SIM800 does not reply to AT commands

Projects Networking, Protocols, and Devices
1

Hi, i have this board

http://www.ebay.com/itm/181891664820?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

i am using that code

#include <SoftwareSerial.h>
 
//SIM800 TX is connected to Arduino D8
#define SIM800_TX_PIN 8
 
//SIM800 RX is connected to Arduino D7
#define SIM800_RX_PIN 7
 
//Create software serial object to communicate with SIM800
SoftwareSerial serialSIM800(SIM800_TX_PIN,SIM800_RX_PIN);
 
void setup() {
  //Begin serial comunication with Arduino and Arduino IDE (Serial Monitor)
  Serial.begin(9600);
  while(!Serial);
   
  //Being serial communication witj Arduino and SIM800
  serialSIM800.begin(9600);
  delay(1000);
   
  Serial.println("Setup Complete!");
}

void loop() {
  //Read SIM800 output (if available) and print it in Arduino IDE Serial Monitor
  if(serialSIM800.available()){
    Serial.write(serialSIM800.read());
    
  
  }
  //Read Arduino IDE Serial Monitor inputs (if available) and send them to SIM800
  if(Serial.available()){    
    serialSIM800.write(Serial.read());
 
  }
}

the SIM card is ok since the leds are blinking correctly and the unit seems to be in network ( ringing if you call it_)

The promblem is that the Serial monitor does nto accept any AT command, it does not reply to any of them

i activate NL & CR but nothing change

Any idea ?

Thanks

2

A few questions? How did you power up your SIM module? I had s similar problem. Please describe in details, or, even better, with a photo or schematic.

If you are using external power (other that arduino power), try connecting arduino GND and external power GND. It worked for me

3

Hi My Dear Friend,

i connect the module with external power of 12v, i also add a common Gnd BETWEEN THE power unit and the arduino .

here is my scheme ...

Untitled.png
Untitled.png1487×700 202 KB

4

12V? I'm not sure if that module has a voltage regulator or not, but I think the SIM modules are supposed to be powered with voltages around 4V DC.

this is copied from the sim800 datasheet regarding powering the module:

The power supply range of SIM800 is from 3.4V to 4.4V. Recommended voltage is 4.0V. The transmitting burst
will cause voltage drop and the power supply must be able to provide sufficient current up to 2A. For the VBAT
input, a bypass capacitor (low ESR) such as a 100µF is strongly recommended.