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I bought this SIM800C development board (vendor unknow):

Development board - front Development board - back

I conected it to an Arduino and put a brand new SIM card in it. This is the model of SIM I'm using:

Nano SIM card

Problem is, development board doesn't detect SIM card:

at+cfun=1,1    
OK
at+cpin?    
+CME ERROR: SIM not inserted
at+csmins?    
+CSMINS: 0,0

This is the scenario:

  • 6 pin SIM in a 6 pin SIM card holder.
  • SIM works fine in a cel phone. Send/receive voice call/sms.
  • Older, working SIM from various providers doesn't get detected either.
  • Every other non-SIM related aspect works.
  • No reboots, no flickering.
  • Board takes care of regulating voltages and signal levels.

I put an oscilloscope probe on the SIM_VDD pin (against board ground) and got this on every power-on:

Sim VCC on startup

Two 1.8v and two 3v pulses. That's all.

Please, note that I have no access to all SIM connexions (multi layer PCB).

How do I solve this problem?

migrated from iot.stackexchange.com Jun 29 '17 at 10:29

This question came from our site for builders and users of networked sensors and control devices in the contexts of smart homes, industry automation, or environmental sensors.

  • 1
    In this project I'm using a nodeMCU for green-house control and a SIM800C for remote access. This is very IoT to me. – user31481 Jun 24 '17 at 8:10
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    How are you powering the board? – TisteAndii Jun 24 '17 at 11:27
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    You might ultimately have IoT plans, but your question has nothing to do with IoT. And the idea that only IoT people have awareness of this is absurd beyond reason. – Chris Stratton Jun 24 '17 at 15:38
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    @TisteAndii. The board is powered with a 10V - 1.5A power supply. Yes, it is less than 2A, but I'm not transmitting or receiving anything. – user31481 Jun 24 '17 at 19:50
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    Best you try with a 2A supply to rule out the possibility that your supply cant yield enough current. Maybe pass the 10V supply through a buck first. Your SIM looks like it was shut off from power after initial attempts to power it failed. – TisteAndii Jun 24 '17 at 19:56
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The print on the PCB and product description at sellers site states it is GSM/GPRS board. The module on the board comes from SIMCom. This particular SIM800 module seems to have following capabilities as per SIMCom:

  • Compliant to GSM phase 2/2+
  • GPRS multi-slot class 12/10
  • Quad-band 850/900/1800/1900MHz

I think at the best you can only use a 2G SIM card on this board. Any 3G/4G SIM will not work.

Thanks for those images in the problem description, it gave me relevant keywords to search.

  • I tested with an old SIM (no 2G, 3G or 4G marking ), circa 2007, and same result. – user31481 Jun 23 '17 at 15:28
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    According to several Internet sources, you can mix 2G/3G/4G SIM cards with 2G/3G/4G cel phones. I think the same apply to this board. – user31481 Jun 23 '17 at 15:36
  • @LookAlterno, here's the generally supported combinations. 4G phone supports 4G/3G/2G SIM. 3G phones support 3G/2G SIM. 2G phones support only 2G SIMs. Backward compatibility is the norm. The cellular modems are built to be backward compatible. – sob Jun 23 '17 at 15:46
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This is a hardware problem.

We have experience the same issue in the company I'm working for and after a short discussion with a SimCOM Engineer we conclude it was a soldering issue. The problem may lies in the PCB or inside the SimCOM module. In both cases some part/parts are not soldered or the solder contact is broken. If the problem is outside you may fix it by inspecting the parts. If it is inside the SimCOM module there are very little you can do with the usual tools.

Just to be clear I quote a little bit of the discussion

Original question to SimCOM: enter image description here

A)We apply a zero pulse to PWR-key pin as you can see in the channel-1(yellow line)
and immediately the SIM800c module wakes up, the net and status led pins
become active (one led on the other blinks).

B) After a short time <1.5sec the SIM800c deploy a signal to SIM_VDD pin
(channel-2 - blue line)

Now in some boards the SIM_VDD pin goes to 1.8V as it appears in the
first of the 4 pulses and stay there. This situation is true if there is
a SIM card in the slot and the SIM800c is working properly. In that case
we can proceed and register to the network, send SMS etc...

In some boards though, as you can see in the screenshots, the SIM800
seams not to recognize the SIM card and tries again with 2 more pulses in
3V and one last one in 1.8V. The behavior is like there is no SIM-card in
the slot. Just to be clear. The SIM card is the same in all tests.
VBAT=3.9V, SIMVDD produced fine at 2.8V etc... The boards are identical
and no further code with AT commands is running.

Quite final answer from SimCOM:

It must be a soldering issue then. Did they followed recommended Solder
Reflow Profile?
https://www.elecrow.com/download/SIM800C_Hardware_Design_V1.02.pdf page 46

Please ask them where they measured signal from the scope pictures. From
the SIM card pins? If no, can they repeat that on them and send pictures.

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