[SOLVED] SIM900D shuts down only when simcard is inserted?

Hi,
I'm working on a breakout pcb for the SIMCOM SIM900D GSM IC. It's a basic breakout with the decoupling caps, TVS and simcard holder (with corresponding resistors per the datasheet) populated on the board and is being powered by an external power supply. Without the simcard inserted (prepaid T-Mobile in the USA) the unit powers up and I can issue AT commands with no problems and perform other functions.

When I put the simcard in the unit powers up, recognizes the simcard as being installed and then about 8 seconds later automatically powers down. I can't for the life of figure out why it's shutting off. I checked for proper voltage at the Vdd pin on the simcard, put a scope on it and saw a clean clock signal and also a lot of data transfer on the IO pin. One thing I must say is that the simcard is expired, however, it works fine in another breakout pcb that I have that uses a Telit GE865. I've sent SIMCOM an email asking if they have any recommendations but I have not heard back yet.

I'm going to desolder the simcard and wire up another externally to see if it's a pcb problem but I don't think it is. I'm also wondering if it has anything to do with certification in the USA. I see the SIM900 has been certified and accepted on the AT&T network but there is no info available on the SIM900D.

Any advice or recommendations on how to troubleshoot this problem further would be greatly appreciated. Thanks.

Hi Friend,
I am trying to connect SIM900 with computer and for this I am using RX and TX connection with my serial port. Is there any other wire I need to be ground? As using only RX AND TX I am unable to connect Sim900 with the computer by using hyperterminal... can you pls tell me which wire of module I need to Ground to run module on hyper terminal by using serial interface.

thanks
Ali

My advice is for your problem:

1- Make sure you are using Shielded SIM Card Holder!
2- Desing PCB with "no trace" under SIM Card holder that trace carries signals not involved for SIM Card!

Especially under SIM Holder, no trace might be a good choice!

Good luck...

Thanks for the advice. Not sure what happened but I powered it up again a little while ago and now it works. I removed the wires several times and rewired the connections along with removing the Simcard several times and each time it powered up with no problems. Weird!!! I'm guessing I had something wired wrong the first time. Thanks again for the advice.

Hi All,
Can someone help me and provide me EVB PCB design for SIM900 ? Friends really I need this and I would appreciate if someone can provide me this PCB desing.

Regards,
Ali Ahmad

Problem solved. Looks like it was a power supply problem all along. The current burst when trying to register to the network was causing the voltage to drop just a little too much and shutting it down. It's amazing the difference of 4.0 and 4.1 on a power supply will make...LOL.