TC35 GSM module does not respond to "AT" command

Still the same problem.

It seems that gsmSerial.available is not true.

 if(gsm_char=='t'){
      
        gsmSerial.print("AT\r");  //Send test command
        delay(5000);
      
         if (gsmSerial.available() > 0 ){
            gsm_char = gsmSerial.read();
            Serial.println(gsm_char,DEC);
          }
    }

Although the the checking of available character is perform after 5 s, there could be possibility that the character comes in after 5 s although it's rather unlikely. In that case, you serial check will return zero.
Why not doing something simpler like this:

if (Serial.available() > 0)
{
  gsmSerial.write(Serial.read());
}

if (gsmSerial.available() > 0)
{
  Serial.write(gsmSerial.read());
}

Whatever you type on the PC should be relayed to the modem and vice versa.
If this fails, it could be something simple like inadequate current of the power supply or a GND is not connected between the boards.

Still the same problem... :~
I can not go in this part of the loop:

if (gsmSerial.available() > 0)
{
  Serial.write(gsmSerial.read());
}

Ground of the TC35 module is connected to the ground of the Arduino...

The TC35 module is powered by a adjustable power supply witch is set to 5V DC & max 1A.

On the display of the power supply i can see the current swing between 20 - 80 mA...

I did read some thread over the net, some saying it the default baud rate is 19200 bps for this modem.
Not sure whether this is true, but worth trying out?

unfortunately it does not work with 19200 bps.

Another thing to try would be shorting the CTS & RTS together.
Some modem enabled these handshake on default setting based on my experience.
Worth a try I guess.

And are you sure 1 A is enough? Usually most module out there range from 1.8 - 2.5 A (Sierra, Cinterion, SIM, uBlox).

I connected the CTS0& RTS0 to each other but i don't see a difference in the serial monitor.

Yes maybe 2A is required in some situations but now it's only using 90 mA at max ?

I had a quick look at the TC35 manual and I think you shouldn't overlook the fact that the serial interface operates at 2.65V. The Uno's serial operates at 5V. Apart from communication problems (also arising from the differences between CMOS and TTL levels), you are running the risk of damaging your GSM module. You may want to search for more information on signal conversion before returning to the software issue.

Forgot to mention this earlier.
I have a TC35 module which already has a level converter on it( MAX232E ).

This is the exact module that i bought:
http://www.ebay.com/itm/GSM-SIEMENS-TC35-SMS-Wireless-Module-UART-232-TC35I-MC35I-ge-/281035188132?pt=LH_DefaultDomain_0&hash=item416f00a7a4

drled:
Forgot to mention this earlier.
I have a TC35 module which already has a level converter on it( MAX232E ).

This is the exact module that i bought:
http://www.ebay.com/itm/GSM-SIEMENS-TC35-SMS-Wireless-Module-UART-232-TC35I-MC35I-ge-/281035188132?pt=LH_DefaultDomain_0&hash=item416f00a7a4

Good. Then how is it connected? You only said that Txd0 of the module is connected with pin 2 on the Arduino, no mention of where the tx of the Arduino (pin 3 in your code) is going. Also you talk of Txd0 and that gives me the impression you are bypassing the level converter and connect directly to the GSM module, but without manuals or schematics it's hard to tell.

This is the schematic of the module.

Right now i have 4 wire's connected to the Tc35 module:

+5V from the power supply is soldered to JP4 VCC.
Ground from the power supply is soldered to JP4 Ground.

Pin 2 arduino(SofttSerial Rx) --> Rxd0 JP6
Pin 3 arduino (SoftsSerial Tx) --> Txd0 JP6.

There's an extra wire between the ground of the arduino to the ground of the TC35.

Unless I'm missing something (which happens rather frequently, so double check yourself) all output pins on the board go into the GSM module. Your only access to the MAX232 seems to be through the serial port itself (pins 2=OUT, 3=IN, 5=GND).

I'm afraid that if you were directly connecting the RXD of the TC35i to the Arduino board, it might be damaged by now.

I am using a TC35 not a TC35 i.

@ Spatula: I don't want connect RS232 levels (+12 V?) to my arduino uno ? So i don't have to use the output pins of the max 232 ?

You are right, the other side of the converter is at RS232 levels, so it seems we are still lacking a TTL - CMOS level converter. My understanding is that connecting the Arduino pins to the JP6 pins bypasses the MAX232 and may damage the GSM module.

I went through the other documentation from the Sainsmart site but I found it less than informative, and I'm afraid that only people who dealt directly with this device can provide guidance. Here in the forum I found this Arduino Forum creative solution, where the poster created a loopback on the MAX232 and (apparently) managed to obtain the required conversion. There is no explanation, however, and the desired effect depends on having full access to the MAX232 pins and on powering it with a 3V source. I also wonder whether there's any undocumented accessory (such as the jack connectors shown in the photo) that can perform the trick.

48X24X48X:
I'm afraid that if you were directly connecting the RXD of the TC35i to the Arduino board, it might be damaged by now.

I am in the same situation, I might have killed the modem.
however, i was following this website, which says it worked to him...
http://denhart.dk/2012/01/siemens-tc35-gsm-module-arduino/
there are pictures showing the direct connections.

any idea?
y am getting the ÿ on each gsmSerial.read()
although its the same as if I disconnect the wires, so thats not saying anything good.

the led on the modem is flashing but i cant get anything usefull on the serial monitor.

any test to check if modem is burned?
its interesting to see that the led does blink constantly.

Sergegsx:

48X24X48X:
I'm afraid that if you were directly connecting the RXD of the TC35i to the Arduino board, it might be damaged by now.

I am in the same situation, I might have killed the modem.
however, i was following this website, which says it worked to him...
http://denhart.dk/2012/01/siemens-tc35-gsm-module-arduino/
there are pictures showing the direct connections.

any idea?
y am getting the ÿ on each gsmSerial.read()
although its the same as if I disconnect the wires, so thats not saying anything good.

the led on the modem is flashing but i cant get anything usefull on the serial monitor.

any test to check if modem is burned?
its interesting to see that the led does blink constantly.

I would be more optimistic: since it doesn't work, you didn't use it long enough to fry it. The post you link shows that this modem is tolerant of 5V, and this is confirmed by the experience of another member here. See this post http://arduino.cc/forum/index.php/topic,154156.0.html: the solution is a simple voltage divider.

As for the strange characters they often indicate a mismatch in baud rates. The fact you still get them when the modem is disconnected may indicate a buffered input, or maybe noise on the Arduino RX (may not be isolated, check also the back of the board). It may also be a code issue (are you reading the modem using HardwareSerial or SoftwareSerial, and on which Arduino model?). If you suspect a code issue I would advise to create a new thread with your code in it.

Anyway I would start from setting up the voltage divider before doing further tests.

so should i just use a 1K and 2,2K resistor for each line and connect it directly from the arduino to the modem pin header?

btw, just for testing purposes...if I insert the SIM card and provide 12V to the power jack + press the reset button. If i try to call the number should I get signal? I am getting that the phone is not available. This is the first step to clarify although im loosing my expectations on this modem and thinking of getting one of this...
http://www.ebay.es/itm/GSM-Modem-Wavecom-Q2303A-Module-COM-RS232-Serial-Port-AT-Commands-SMS-Voice-Call-/130832865317?pt=PCC_Modems&hash=item1e763f1825#ht_2494wt_1397

forget my questions about making the TC35 work, just got magic smoke out of the regulator and im done with trying to make it work, I will order the wavecom modem which in theory is easier to work with.