[SOLVED] SIM interfacing with SIM900D.

[yousafzai82]

Please help me.. I want to interface sim card with SIM900D. But i am not getting the voltage at the pin SIM_VDD, SIM_DATA or any other pin dedicated in the module for SIM card. Although AT commands are working properly...

 

[ckshivaram]

modem will respond to basic at commands without SIM card also....

try AT+CPIN? and see the result.. if it gives error then sim is not detected... it it sives response then its working.........

 

[yousafzai82]

Thank you for your reply...

I agree that basic commands should work but my question was that pin SIM_VDD on SIM900D should have some voltage for SIM card as it is Output pin. The circuit diagram in its manual do not suggest any external supply for SIM Card. Do i need to supply that from some external source to the SIM card??

---------- Post added at 11:54 ---------- Previous post was at 11:53 ----------

Pin SIM_VDD has zero volts although basic AT commands are working.

 

[ckshivaram]

as i told ,,, sim is not required for executing basic commands... but you need sim only if you do network related command... and sim operates at 3.3V so this voltage should appear at sim pins...

 

[yousafzai82]

Thanks once again...

As there is no voltage on pin 9 i.e SIM_VDD of the module. Is this means the module is faulty or i need to do some configuration or setting through AT commands to get this voltage on this pin..


Another option is that i need to supply this voltage externally.i.e not from the module..

 

[ckshivaram]

please give external voltage to the module and try... there is nothing you can do with at commands till SIM card is detected by modem... what is the power supply you are using???????????

 

[yousafzai82]

Thank you for your time....

I am using MIC29302 with its output voltage 3.81V for SIM900D. I am not supplying this voltage to SIM card...

---------- Post added at 12:33 ---------- Previous post was at 12:32 ----------

should i increase this supply to 4.1V or 4.2V??

 

[ckshivaram]

feed 3V or 3.3 V to sim card...... then it should solve all your problem...................

 

[yousafzai82]

i have fed 3.3V into sim card and provided a 4.7K pull up to data IO pin. But it didnt solved my problem. After providing 4.7K pull up i got the voltage at pin SIM_VDD but still AT+CPIN? is not working...ie SIM is not responding.....

 

[ckshivaram]

can you post me a picture of the modem along with the regulator on it.... i can make out something of it....

 

[yousafzai82]

Please check the image attached for SIM interfacing. I am not using SMF05C for ESD protection. Basic AT commands like ADCs, GPIOs, AT+CMGF and many more are working properly. It is not detecting the SIM card. I am not getting any voltage on pin SIM_VDD.

 

[ckshivaram]

check if your SIM card pins are not shorted with eacd other and check if the module and tthe sim holder are connected properly using multimeter...

all peripherals are independent of SIM so all those commands will work except network related... there is some problem in the hardware..... if you get the voltage at SIM caard holder your problem is solved

 

[yousafzai82]

Please comment on "ALL PINS RESET AS OUTPUT DRIVING LOW".

you can see it in the image below describing SIM interface with SIM900D in its manual.

 

[ckshivaram]

do you get the output of regulator as 3V and does this appear on the simVDD pin?

fiorst check if the 3V regulator output is connected to simVDD pin.. if yes then check the voltage at the regulator output. see if it measures 3V or 1.8V
then check at the simVDD pin and see if you get same voltage on that pin.... then insert the sim and check if the same voltage is seen.....

 

[yousafzai82]

do you get the output of regulator as 3V and does this appear on the simVDD pin?

Ans: I am not getting any voltage at pin simVDD. I isolated it from the circuit but still no voltage. Voltage levels on all other pins are usual. I think the module is falulty.

 

[ckshivaram]

replace the regulator, or lift the output pin and feed external voltage to regulator input.. and measure the output if the regulator is working or not..... check if the track is connected... check if there is a zener diode and there is voltage on any one side of diode.......

 

[yousafzai82]

Thanks...

Now i would like to explain it in detail. Maybe it will make you understand where i got it wrong.

1- I only grounded five ground pins out of 9.
2- I supplied 3.81V to VBAT through MIC29302.
3- Some AT commands were working properlyand voltage levels at all pins were normal but i didnt get any voltage on SIM_DATA, SIM_VDD, SIM_RESET, SIM_CLK when they were OPEN or CONNECTED as suggested in the manual.
4- I am making it on by grounding PWRKEY with a wire .i.e i am not supplying the pulse with MCU.
5- I am not getting RDY on Hyperterminal but i am receiving "IIII" when i ground PWRKEY with an external wire.
6- I got another SIM900D but the same problem with this module as well.
7- I have not connected SMF05C for ESD protection.

---------- Post added at 07:15 ---------- Previous post was at 07:00 ----------

8- When i shut it down by grounding it with a wire, i am getting "NORMAL SHUT DOWN"

---------- Post added at 07:29 ---------- Previous post was at 07:15 ----------

Is my module is in Charge Only Mode, in which few of the AT commands are working properly?

 

[ckshivaram]

can you post the picture of the hardware setup along with the excat circuit you ae using... i want to see the regulator and other components in the picture...

 

[yousafzai82]

---------- Post added at 10:19 ---------- Previous post was at 10:11 ----------

 

[GSM Man]

Are you looking at the SIM_VDD pin with an oscilliscope? If you do, when the module is first poowered up, you should see it breifly go to 1.8V and then to 3.3V. If it does this and then goes to zero volts it's an indication that the internal SIM power supply is not sensing the SIM card.

I've often found that the cap on the SIM_VDD line needs to be larger than recommended by the datasheet. Try using a .1 uf cap there.

I do not recommend using an external supply for the SIM_VDD line.