Oct 24, 2013 #1 M micro-hopless Member level 1 Joined Sep 12, 2007 Messages 41 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,551 I'm using a SIM900 modem for connecting to a GPRS network, but the stupid modem will not recognize ANY SIM attached to it ! I have double, triple quadruple check the SIM connections but it won't work !. I have zero volts on SIM_VDD pin, with 10uF cap to ground. The SIM_PRESENCE pin is connected to ground. Modem responds to all AT commands, and is still in autobauding mode, which I wish to keep. What is wrong?
I'm using a SIM900 modem for connecting to a GPRS network, but the stupid modem will not recognize ANY SIM attached to it ! I have double, triple quadruple check the SIM connections but it won't work !. I have zero volts on SIM_VDD pin, with 10uF cap to ground. The SIM_PRESENCE pin is connected to ground. Modem responds to all AT commands, and is still in autobauding mode, which I wish to keep. What is wrong?
Oct 24, 2013 #2 N Nagesh29 Junior Member level 2 Joined Oct 9, 2013 Messages 22 Helped 1 Reputation 2 Reaction score 1 Trophy points 3 Activity points 129 Are you getting the proper supply voltage at SIM900 modem?
Oct 24, 2013 #3 M micro-hopless Member level 1 Joined Sep 12, 2007 Messages 41 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,551 4.05V on the dot ! netlight blinks happily. - - - Updated - - - VDD_EXT is 2.824V
Oct 24, 2013 #4 T trastikata Member level 1 Joined Apr 28, 2007 Messages 36 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,631 Did you check the voltage drop?
Oct 24, 2013 #5 N Nagesh29 Junior Member level 2 Joined Oct 9, 2013 Messages 22 Helped 1 Reputation 2 Reaction score 1 Trophy points 3 Activity points 129 I think you need to increase your voltage. The let will blink at low voltage also. But sim detection needs some higher voltage level.(Exact 5V)
I think you need to increase your voltage. The let will blink at low voltage also. But sim detection needs some higher voltage level.(Exact 5V)
Oct 24, 2013 #6 M micro-hopless Member level 1 Joined Sep 12, 2007 Messages 41 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,551 There isn't any voltage drop. The filter capacitor for VBAT is 3300uF. - - - Updated - - - VBAT is 4.05V, not my mcu power supply. - - - Updated - - - The datasheet says that SIM900 must be powered between 3.2 and 4.8V, on the VBAT pins.
There isn't any voltage drop. The filter capacitor for VBAT is 3300uF. - - - Updated - - - VBAT is 4.05V, not my mcu power supply. - - - Updated - - - The datasheet says that SIM900 must be powered between 3.2 and 4.8V, on the VBAT pins.
Oct 24, 2013 #7 N nick703 Advanced Member level 1 Joined Oct 17, 2011 Messages 422 Helped 21 Reputation 44 Reaction score 22 Trophy points 1,298 Location surat Activity points 3,987 i think u post your ckt diagram and why u use SIM_PRESENCE pin to gnd ?
Oct 24, 2013 #8 T trastikata Member level 1 Joined Apr 28, 2007 Messages 36 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,631 Did you use a multimeter or an oscilloscope to check the voltage drop? Also see if all of the module's ground pins are connected to GND. If you can, post the scheme maybe someone can see something you missed - could happen to everyone.
Did you use a multimeter or an oscilloscope to check the voltage drop? Also see if all of the module's ground pins are connected to GND. If you can, post the scheme maybe someone can see something you missed - could happen to everyone.
Oct 24, 2013 #9 M micro-hopless Member level 1 Joined Sep 12, 2007 Messages 41 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,551 modem connections - - - Updated - - - I've used a scope to check the voltage drop.
Oct 24, 2013 #10 T trastikata Member level 1 Joined Apr 28, 2007 Messages 36 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,631 What is the purpose of C42 to ground on the clock line?
Oct 24, 2013 #11 M micro-hopless Member level 1 Joined Sep 12, 2007 Messages 41 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,551 Supposedly for EMI protection. I've removed C41 and C42, but no change.
Oct 24, 2013 #12 T trastikata Member level 1 Joined Apr 28, 2007 Messages 36 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,631 You might be out of luck with a defective module, check with another module if possible. Other than that I don't see a reason why shouldn't be working
You might be out of luck with a defective module, check with another module if possible. Other than that I don't see a reason why shouldn't be working
Oct 24, 2013 #13 M micro-hopless Member level 1 Joined Sep 12, 2007 Messages 41 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,551 All FIVE modules that I have acquired behave the same ! - - - Updated - - - Anybody has some working pseudo code (sequence of commands, with responses) available, just to verify that I give it the correct commands.
All FIVE modules that I have acquired behave the same ! - - - Updated - - - Anybody has some working pseudo code (sequence of commands, with responses) available, just to verify that I give it the correct commands.
Oct 25, 2013 #14 M micro-hopless Member level 1 Joined Sep 12, 2007 Messages 41 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,551 so nobody has any pseudo code ?
Oct 25, 2013 #15 N nick703 Advanced Member level 1 Joined Oct 17, 2011 Messages 422 Helped 21 Reputation 44 Reaction score 22 Trophy points 1,298 Location surat Activity points 3,987 means some SIM900_AT command sequence?
Oct 25, 2013 #16 M micro-hopless Member level 1 Joined Sep 12, 2007 Messages 41 Helped 1 Reputation 2 Reaction score 1 Trophy points 1,288 Activity points 1,551 GOT IT ! The SIM connector pinout was given in an incorrect order in it's datasheet, so even if the footprint was ok, the actual pinning was not ! Now it works.
GOT IT ! The SIM connector pinout was given in an incorrect order in it's datasheet, so even if the footprint was ok, the actual pinning was not ! Now it works.
Oct 26, 2013 #17 Batang Member level 5 Joined Aug 16, 2012 Messages 84 Helped 28 Reputation 56 Reaction score 28 Trophy points 1,298 Location Malaysia Activity points 1,717 The SIM VCC capacitor (C40) should be 220nF. Cheers.
Oct 29, 2013 #18 N Nagesh29 Junior Member level 2 Joined Oct 9, 2013 Messages 22 Helped 1 Reputation 2 Reaction score 1 Trophy points 3 Activity points 129 @micro-hopless https://nageshjoshi.wordpress.com/2013/04/20/tcp-communication-using-gprs-modem/ You can try the above link for SIM900 AT commands along with the responses.
@micro-hopless https://nageshjoshi.wordpress.com/2013/04/20/tcp-communication-using-gprs-modem/ You can try the above link for SIM900 AT commands along with the responses.
Oct 30, 2013 #19 S Shadow_Wanderer Newbie level 2 Joined Jan 16, 2013 Messages 2 Helped 0 Reputation 0 Reaction score 0 Trophy points 1,281 Activity points 1,287 EMI protection move to SIMcadr side !!! SEE DATASHEET !!!