[SOLVED] sim900 doesn't recognize the sim

[sazary]

Hi
we're trying to build a device using NXP LPC1768 as the main micro controller and SimCom SIM900 as the GSM module.
sim900 turns on and net status light starts blinking with a 64/800ms rate, which is indicating that it has not registered on the net. these are the commands we send and their responses:

AT&F
OK

AT
OK

AT+CFUN=1
OK

AT+CFUN?
+CFUN: 1
OK

AT+CPIN?
+CME ERROR: SIM not inserted

AT+CSPN?
+CME ERROR: SIM not inserted

AT+CSMINS?
+CSMINS: 1,0
OK

AT+COPS=?
+COPS: (1, "Iran Taliya","Taliya","43232"),(1,"IR-TCI","432 11","43211"),(1,"MTN Irancell","Irancell","43235"),,(0,1,4),(0,1,2)
OK

AT+COPS?
+COPS: 0
OK

AT+CREG=2
OK

AT+CREG?
+CREG: 2,0
OK

i should note that the sim card needs no PIN, has charge, and works in a functioning phone.
we are using a 1.8v sim card, and the odd thing is that when we probe pin 30 of sim900, which is SIM_VDD, we see 1.2V. i don't know where should we examine to find the problem, and your help is greatly appreciated.
thanx

 

[sazary]

problem solved by adding two big capacitors, one between VBAT and GND of sim900, and between VCC and GND of sim card holder.
also, power source of sim900 changed to a better one; although it doesn't consume more than 0.20 A current.

 

[Soumyajit]

problem solved by adding two big capacitors, one between VBAT and GND of sim900, and between VCC and GND of sim card holder.
also, power source of sim900 changed to a better one; although it doesn't consume more than 0.20 A current.

Continuous power consumption is not more than 550mA (as we have tested on field). But maximum surge current may rise upto 2 Amps for which a high value low ESR (preferably a Tantalum capacitor) capacitor is expected between VBATT & GND. VSIM & GND also required capacitor for decoupling purpose.