Problem with receiving strings from SIM900 with INT_RDA

[Mustang1945]

ezflyr... i am not trying to get "something" to work, i have been searching for documentation of the board and it doesn't exist.

[temtronic]

if this...
Sorry, i have been busy in my job, here is the website and the pictures there are better than mine:
http://www.sainsmart.com/sim900-gprs-gsm-board-quad-band-module-kit-for-arduino-high-quality-new.html...

is the board you are working with, it does use a MAX232 to interface, making it an 'RS232' type device.
To make it interface to your PIC you WILL need to add another MAX232(or equal) between the PIC and the 'modem'. Be sure to put rx to tx, and tx to rx AND a gnd !
Providing you have the serial config correct (baud,bits,etc.) it 'should' work....

Jay

[Mustang1945]

Thanks for the idea but i tried that configuration and i used getc, and it works, then i programmed the PIC to use get string and didn't work, it is the same error.

I send the sms, the program goes to the interrupt, turns on the led that indicates that I have received the correct word and stays there...never returns to main program.

[Mustang1945]

hi...look at this

https://s3-ap-northeast-1.amazonaws.com/sain-amzn/20/20-012-106/SIM900_A_+Module+Series+Debug+_unfinished_.pdf

this is the board i am using but if you read, they say that hardware conection with PIC is >

TX PIC...TX SIM900

RX PIC...RX SIM900

that is wrong...

i connect tx with rxsim900 and rx with txsim900 and it works.

and in the rs232 interface they say that >

TX (rs232-usb interface)...RX SIM900(rs232 interface)

RX (rs232-usb interface)...TX SIM900(rs232 interface)

in this case the connection should work but in the sim900 rs232 interface the pins are changed, i use an rs232-usb interface and the connection works with this configuration>

TX(rs232-usb interface) ...TX SIM900 (rs232 interface)

RX(rs232-usb interface)...RX SIM900 (rs232 interface)

i think i have bought the worst sim900 board , no exists documentation, and when i found something...it is wrong

[ezflyr]

Hi Mustang1945,

A colleague at work recently asked me to help him build a remote temperature monitor for his vacation house. I think a GSM solution would be ideal, so I decided that this would be a good opportunity to (1) help him, and (2) help you! So, I ordered one of these Sainsmart GSM modules from Amazon for this project. Once I receive it, I will figure out the necessary connections between the Sainsmart module and the PIC, and will document my findings and post them here. I will also document a level translation circuit using commonly available components. In this way, I can help my colleague and you at the same time. Win-win!

We are about to celebrate the Thanksgiving holidays here in the US, and I will be traveling a bit. I'm not sure when the Sainsmart module will actually arrive, so it may be as late as mid-December before I can post my findings, but I promise to do so at my earliest convenience.
_________________
John

If it's worth doing, it's worth doing in real hardware!

[Mustang1945]

ezflyr...thanks

i will find some time to continue doing tests with get string, as i said... i am late with my proyect, meanwhile... i will continue using getc

[ezflyr]

Hi,

If you think you are actually receiving valid serial data from the GSM board then you should post some 'problem code' for us to take a look at! All my projects use the int_rda serial interrupt and the getc() functon, and I generally avoid gets() like the plague! Sometimes I implement a linear receive buffer, and sometimes I implement a circular receive buffer, depending on the data throughput.
_________________
John

If it's worth doing, it's worth doing in real hardware!

[ckielstra]

I had a quick look at all the posted links and documents.
Please note that the board has both an RS232 level output and also a TTL level output. Perhaps this is where a lot of confusion comes from?

The TTL-level Rx and Tx signals from the modem are routed to the 3 jumpers on the board, this is your TTL-connector when the jumpers are removed. With the jumpers present the signals continue to a MAX232 and then to the larger connector, this is the RS232 level voltages.

So, to use this modem with your PIC you don't need a MAX232. Just remove the 3 jumpers and connect your PIC there. I didn't check, but most likely a 3.3V to 5V conversion is to be added.

The getstring function is a bit difficult to use. When I remember correctly, it waits for a CR but many applications send CR/LF. This LF character becomes then the first character of your next line. You don't want this as it messes up the received text.

Have a look in the Code Library part of this forum. Several GPRS modem programs have been posted there. Study them and learn.

[Mustang1945]

hi...ckielstra....sure...i know that i have 2 kinds of serial pins on the board... but you said that if i remove the 3 jumpers there is my ttl connections...but in the last pdf i posted clearly say that the 3 jumpers marked as t900,r900 and gnd are rs232 signals,no ttl.

ttl signals are near the 5v and gnd pins.

[ezflyr]

[Mustang1945]

SOLVED!!!

Hi all!!!... finally i have solved the problem:

I must use ATE0 command!

I had read about ATE command, and in some forums they had this problem when they sent a sms from the sim900 and in the mobile received the AT command, like:

[ezflyr]

Hi Mustang1945,

I sure hate to rain on your parade, but you really didn't *solve* anything, all you did was to put a band-aid on some flawed code that happened to make this work for the moment.....

Here is what I mean. You said: "somehow the sim900 sends unnecessary data to PIC when you are getting the string and keeps the PIC in the INT_RDA". From this statement, I assume that you are doing something like this:

[Mustang1945]