Problem with SIM_VDD pin of SIM900B as it is always 0

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ThiVu

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Anyone help me?
The SIM_VDD pin of my SIM900B is alway = 0 when insert or not insert SIM Card.
The cap from VCC (of SIM Card) to ground is 220nF.
The cap from SIM_IO (of SIM Card) to ground is 10pF.
And VBat = 4.6V.
Because SIM_VDD = 0 , I dont detect SIMCard..
What can i do to solve it?

Thanks.
 

This is what I have receive when:
//send "AT\r"
OK

//send "AT+IPR=115200\r"
OK

//send "AT+CFUN?\r"
+CFUN: 1

OK

//send "AT+CSDT=1\r"
OK

//send"AT+CPIN?\r"
+CME ERROR: SIM not inserted

//send "AT+CREG?\r"
+CREG: 0,0

OK

//send "AT+CSQ\r"
+CSQ: 22,0

OK

Problem is although I insert various of sim cards and sim900b but it CPIN? still respond "SIM not inserted"...
 
Last edited:

I dont know why but I removed the SMF05 and modem detected SIM card.
I use multimeter and find out one of diodes is damaged. I have not replaced it by new one but everything seem to be ok.
- So What does SMF05 used to??
- And another problem, when I send some command (ex: "AT+CMGR=1\r", "AT+GSV", "AT&V") , the modem does not respond anything.
 

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