T14:35:58Z")

</div>

Closed on September 30, 2024, 2:35pm UTC

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