interface mobile with a microcontroller problem

Hi
this is my first time to post hear i have been reading the posts and it is really very helpful
well.... i started interfacing Siemens c35 with my computer and it was working and everything was ok
just when am about to start working with the atmel microcontroller it stopped respponding to at commands..even with my pc it is not responding, tried many times to check the baud rate and everything was right but it just stoped working i don't know y
so i was starting to think about getting another mobile device so ..
if anyone please tell me if i can fix the c35
or tell me if they know a list of mobile that support the at commands other than siemns i was thinking about getting a sonyericsson like T616 couse it is available right now
so does anyone know if it will work? or any other models that work in sony ericsson?
thanx in advance
my e mail is ( [email protected] )
if u have any idea please post an answer or u could contact me directly
thanx again

may i see your circuit? probably a wrong connection. I just hope you did not burn ur phone :-s

thanx for replaying
am using a max 232 between the pc and the mobile
it was working at first and i was able to send sms with at commands but suddenly it stopped responding although the mobile it self is still working but no response to at commands i attached the max configuration that i worked with but i didn't use the auto ignition and it was working fine i don't know what happened
also am using vcc from the usb port through a cable that i made not from the serial port and was working fine
hope u could help me today i found another siemens c35 i'll get it by the end of the week so if there was something with the connection wrong please tell so i won't be doing the same mistake again
and thanx again for replaying

the thing is you need max only if you are connecting your phone with PC, but no need of max if connecting to microcontroller, just RX TX and ground.

I hope u did not use the above schematic to connect phone to controller.. did you? if thats the case, your phone should be fine only problem should be with controller it might got burnt.

no i didn't try to work on a microcontroller yet still working with the pc but it is not working anymore
if everything is right
u think i may got the Tx or Rx shorted while trying to connect it couse i didn't have the cable so i had to directly connect it to the pins and so maybe when i was trying after it worked the first time one of them got shorted with vcc and i was checking the connection while the charger was on so maybe that what happend
but everything is ok so i should try with a new one it will work fine right?
one more question
do u have an idea of any mobile sony ericsson that will work the same way couse i can't get anyone from the older models i can get a T616 if it will work with serial connection just like the C35 if u know any please tell
and thanx again for replaying

I am assuming you removed the diode and regulator from the supply line,
sorry but have to check.

There are various grades of MAX232,
the one you have may need bigger capacitors.
Try making all four caps 1.0 uF.
Place a 10.0 uF capacitor between ground and five volts.

Again you need a 'low' voltage Max232 to work with the
3 volt data signals.

Data in and Data out are 3V logic level.
19.200 bps 8,N,1

Does the USB port still supply five volt ?

yes the usb still supply me with 5 v and am already using 1.0 uF caps
it was working but suddenly stoped that's y i think that the TX and Rx lines in the mobile are the ones that have problem maybe they got shorted by me when i was tring to connect them after the first time it was working
that's y i was asking if there is something wrong with the max than maybe got them burned after a while of useing it couse it was wroking
and i was asking if there is any sonyericsson mobiles that would work the same way i can get a T616 but i want to know if it will work or not befor i buy it
thanx for replaying

and yes i know it should be 3 volts couse i already used this max converter to work on a zegbee rf modem and it was wroking fine
and the mobile also was working fine maybe it got shorted by me through a mistake but i don't remember .... :-|
if u have any suggestion about sonyericsson mobiles or maybe nokia that will work the same way with at commands that will be helpful
P.S it is really hard to get a very old mobile like nokia 6210 or t28
thanx again and sorry for bothering u

ok i just realized that the max converter that am using isn't the same schematics as the one i posted earlier this one actually i got it from a friend while working with him on the zegbee
i'll post the new one but sorry for bad drawing
by the way the mobile was working with the one am using before and then it stoped responding to at commands
is there something wrong with this one am useing??
thanx again and sorry for bothering

sorry forgot the GND