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Author Topic: TC35 GSM module does not respond to "AT" command  (Read 3783 times)
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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).
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I'm afraid that if you were directly connecting the RXD of the TC35i to the Arduino board, it might be damaged by now.
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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 ?

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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 http://arduino.cc/forum/index.php?topic=56628.0 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.
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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.
« Last Edit: March 25, 2013, 06:06:46 pm by Sergegsx » Logged

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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.
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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
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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.
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