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27th December 2016, 07:15 #1
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No voltage at SIM VDD. SIM card not inserted error in SIM900
I have a SIM900 pcb where there is SIM Card holder. Attached is its schematic.
All the components (res,cap.) are on the top layer while the sim card holder is on bottom layer. When ever I give power to the SIM900, it responds to AT commands but when I try to do ATD<number>; it says SIM Card not inserted. Also the net light blinks with 64ms ON 800ms OFF, which means that it is not registered to the network. I have a few questions:
1) What is the voltage level at SIM VDD. I measured the voltage but the voltage was 0v. I know that SIM900 gives voltage (1.8v/3v) depending upon the SIM presence. But I am sure the SIM card is working fine.
2) I am using SMD diodes (IN5819). I did a test on them using multimeter diode test mode, on the both sides(black<->red & red<->black), it displays some value which according to this document is wronghttp://en-us.fluke.com/training/trai...ultimeter.html. But the diode which I have (through hole) shows exact reading as per the document. Is the diode faulty.?
3) Is the schematic correct. Do I need to make any changes into it. I am planning to make SIM card circuit on zero pcb and then attach all the SIM connections to the PCB. Please tell me if the SIM Card circuit is wrong.
27th December 2016, 07:15