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Topic: SIM800L module GSM not responding any answer on UART (Read 57 times) previous topic - next topic


Oct 27, 2020, 03:44 pm Last Edit: Oct 27, 2020, 05:34 pm by jimakoskx
I am new generally on arduino ......

I bought two SIM800L different modules and i am trying just to communicate in UART
from my fake/clone arduino uno r3
via SoftwareSerial.h   from my Arduino IDE 1.8.13
but i cant. (not even the OK answer from the simple AT command)

The code is very simple , is copied from the same place that i copied the image,
and i am posting it at the end.

When Sim800l module is powered on it finds network (all good)
( "i know" because i am calling from onother cellphone to the SIM card installed on module
and just does not answering)

I can think some reason and be welcome if someone wants to help me because i have beehive sms scale code ready

-I burned the  Rx/|&Tx
pin of the SIM800L module because i didnt from beginning DECREASE
the voltage from 5 Volts to -> ~3.3 volts that the manual of sim800l says that can handle.
See also at https://forum.arduino.cc/index.php?topic=508723.0
"The way I understand it, the SIM800L needs between 3.7v and 4.2v @ 2amps to function, which I have. The 2 wires that come from the arduino, in this case D8 (RX) and D9 (TX) need to be converted down into 2.8v using a logic level shifter / converter"

ENEN THOUGHT......the module can still can got in to cell phone network
because ITS RX/TX pins no need for that !

-The same problem i was having with the first SIM800L module
(different module same chip)
but .... i ve managed to send SMS  from that ! ...  
...EVEN IF i did NOT managed to get ANY replay like "OK" from sim module.
Meaning i could send sms but not reading answers(from any command by arduino to sim module)

-Thats why i am trying to ask here if someone knows
the possibility of HAVING fault on UART communication
from my arduino CLONE ?
I mean ... might be the case that my arduino is fake and not original?  

-Or if there is some problem with SoftwareSerial library ?
(baud rate-sync problems)
(that my new on Arduino eye felt somewhere on the internet)

Code: [Select]

byte PinSimTx = 2;
byte PinSimRx = 3;
//constructor SoftwareSerial( rxPin, txPin, inverse_logic)
#include <SoftwareSerial.h>
SoftwareSerial sim(PinSimTx, PinSimRx);//Arduino Pin 2/Rx connected to SIM Tx  
void setup(){
  Serial.println("Sending first AT command");  
  sim.println("AT"); //waiting for a single OK answer
  //sim.flush();//with or without flush()....same problem
  Serial.println("Starting loop");
void loop(){
void updateSerial(){


  while (Serial.available()){
  while (sim.available()){
    Serial.write(sim.read());//Forward what Software Serial received to Serial Port

2 lines Output ( ... waiting for some OK after AT command )
1)Sending first AT command
2)Starting loop

Any help ?
Thank you in advance.

To know Java does not mean you know Transistors
and electronics !


Oct 27, 2020, 06:01 pm Last Edit: Oct 27, 2020, 06:08 pm by jimakoskx

I HAD NOT connect the BATTERY ground cable with the ARDUINO ground

(I thought that ...... :smiley-sad: :smiley-sad: :smiley-sad: :smiley-sad: :smiley-sad: :smiley-sad:
Once i connected EXACTLY as the diagram that i my own post the image....i took the OK...
(Now i am going to learn the protocol!...finally)

Because i am coming from NOT KNOWING electronics and i am saying here as a punishment!

I am asking sorry from administrators and decide what to do with this post.

Moderators may also update
To know Java does not mean you know Transistors
and electronics !

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