Comments on: Interfacing Arduino with a Telit GM862

By: Interfacing Arduino with a Cellular GSM Modem | EngBlaze

Interfacing Arduino with a Cellular GSM Modem | EngBlaze — Fri, 21 Oct 2011 01:03:52 +0000

[...] easy to find, easy to work with, and inexpensive. Alexander Weber’s description of how to connect a GM-862 to the Arduino’s serial bus and his sample library code are largely applicable to many cell modems. Most units still utilize [...]

By: Panos

Panos — Thu, 06 Oct 2011 15:36:22 +0000

Also, some supplementary questioning. Do I have to do something for the 2.8V levels, set up a voltage divider and pull up resistors to make the project work regarding the current hardware that I own at the moment?

I thought having the usb eval board would be easier to interract with arduino. please let me know about it. Thanks

By: Panos

Panos — Thu, 06 Oct 2011 09:46:59 +0000

Hi, there

really good job over there with code. I would like to thank you in advance. I face a small problem though. I read all the comments related to the pull up resistor on the Rx pin.

Here is what I got: Sparkfun’s USB Evaluation Board, External power supply and the USB untouched. I connect the TXD from the board to Arduino’s Tx and the RXD to Arduino’s Rx. The problem is that I cann’t read the Rx response from the gm862. What should I do?

I haven’t any voltage divider for the TXD pin. When I send commands, modem works fine.

When you say “pull up resistor for the Rx pin”, you mean just connect a 100k resistor like this?…
Rx————-/\/\/——Powermon
|
RXD——-

If it’s possible please simplify the schematic.
Thanks alot

By: NaThAN

NaThAN — Wed, 28 Sep 2011 18:11:10 +0000

I managed to make the module communicate. But the only way to test it, is by putting the RX module pin to another serial port, and the transmit from the arduino to my module TXD. Both GRN are connected to my circuit.
Now I can send a lot of commands to my module and receive the correct answer to my PC.

But because I need to make a program that handles some data that’s been received by arduino, I need it to work fully with the arduino IDE (Serial Monitor).
I am using some kind of code but sometimes I receive strange characters that are not making sense. Everytime I receive the correct answer etc.”OK” but its followed by characters.

[code]

#include

NewSoftSerial mySerial(2, 3);

void setup()
{
Serial.begin(4800);
Serial.println("GM862 testing...");

// set the data rate for the NewSoftSerial port
mySerial.begin(4800);
mySerial.println("AT");

}

void loop() // run over and over again
{

if (mySerial.available()) {
Serial.print((char)mySerial.read());
}
if (Serial.available()) {
mySerial.print((char)Serial.read());
}

}[/code]

I press the reset button each time.
What I receive to my arduino serial monitor:
[quote]GM862 testing…
EÕÔHèjªHøGM862 testing…
AT

OK
GM862 testing…
AT

OK
GM862 testing…
Q55RzµÕHøGM862 testing…
AT

OK[/quote]

I need to compare the “text” i receive from myserial to my arduino with another string.
For example, I need to know how to compare what I receive, with the word “OK’ or the word “GM862-GPS” so i make a routine for the program to do some functions if its TRUE.
So I need two things… A code that receives the data and saves it to an array, when it receives the carriage return to make the data as a string, and serila print it to myserial monitor.
The second thing is to compare it with another string. I think that’s easy by using the strncmp() function.

I am trying something like this…

if (mySerial.available() == “OK”) {
Serial.println(” Modem –> OK”);
}

Can someone help me by giving me an example code of what I want to do? Or just fix this one?

Thanks in advance!

By: Alex

Alex — Sun, 25 Sep 2011 14:14:38 +0000

@NaThAN maybe try with an Arduino Mega, which has two serial ports.

By: Alex

Alex — Sun, 25 Sep 2011 14:12:57 +0000

@jimmy, yes, you should read “OK” from the module. If sending works, but receiving doesn’t, then check the rx line again.

By: jimmy

jimmy — Fri, 23 Sep 2011 22:47:04 +0000

Hi Alex.
i recently started on this project and i need your help.
throught an arduino duelmilanove i am communicating with my gm862.i was able to send an sms to my cellphone.
the problem is that i dont have communication from the gm862 to my arduino.
if i udnerstand it all corectly when i send to the telit
Serial.print(“AT”)

i should get an OK Responce from the telit Showing up to the serial monitor right?
well i dont :/ i dont get any responce from the telit to the monitor.

By: NaThAN

NaThAN — Fri, 23 Sep 2011 17:19:15 +0000

sorry…the command i am using is: “GM862 modem(&Serial, onPin, PIN);”

By: NaThAN

NaThAN — Fri, 23 Sep 2011 17:17:51 +0000

I am using the command: “GM862 modem(&Serial3, onPin, PIN);”

By: NaThAN

NaThAN — Fri, 23 Sep 2011 17:17:01 +0000

Hi there!
I ‘ve started a project for my university on the Telit GM862 and arduino communication.

I managed to send an SMS to my phone, the GSM connects easily (5-6 seconds) but i cannot receive a response to the arduino.

I am connecting the TXD (+5V) of arduino to the TXD of the module using a voltage divider (+2.8V)
I also connect the RXD directly to my Arduino RXD.
I can send from my arduino anything but i cannot receive a thing.

I have uploaded your sketch and everytime i receive “no response” not even the RXD led on the arduino flashes.
I am using an arduino Duemilanove and i am connecting the RXD of the module to the RXD (pin 0) and the TXD to the pin 1 (TXD) of arduino, using a voltage divider.
The module should respond with “OK” if I write on the arduino serial monitor “AT” and press send, right?

Please help me, I am stuck on this for about 2 days.