try changing the line to:

Serial2.printf("AT+CSTT=\"%s\",\"%s\",\"%s\"\r\n", apn, user, pass);

Thanks
Felix

I'm trying your code but Arduino doesn't compile with this error:

Compilation error: 's' was not declared in this scope

about this line:

Serial2.printf("AT+CSTT="%s","%s","%s"\r\n", apn, user, pass);

no way to work with SIM800L MODULE!!

tips??

https://github.com/vshymanskyy/TinyGSM

in the example sketches simply change serial1 to serial2

:D

not all is necessary, but maybe helpful …

what I have learned up to now:

• it works with HardwareSerial; no libraries to declare; default pins

• I can make phone calls

• I can send and receive SMS

• the audio of the phone is not connected to the M5Stack; it's just the bare minimum.

• if required, I might connect a better antenna - there is a connector on the SIM800L module and a hole in the base module I could use.

• no soldering, no cables, no voltage problems

• no EDGE, no LTE

• the LED on the SIM800L module can be seen through the headphone hole.

• the Arduino IDE installation brings a GSM library, but it is not listed under examples in the IDE.

bye for now
Walter

HardwareSerial Serial2(2);

void setup() {

M5.begin();
M5.Lcd.printf("GSM Test"); // just to see that the program has started
Serial.begin(115200); // switch on the serial "terminal" of Arduino IDE

// Serial2.begin(unsigned long baud, uint32_t config, int8_t rxPin, int8_t txPin, bool invert)
Serial2.begin(9600, SERIAL_8N1, 16, 17); // 9600 baud seems to be the default for modems; pins as printed on the PCB board
at("", 200);
at("Z", 200); // reset all parameters to the user defined profile
at("I", 200); // display product info
at("+CPIN?", 200); // unlocked ?
at("+CGREG?", 200); // check the registration status of the device
at("+COPS?", 2000); // get operator
at("+CSQ", 200); // check signal quality
at("+CNUM?", 200); // find phone number of the device
at("+CNUM", 2000); // find phone number of the device
at("+ATS0=3", 200); // answer incoming calls after 1 ring tone(s)
at("+CREG=1", 200);
at("+CREG?", 200);
at("+CFUN=?", 200); // list functionality levels
at("+CFUN=1", 200); // set to full functionality
// at("+COPS=1,0,"E-Plus"", 200);
at("+CR=?", 200); // service reporting control
at("+CGATT=?", 200);
at("+CGATT=1", 200);
Serial2.printf("AT+CSTT="%s","%s","%s"\r\n", apn, user, pass);
delay(200);
Serial.print(Serial2.readString());
at("+ICCID", 200);
at("+GSN", 200);
at("+CIICR", 200);
at("+CIFSR", 200);
at("+CPOL?", 200);
at("+COPS=?", 2000); // get operators
}

void at(char* sCmd, unsigned long lDelay) {
Serial2.printf("AT%s\r\n", sCmd);
delay(lDelay);
Serial.print(Serial2.readString());
}

// now that the intro is done, we go into an interactive loop, where we can enter AT commands or press a button to do something
void loop() {

if(Serial.available()) {
int ch = Serial.read();
Serial2.write(ch);
M5.Lcd.write(ch);
}

if(Serial2.available()) {
int ch = Serial2.read();
Serial.write(ch);
}
if (M5.BtnA.wasPressed()) {
M5.Lcd.printf("\nhangup");
at("H", 200); // hangup
}
if (M5.BtnB.wasPressed()) {
M5.Lcd.printf("\ndialing");
at("L8", 200); // volume 0-9
at("D0043xxxxxxxx;", 2000); // dial
}
if (M5.BtnC.wasPressed()) {
M5.Lcd.printf("\nsms");
at("+CMGF=1", 200); // set the GSM Module to text mode
at("+CMGS="+43xxxxxxxxxx"\rTest SMS by Walter\x1A", 2000); // sms
}
M5.update();
}

Now the AT commands work ...

Br
Jp

any update of demonstration source code for the sim module with realtime streaming audio over Gsm ?

Looking for using it as a basic talking only smartphone in full duplex, send and receive at the same time ?
If possible Under Arduino IDE , with ino file ...
Good project and information..
...
Great day.
Jp

Is the mic on GPIO5

No. mic and headphone are connected direct to SIM800L module.
GPIO5 is reset.

Interconnection
M5 Stask <> SIM800L
Vbat - Vcc (3.7-4.3V)
GPIO16(RX) - TXD
GPIO17(TX) - RXD (must be not direct 3.3V > 2.5V)
GPIO5 - RST
GND - GND

RING is not used.
DTR is not used.

MIC+, MIC- to microphone.
SPK+, SPK- to headphone.

Example for Arduino

HardwareSerial SIM800 (2); // pin 16 = RX, pin 17 = TX
for example
https://yadi.sk/d/SxWs6t0x3UBco6

Not sure where you purchased yours but they should have included the photo below outlining the pin-outs used.

Here is a link to a manual for the AT command set for this sim module:
https://cdn-shop.adafruit.com/datasheets/sim800_series_at_command_manual_v1.01.pdf

There are many more datasheets at the Simcom website link if you are prepared to register:
http://simcomm2m.com/En/module/detail.aspx?id=138

Here is a link to a simple program that could form the basis for use with the M5 stack.... You can probably find more examples on github.
http://www.ayomaonline.com/programming/quickstart-sim800-sim800l-with-arduino/

It will need some conversion to make it compatible with the M5Stack. For starters you would need to add this to the start:

#include <M5Stack.h>

The GSM format used on this module is not supported in my country so I have no experience using it.

Good luck.