hello, i have a problem with the tx pin in the gprs module, it is the second time that i have the same problem. I connect the module with my own circuit, it works perfectly, but suddenly, the tx pin stops working, it also happens in the microprocessor tx pin, what can be the problem?
Thanks. Regards
Make sure that the TX pin from the gprs is an output driving into the RX pin of the micro which is an input.
Depending on if the equipment is defined as DTE or DCE a TX may be an input or an output. The same goes for RX.
You always need to connect an input to an output. It sounds like you are connecting two outputs together and frying something.
is it possible that the tx pin is defined as input? I am sure that in my procesor tx is an output an rx is an input, because i programed it. how is it defined? is it an DTE or a DCE?
Can i connect both in some way?
Thanks.
Regards
If your TX pin is an input then there is no harm in connecting inputs together, It is connecting outputs together that kills things.
Also check what voltage you have on the pins. Are they full RS232 voltages are you expecting TTL voltages or even 3.3V? A way of killing an input is to put too much voltage in it.
Simply saying "the gprs module" is not too helpful in knowing what you actually have.
Can i connect both in some way?
Not at the same time ALWAYS connect an input to an output and always connect the right voltage output to an input. Please find out what you have and what it expects.
no, TX pin is an output in my microprocesor.
The voltage is correct, both are from 0 to 3.3 V and the problem is with the outputs (or what i think that are outputs)
This is what i have:
http://www.libelium.com/squidbee/index.php?title=New_GPRS_module_for_Arduino_(Hilo_-_Sagem)
In this tutorial they say that if you connect the module to the computer, you have to change two jumpers, so, i suposse that the problem is what you say about DTE and DCE, but i don't understand very well the diference.
Thanks! Regards
Can you state the problem again, what are you connecting to what.
From the schematic jumper JP2 and JP3 swap the TX and RX over if this is not right then you will have problems.
I put the jumpers in "arduino" position, and i connect the TX pin in arduino GPRS to the RX pin in my microprocesor, and the RX pin in arduino GPRS to the TX pin in my microprocesor.
The problem is with both TX pins.
I was looking for information about inputs and outputs and they are configurated as i though, in both devices TX is an output and RX an input, so, i connected an input with an output.
Thanks. Regards
when you say:-
my microprocesor.
What exactly do you mean? is it your PC (or Mac) or is it the Arduino or is it some other microprocessor?
it is another microprocesor.
But what voltage it it running at. 3V3 or 5V, you could have a miss match.
no, both of them are 3.3v
Sorry I can't think of anything else that is destroying your pins except connecting outputs together.
Next time connect them up through a 220R resistor just in case, it can't do any harm.
i am without any ideas also. But thank you for your interest.
Regards!
Also check what voltage you have on the pins. Are they full RS232 voltages are you expecting TTL voltages or even 3.3V? A way of killing an input is to put too much voltage in it.
Mike I found that my dryer has a serial connection (it's written on the service manual) between the user interface moule and the main control module.
I suppose if I catch data transmitted through the UI module and do a little reverse engineering, I could make it an Arduino-powered dryer...
Is it enough to measure voltages with the tester?
I suppose in these cases it's commonly used RS232 driver like the MAX232 right?
I found this demo board uses I2C...
http://www.st.com/stonline/products/literature/bd/15217.pdf
I could make it an Arduino-powered dryer.
Well controlled rather than powered. 
Is it enough to measure voltages with the tester?
Well an oscilloscope is better but if you have it with nothing going on and you measure a -ve voltage it is probably safe enough to assume it is RS232 and so you will need a MAX chip.
Demo board is interesting, but will you be able to get one. Companies like ST often subsidise boards like this ans some times won't sell them to individuals.
Hehe yeah you're right, it would be controlled
There are five wires between the modules. Pin 1-2 are the data bus. When it's idle the voltage is fluctuating between 0.16V to 0.06V. When pressing buttons the max voltage I measured is 2.48V.
The pin 3-4 are the power supply (+5.1V steady) and the pin 5 I suppose it isn't connected.
Is it right to use the MAX3232, a 3.0 to 5.0V driver?
Any advice to avoid frying the dryer electronics? 
I'll use the 220R resistors too....
When it's idle the voltage is fluctuating between 0.16V to 0.06V.
That doesn't sound like a TTL serial line, they should sit high when idle. So it is either not a serial line or in needs it's logic inverting first.
it works as my GPRS module, you have to put a tension divisor before the input in your module. At the output it is not necesary because the threshold in the receptor is less than 2.48 V.
I am not sure if i explained (my english isnt good)
Regards
I thought about it and i didn't do a correct reading with the tester... Now I measured each of the RX and TX lines and the GND pin, and discovered that in idle they are both +5.1V when idle and sinks to about 2.4V when pressing buttons.
So is it a real TTL signal that Arduino can read without other hardware right? Can I read the TTL signals from the PC through the Arduino? Otherwise I'll buy the MAX232, cause I think it's easier to do reverse engineering through a PC