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I have a SIM908 module on a dev kit board. I have three SIM cards that are all detected fine on the previous version of the board. However, the v2 only detects one out of the three SIMs. I put the scope on while it was trying to detect one of the non-working ones and saw that it attempted at 1.8v and got no ATR back, then at 3v and got no ATR, then gave up (neither module supports 5v SIMs, but I gather they went out in the 90s anyway).

The module is adequately powered (2.5A continuous, 4A peak; module is only 2A peak). I have confirmed good connectivity between the module pins and the SIM card holder.

To reiterate, all three SIMs are detected by the v1 board, which uses the same module. What could be wrong, and what else can I try?

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  • \$\begingroup\$ I don't suppose there's a good datasheet / user guide you can link to? But if that red button is reset (or maybe you can try AT+CFUN=0 followed by AT+CFUN=1 instead) does it make a difference? \$\endgroup\$
    – PeterJ
    Nov 25, 2013 at 7:03
  • \$\begingroup\$ simcom.us/product_detail.php?cid=1&pid=38 \$\endgroup\$
    – Isvara
    Nov 25, 2013 at 18:24
  • \$\begingroup\$ I'd look at the working module and see what it does differently. You mentioned looking at a failed detection... but not if you compared that to the other module with the same SIM on the scope. \$\endgroup\$
    – darron
    Jan 3, 2014 at 6:05

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