[SOLVED] simcom sim900d problem(i can not write any AT Command)

why don't you try to use an oscilloscope to verify the output from the serial of your modem? rs232 is not really used by your modem, in fact its output can either be a cmos level or a ttl level, that is why I mentioned you need a ttl to rs232 converter to hook your modem to a computer, assuming you have done this already and the modem is working via the hyperterminal, then its time to test your mcu. the chip used in ttl to rs232 conversions has higher error tolerance in input than your modem, that is why it is advisable for you to grab a ttl to rs232 converter from e-gizmo, choose the model that has 2 sets of pin header for rx in and tx out.

post the setup you have done with all led's visible after power ON.....
Does it go to idle mode or switch off?????

for the cable it has really indeed a RS232 to TTL converted inside..since im using this on our other project also using a GSM module but sim500W model...
and the communication has no problem at all, i also use this cable for communicating between PIC MCU to a computer..that's why i can check if the serial function of the PIC is working well or not... on this test...PIC MCU has no problem at all. i created a short program just to send or TX some byte and the computer receives no problem...

i also use this cable in sending AT commands to the sim500W and no problem at all...
only this sim900D same setup as of the sim500w really don't work... i ordered 4 samples to test..and used 2 of it and still no good communication...

i will post some pics after i reconstruct the breadboard... thanks....

for sim900D



- Power supply is 12vdc 2A
- regulated by 7805 to convert the voltage down to 5v
- with zener and 1N4001 diode in series to get the voltage down to 3.6v
- then connected to SIM900D VBAT pin and with GND also
*now power supply for sim900D is setup and OK
- 1 LED for the NETLIGHT
- RX of sim900D is connected to the TX of DCU-11 data cable
- TX of sim900D is connected to the RX of DCU-11 data cable
- GND of DCU 11 cable is connected to the GND of sim900D
* now serial communication is setup and OK (we'v used this setup for SIM500w and sim300D and working fine)
- we connect PowerKey to the GND for 2sec and NETLIGHT LED starting to BLINK fast (since no simcard)
- supposdly we should see "RDY" "CFUN" "CPIN" and etc... to the SERIAL TERMINAL Software but we havn't (like what sim500w and sim300d does)
- we send "AT" and "ENTER", "OK" is expected but we receive garbage...
- then we try changing the baudrate but same thing happened (all baudrate available has been tested)
* now we tried the suggestion to connect RTS to CTS and DTR to DCD
- CTS Connected to RTS = Data Sent equals Data Received and mostly garbage
- CTS Connected to RTS and DTR Pulled Up = Data Sent equals Data Received and Continuous Reply of Blank Data
- CTS Connected to RTS and DTR Pulled Down = Data Sent equals Data Received
- CTS Connected to RTS and DTR Connected to DCD = No Reply

* we tried 4pcs of sim900D module and all has just same behavior.., is there any lacking method we missed?
kindly tell us what we need to do just to communicate with the module...

thanks...

can you write the LM7805's manufactturer part number excatly.

LM78L05CMX - 7805 voltage regulator part number

why u need the part number?

what is the maximum current output this reg. sometimes sim900d needs up to 2A

LM7805 max current is only 1.5A....

but sorry i forgot to tell u that now we use LM350 with adjustable voltage output using resistors and with 3A output..

---------- Post added at 15:23 ---------- Previous post was at 15:19 ----------

just posted the breadboard we'v made...
it doesn't goes to idle nor off and its hard to determine though since we can't see any data coming from the module..

if it turms off we should see "NORMAL POWER DOWN" right? but we havn't since we are in communication problem..

thakns

yes you should see normal powdown. i think there is another problem. but is there any schematic please upload here. this picture very complicated to analyze it..

schematic for sim900D, only connected to the computer using data cable (DCU-11) USB to serial TTL232 converter...

Please guys help me on the link below:

https://www.edaboard.com/threads/208134/#post882823

the baudrate changed in the hyperterminal, can't send AT+IPR to the modem due to communication problem...
and yes i only use RX,TX and GND... only tried sometimes connecting the DTR to DCD and RTS to CTS and other setups, just thinking might help..but still not...

try changing baud rates from hyperterminal side and check all... one of them should work..

homermike said:

schematic for sim900D, only connected to the computer using data cable (DCU-11) USB to serial TTL232 converter...

Click to expand...

your schematic seems okay.. i dont see any problem in you setup... where did you bought that usb to serial cable? are you sure its working as it should? hmm

problem is solved.. we use sim900 instead of sim900D...