# SIM800L doesn't respond to AT commands **URL:** \ **Category:** General Guidance\ **Created:** [June 29, 2023, 8:32pm UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086 "2023-06-29T20:32:46Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![suliss03](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suliss03/32/981885_2.png) [@suliss03](https://forum.arduino.cc/u/suliss03)\ **Post date:** [June 29, 2023, 8:32pm UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/1 "2023-06-29T20:32:46Z")
Hi. My SIM800L doesn't respond to AT command. The serial monitor is simply blank And the led blinks every 3 seconds wich means its connected to a network I power it trough a lm2596 buck down converter with 4.0 v (I've tried to power with voltages until 4.4v) , From a 12v power suply Can you help me ? (Please keep in mind that I'm a absolute beginner in this field. Thanks) I used this wiring diagram from last minute engineers ![Arduino-Wiring-Fritzing-Connections-with-SIM800L-GSM-GPRS-Module-LM2596](https://europe1.discourse-cdn.com/arduino/original/4X/0/f/a/0fafdaed0c9acd849c067349294aae44d596193e.png) And also their code: ```arduino #include SoftwareSerial mySerial(3, 2); void setup() { Serial.begin(9600); mySerial.begin(9600); Serial.println("Initializing..."); delay(1000); mySerial.println("AT"); updateSerial(); mySerial.println("AT+CMGF=1"); updateSerial(); mySerial.println("AT+CNMI=1,2,0,0,0"); updateSerial(); } void loop() { updateSerial(); } void updateSerial() { delay(500); while (Serial.available()) { mySerial.write(Serial.read()); } while(mySerial.available()) { Serial.write(mySerial.read());} } ``` ---
**Author:** ![Railroader](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/railroader/32/274550_2.png) [@Railroader](https://forum.arduino.cc/u/Railroader)\ **Post date:** [June 29, 2023, 8:55pm UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/2 "2023-06-29T20:55:43Z")
4.0 volt? What does the SIM card spec say? What's the value of the resistors? Why do You need double line spacing in the code? It makes the view being half the number of lines. ---
**Author:** ![xfpd](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/xfpd/32/1120236_2.png) [@xfpd](https://forum.arduino.cc/u/xfpd)\ **Post date:** [June 29, 2023, 9:03pm UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/3 "2023-06-29T21:03:27Z")
> [@Railroader](#): > > double line spacing An artifact from code lifted from HTML or PDF. ---
**Author:** ![Railroader](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/railroader/32/274550_2.png) [@Railroader](https://forum.arduino.cc/u/Railroader)\ **Post date:** [June 29, 2023, 9:14pm UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/4 "2023-06-29T21:14:26Z")
Not wanted.... ---
**Author:** ![suliss03](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suliss03/32/981885_2.png) [@suliss03](https://forum.arduino.cc/u/suliss03)\ **Post date:** [June 29, 2023, 10:05pm UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/6 "2023-06-29T22:05:41Z")
I apologize for the double lines. i'll fix them right away. As for the resistores their values are 10k and 20k According to the SIM800l Datasheet The module can be powered with Power supply of 3.4V ~4.4V and The SIM interface is powered from an internal regulator in the module. ---
**Author:** ![Railroader](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/railroader/32/274550_2.png) [@Railroader](https://forum.arduino.cc/u/Railroader)\ **Post date:** [June 30, 2023, 5:53am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/7 "2023-06-30T05:53:57Z")
Thank You. That looks good. Due to a travel I'll have to step aside for 2 days..... ---
**Author:** ![suliss03](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suliss03/32/981885_2.png) [@suliss03](https://forum.arduino.cc/u/suliss03)\ **Post date:** [July 4, 2023, 11:28am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/8 "2023-07-04T11:28:02Z")
I understand. ---
**Author:** ![awneil](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@awneil](https://forum.arduino.cc/u/awneil)\ **Post date:** [July 4, 2023, 11:32am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/9 "2023-07-04T11:32:50Z")
> [@suliss03](#): > > My SIM800L doesn't respond to AT command Have you tried it direct to a serial terminal - ie, take the Arduino and your code out of the equation? Please give some more details of the board that the SIM800L is on - in particular, its pinout. A link to specs would help. > [@suliss03](#): > > I used this wiring diagram from last minute engineers Have you contacted them for help? A link to their page? ---
**Author:** ![Railroader](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/railroader/32/274550_2.png) [@Railroader](https://forum.arduino.cc/u/Railroader)\ **Post date:** [July 4, 2023, 11:52am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/10 "2023-07-04T11:52:50Z")
You copy every character coming in Serial.read out to software serial. Add some Serial.print telling exactly what characters are transfered. I suspect Cr and/or Lf might be passing, and maybe ruin the AT comand syntax. ---
**Author:** ![suliss03](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suliss03/32/981885_2.png) [@suliss03](https://forum.arduino.cc/u/suliss03)\ **Post date:** [July 5, 2023, 1:14am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/11 "2023-07-05T01:14:00Z")
I'm really new at this. And i don't know what a serial terminal is, but ill try to look it up in order to use it. The board the SIM800L is on is the Arduino Uno Board: [Arduino specs and pinout](https://docs.arduino.cc/hardware/uno-rev3) And yes, i sent them a email. still waiting for response [Lastminuteengineers](https://lastminuteengineers.com/sim800l-gsm-module-arduino-tutorial/) ---
**Author:** ![suliss03](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/suliss03/32/981885_2.png) [@suliss03](https://forum.arduino.cc/u/suliss03)\ **Post date:** [July 5, 2023, 1:14am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/12 "2023-07-05T01:14:41Z")
Ok, ill try that and get back to you! ---
**Author:** ![Railroader](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/railroader/32/274550_2.png) [@Railroader](https://forum.arduino.cc/u/Railroader)\ **Post date:** [July 5, 2023, 6:06am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/13 "2023-07-05T06:06:34Z")
Your code uses Serial.read for the data into the controller. Are You sending those characters from serial monitor in the IDE? That was my assumption... Then a Serial.print can be used to print the hexadecimal representation of the characters handled. ---
**Author:** ![awneil](https://avatars.discourse-cdn.com/v4/letter/a/49beb7/32.png) [@awneil](https://forum.arduino.cc/u/awneil)\ **Post date:** [July 5, 2023, 9:05am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/14 "2023-07-05T09:05:46Z")
> [@suliss03](#): > > i don't know what a serial terminal is A program like [RealTerm](https://sourceforge.net/projects/realterm/) or [TeraTerm](https://ttssh2.osdn.jp/index.html.en) (to name but two) - or even the Arduino IDE's Serial Monitor - which lets you send & receive characters over a serial interface (a "`COM` port" on Windows; "`/dev/tty`" on Linux). Characters you type at the keyboard are sent to the serial interface; characters received from the serial port are displayed on the screen. This allows you to manually interact with any serial device. ADDENDUM Sometimes also called a "_Terminal Emulator_" - because it emulates the behaviour of the old, dedicated serial terminals: ![image](https://europe1.discourse-cdn.com/arduino/original/4X/f/8/7/f87c3ba6121e82fe4171a5fb5fe028f477753b78.jpeg) ---
**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:** [January 1, 2024, 9:05am UTC](https://forum.arduino.cc/t/sim800l-doesnt-respond-to-at-commands/1143086/15 "2024-01-01T09:05:47Z")
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