How to send AT command to sim800l with SoftwareSerial

Question

I have SIM800l module connected to Arduino and I'm trying to initialize it in my setup function with this code:

#include <SoftwareSerial.h>
//SIM800 TX is connected to Arduino D8
#define SIM800_TX_PIN 6
//SIM800 RX is connected to Arduino D7
#define SIM800_RX_PIN 7
SoftwareSerial serialSIM800(SIM800_TX_PIN,SIM800_RX_PIN);
void setup()
{
 Serial.begin(38400);
 while(!Serial);
 serialSIM800.begin(38400);
 Serial.println("wait for .... it");
 delay(10000);
 // comments added just for example, both commands return junk
 //serialSIM800.write("AT\r\n"); 
 //serialSIM800.write("AT+SAPBR=3,1,\"Contype\",\"GPRS\"\r\n");
 Serial.println("command sent");
 delay(2500);
 Serial.write(serialSIM800.read());
}

But Serial.write returns junk.

When I use this code in 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());
 }

and send AT+SAPBR=3,1,"Contype","GPRS" or just AT command with serial monitor, everything works fine.

Can someone help with this?

• brtiberio: Can you place your schematic? Are you using the 4V regulation and transistor on RST pin? Maybe this library might help
• Nick Gammon: What sort of junk? Copy and paste please. Also writing the output from a read, without testing for available is likely to return "junk" or at least ÿ.
• SoreDakeNoKoto: You're reading only a byte like others have noted. Also, you seem to be sending 2 commands, one immediately after the other. This could result in gibberish. Though it would be nice to see exactly what your 'junk' results are.
• Nick Gammon: I'm a bit surprised you have put a bounty of +100 rep on this question, but are not answering queries like the comments above, that might help resolve it.

Answer 1

You can try to use serialSIM800.println("AT") instead of write. Here some examples https://github.com/stanleyhuangyc/Freematics/issues/17

Answer 2

NeoSWSerial would be better for this. It can read and write at the same time, unlike SoftwareSerial, and it doesn't disable interrupts for the entire character receive time (~1ms!). AltSoftSerial would be even better, but you can only use it on pins 8 & 9 (on an UNO, different pins on other Arduinos).

Answer 3

Somewhere you said that ...but Serial.write return's junk.... Make sure that serial print is Both NL & CR

Answer 4

You are getting junk because of baud rate, set as 9600.

Serial.begin(9600); while(!Serial); serialSIM800.begin(9600); Serial.println("wait for .... it"); delay(10000);

Answer 5

IIRC, SIM800 modems are very 1990s, they default to 9600 baud. You will get garbage at 38400.

I successfully used a SIM800 at 9600.

Answer 6

My SIM808 returns a bit of junk right from the get-go, so that might be influencing things.

Also, it's conceivable you are retrieving a -1 from your initial serialSIM800.read() call - it's a nonblocking call and returns -1 when no data is available. That would almost definitely appear as junk.

Answer 7

Sim800 series free Atcommander software.

http://bayanbox.ir/info/3493267131357723232/ATcenter