[Moved] SIM900 Module SIMVdd not working - ERROR and AT reporting no Sim Card

[mtechautomotive]

Hi,

So we have created a PCB that uses the SIM968 module, and we originally used the EVB to test our control code and it all worked fine, sending texts etc.

So we then laid out the system as per the datasheet (design guide).

We get an error over AT (not specified) but we have the LED flashing - the error code is (is cant remember first bit, will post tomorrow AM) but it says 0,0 (meaning no sim detected.) SimVDD also remains at 0v or very close to 0v

To get round this I have tried (as suggested by other posts on this forum):
1. Adding some more capacitance on SimVdd to .22uf as others have said - no effect. (I have 100nF as per datasheet)
2. Pulling Sim Detect LOW - no effect
3. Even tried powering the SimVDD with external supply at 1l8 and 3.0 and still same error.

The PSU is as recommended switch mode 3.8v and there are no ripples/drops that I can see. - Would it even try and burst if the fail is Sim card check?

Please see the attached images for my schematic and layout.

Any help very much appreciated as it is a strange one! If anything needs testing please post and I will test and report, without second guessing.

Regards,
Matt

 

[Batang]

Hi a few things:

1. SIM Vdd capacitor ideally should be 220nF.
2. SIM detect no need to use or have a pull up resistor.
3. Vbatt depending on your power supply may need to be 1,000uF.

I do not think however that any of the above is causing your problem but I do think it maybe be the connections to the SIM socket.

Perhaps if you give a link to the datasheet for the SIM socket I can advise further.

Cheers.

 

[mtechautomotive]

Hi Batang,

Thanks for your feedback - turns out it was the sim connections. Farnell 2291185 - they number 1,5,2,6,3,7,4,8 not 1,2,3,4,5,6,7,8 as I did - what a muppet!

We have changed the SimVDD cap to .22uf, as for PSU we have used the recommened SMPS.

Have ordered a breakout board to solder the connections for sim card again, and will give a final report on this next week - fingers crossed.

I think may others with the same fault (plenty on this forum) really do need to check connectivity - simple mistake causes the exact issues reported by others.

Cheers
Matt

 

[Batang]

Hi Mat,

Great it's working.

Cheers.