Car tracker using GPS and GSM with one hardware USART chip

ezflyr · Joined: 25 Oct 2010 Posts: 1019 Location: Tewksbury, MA

It's kind of late in the process to be telling us that your modem is equipped with an interface board isn't it??

If the module is fitted with a MAX232 then you'll also need one fitted to your PIC UART in order to successfully communicate between the two.

John

princejude · Joined: 07 Aug 2010 Posts: 72

ezflyr · Joined: 25 Oct 2010 Posts: 1019 Location: Tewksbury, MA

Hi,

Do you have a data sheet for the hardware you are actually using?

You generally cannot connect your PIC directly to the Rx/Tx pins of another device if there is a MAX232 already connected to that device. Can the TC35 be separated from the interface board?

It's been over a month since your 1st post on this project, and you are still mired in the most basic hardware interface issues. This trajectory does not bode well for the successful completion of your project. I think you need to seriously step back, evaluate what you've got, and formulate a logical plan forward. If not, I fear this project is doomed. Sorry.....

John

princejude · Joined: 07 Aug 2010 Posts: 72

princejude · Joined: 07 Aug 2010 Posts: 72

Gabriel · Joined: 03 Aug 2009 Posts: 1074 Location: Panama

you dont have the datasheet....
_________________
CCS PCM 5.078 & CCS PCH 5.093

princejude · Joined: 07 Aug 2010 Posts: 72

Gabriel · Joined: 03 Aug 2009 Posts: 1074 Location: Panama

Almost all RS232 devices have or should have flow control, specially modems...
(i understand this is a very general statement)

however, most of the time tinkerers and people doing simple tasks choose to not use flow control because its simpler in hardware and software...

you do not need to disable flow control in your PIC... you dont have any. (unless you code it manually)
you must ensure that your CELL MODULE has flow control disabled.

as i have explained in several other GSM related threads, the first thing you must do is have a 100% working serial comm.

for that, i suggest you make a _Small_ program which _only_ sends "AT" command to the Cell and checks for the OK reply.

once you have that.. you have eliminated hardware problems...and you can proceed with your project with reliable hardware...

one of the main issues ive noticed while working with GSM modules (and explained in this forum several times as well) is that you need to swap your TX/RX lines ... DCE/DTE issue...

see this thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=48385

and see my second to last comment on this thread:
http://www.ccsinfo.com/forum/viewtopic.php?t=42527

lastly, the best place to start is with a terminal window, and _manually_ send the commands you want and _see_ what are the actual responses from the cell module and code your PIC based on that.

G.
_________________
CCS PCM 5.078 & CCS PCH 5.093

ezflyr · Joined: 25 Oct 2010 Posts: 1019 Location: Tewksbury, MA

Hi princejude,

Without a datasheet, you are really wasting your time, and all our time as well! Frankly, this late revelation is really an abuse of the good-will of all the people that have jumped in to try to help you with this project. If you were prepared to do this project "in the blind", I think it would have been reasonable to let us all know that from the outset...... I believe, as you apparently do, that you would have received a lot less help!

I spent a bit of time this morning looking at various combinations of 'TC35 Modem' and 'TC35 Interface Board' using Google, and got a number of hits, including from suppliers in China. I saw only 2 or 3 different board configurations that kept coming up again, and again, so it's possible that yours is one of them? First of all, if someone went to the trouble of making the hardware you have, then a datasheet does exist somewhere. Did you bother to write your source for the hardware to obtain the documentation, or did you perform your own search? Perhaps you are really inexperienced in this area of hardware design, but NO serious hardware designer would EVER embark on a project like you are attempting without FULL documentation! I suppose that you purchased this modem from China due to cost, right? Well, you are learning an expensive lesson now that cost may not be the only thing to be concerned about!

In the absence of any documentation, and given that the board works with a PC and Hyperterminal, I re-iterate my earlier suggestion to just add a MAX232 to the PIC, and get on with life.

John

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

The TC35 is an old famous modem from Siemens, now Cinterion. Depending on the housing it was sold under different names, I think the bare bones pcb was called MC35 (from module) and the one in a plastic case was the TC35 (from Terminal).
Difference between the TC35T and TC35i is that the 'i' is newer and has more commands.

What I understand from your posts is that you have the pcb-version mounted on some kind of interface board from unknown brand. Could you post a photo of your modem? And/or post a link to the website where you bought the modem.

Datasheets for the MC35/TC35 are available for download everywhere, but let's first confirm we are really talking about the Siemens modem.

The other thing is your direct connection from the TC35 to the PIC. Bypassing the MAX232 seems like a valid option so you don't have to add an extra MAX2232 to the PIC, except.... The TC35 is running at a low voltage like 2.7V (you'll have to check). If your PIC is running at 5V this is not going to work. You could add voltage level translation hardware, but much easier and more reliable is to have your PIC run at the same voltage level as the modem. Your PIC16F887 can run from these low voltages, just make sure the clock frequency is not too high (max 10MHz).

princejude · Joined: 07 Aug 2010 Posts: 72

princejude · Joined: 07 Aug 2010 Posts: 72

The front view is here : http://tinypic.com/r/jq6fb5/6
The back view is here : http://tinypic.com/r/2mceuy9/6

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

All right, so we now have confirmed it is a Siemens TC35 module mounted on some unspecified interface board.
I don't see extra specifying texts on the module so I assume it is the older type and not the newer TC35i.

Looking at your photos the interface boards should be just a power supply and MAX232 circuit. Even without a datasheet for the interface board you should be able to get the modem connected.

Next step is to confirm you made a valid hardware connection to the PIC. Up to this point you have been very vague about that. Some suggestions were given to you but you have never described your actual connection in detail. Please provide more details.

ezflyr · Joined: 25 Oct 2010 Posts: 1019 Location: Tewksbury, MA

ckielstra,

You are a better man than me. I've concluded that princejude is hopeless, and that this thread is a colossal waste of time. For whatever reason, princejude doesn't even seem to be able to help himself. He withholds critical information (that he has no documentation, that his TC35 modem has an interface board), and he completely ignores direct questions, such as the source of the board he's working with.

This forum is primarily about issues related to the CCS compiler, but a lot of general engineering technique/information is exchanged here as well. The forum is a fantastic resource, but princejude seems either unwilling or unable to be helped here. I hope you have better luck!

John