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Interfacing TC35i Problem

Sharagim

New Member
Hi,
I am trying to interface a tc35i gsm module .
As datasheet I connected:
1-5 -> BAT+
6-10 -> GND
18(RXD0) -> max232 (12-R1Out)
19(TXD0) -> max232 (11-T1IN)
and IGT to a circuit which trying to turn on the tc35i.

But I cant get anything hyper terminal.
When I set baud rate on hyper terminal to 115200 I and when I type I see something which is not correct for example when I type A I see H as echo.
I would appreciate if you can help me.
 

Diver300

Well-Known Member
Cut the baud rate down. Use an oscilloscope to see what is going on.

I assume that you have pins 13 and 14 of the RS232 connected to the PC.

If you remove the TC35i, and link 11 and 12 on the RS232 you should see echo on hyper terminal, and not if you don't link 11 and 12. That has to be working before you connect the TC35i.

I don't know if the TC35i echos its commands, but it should respond to AT<ret>
 

Sharagim

New Member
Thanks for your reply.
I did what you said and got echo on pc (link 11,12).
again I link TC35i and turn on the GSM and nothing happen.
Even I am not sure if it is turned on or not as there isnt any LED or ... to show me that !!!
 

Diver300

Well-Known Member
Can you monitor the current to see if it turns on? Also, if you have an old radio that can hear the GSM pulses, you should be able to hear it registering onto a network, about 20 seconds after it turns on.
 

Sharagim

New Member
Thanks again for your help.
the previous problem was a problem with current and when I tested the board find out which the current is not ok for turning on the module, I fixed that issue.
I plugged a LED on SYNC pin so I can see what is happening now.
Now I have another issue :
When there is no SIM card I can send AT command and ... but when I input SIM card I see LED blink 4-5 times and turn off , during this blinking I can send AT commands (which is about 3-4 Seconds) then stopped.
 

ikalogic

Member
i worked on a TC35i module a couple of years ago. I know there is an "ON" signal that you have to drive to turn the module on or off. i had that same issue, i think your module is turned off. You can find this signal - as far as i remember - on an RJ connector to the side of the module.
 

Sharagim

New Member
Hello,
I think you mean IGT signal!!!
After I turn on power I send a signal (low level) to pin IGT and then the TC35i seems to start working as I see LED start blinking.
But After a few seconds it is going off again . Please pay attention when I remove SIM card I dont have this problem and the LED blinking continuously.
 

ikalogic

Member
Hello,
I think you mean IGT signal!!!
After I turn on power I send a signal (low level) to pin IGT and then the TC35i seems to start working as I see LED start blinking.
But After a few seconds it is going off again . Please pay attention when I remove SIM card I dont have this problem and the LED blinking continuously.

Yes.. Yes.. it's IGT, i remember now! i told you it have been years ;)

hmm.. strange thing with the SIM.. but still on the IGT signal, do you keed it low all the time, or just give a low pulse?

I still have the TC35i module at work by the way.. i just have to find it! lol .. i could take a look and see how it behaves on my side
 

Sharagim

New Member
Hi,
Thanks for your reply.
I am sending one low pulse but I tested with some other IGT signals too which I found on the net (Maybe I am wrong on making it).
Could you please kindly check your circuit and give me more information.

Thank you in advance
 

Sharagim

New Member
Hi again ,
an update for this issue:
as I mention before I have a few second before automatic shutdown.
I tried to send some AT command to see if it can see the SIM card and it is ok , I got SIM ID with "AT^SCID" to.
So it seems SIM connection is ok too. but yet I have this issue and I must note that there isn't any alert in hyper terminal too only shutdown.

Thx
 

Diver300

Well-Known Member
Your power supply can't supply the current that the module takes.

The module, like all GSM modules, takes 1.9 A peak for 580 µs, every 4.8 ms when transmitting.

When there is no SIM, the module does not transmit, and it never finds out that the power supply is weak. When there is a SIM, the module finds a network, and tries to register. As it does so, the power supply dips, and the module turns itself off.

I have had this happen before. I am sorry that I didn't realise what the problem is earlier from your description.

You need a 2 A power supply, or a Li-Ion battery, or a capacitor of about 10,000 µF and a 0.5 A power supply.

What are you using at the moment?
 

Diver300

Well-Known Member
Have you got any capacitors near the BATT+ connection? I use a couple of 100 uF tantalums.

How have you connected the module to the power supply?

The symptoms of working unless a SIM card is in, and turning off after a few seconds with a SIM present, point strongly to weak power supply.
 

Sharagim

New Member
Thanks a lot for your helps.
I put a capacitor and problem solved. but really it is a question for me yet why the power supply couldn't support sufficient current as it is 3A.
 

Diver300

Well-Known Member
How big is the capacitor? How is the phone module connected to the power supply?

The 1.9 A pulses start and end very quickly. Even quite a short wire from the power supply to the phone module will have significant inductance. The power supply can support sufficient current, but the current cannot change from just about nothing to 1.9 A extremely quickly.
 

Sharagim

New Member
Hi,
for Test I placed a 6800 uf but I will change to lower one as it is very big. I am placing GSM module on a vera board maybe my wiring is not stable enough and I am going to change wiring structure to lower make them shorter.
With your description , Now it is clear for me why the power supply cant match the current.
Thank you very much for your help, you solved my problem.
 

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