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| SIM800 GSM module does not detect SIM card |
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| Yansi:
Hello, my friend recently showed up with a question, whether I could figure out why is his SIM800 module not connecting to the network. I have never worked with GSM modules, but being a rather quick-learner... I soon obtained the reason: SIM800 does not detect SIM card. Asking the module AT+CPIN? returns error of "SIM not inserted". (using the extended error message set, AT+CMEE=2) I have investigated, what the VCC, RST and CLK pins on the SIM card look like. VDD seems correct, module gives the card four times a voltage pulse of 1.8, 3, 3 and finaly 1.8V again, for a duration of few tens of ms. Which seems okay. Then I've probed the CLK pin - but wait, there is nothing I could recognize as a CLK signal, please see attached pictures. The RST pin of the SIM card does not produce anything reasonable either - all reset pulses are only 0.8V high. Whatta? So Okay, I know why it is not connecting to the network, but it does not really explain why the voltage levels are as observed. Is the module really messed up (ready for some widlarizing action) or is this behavior normal? Thank you, Y. //first two pictures is the CLK signal (measured on different power-ups), third one is the RST pin. |
| Yansi:
Meh! I have finally found the problem: A damaged ESD diode array near the SIM slot. Either that, or wrong type of component, its orientation or such may have been wrong. So, for others that may stumble upon this thread: Whenever you have problems with detecting the SIM card, check for damage of the ESD array for the SIM card slot! In my case only the diodes were dud, SIM800 module okay. |
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