[BC66] SIM related errors on custom PCB

Recently we made a prototype PCB which includes a BC66 module, a main MCU and a USIM card holder. Communication between the main MCU and the BC66 is going fine, however all SIM related commands are giving errors. These include: “AT+ QCIDD”, “AT+CPIN?”, “AT+CIMI”. See output below. The SIM card itself seems to work fine in other devices though.

That leads me to think there is a problem with the connection between the BC66 and the USIM card holder. See image below for schematics. I’ve also attached a reference design diagram from the BC66 hardware design guide. As far as I can tell our connections are correct, except for the missing TVS. Could that be a cause for problems?
We also forgot to add the POWER_KEY connector / button. So now I’m briefly holding a wire between GND and the PWR_KEY to power on the BC66.

Any help would be much appreciated!

11:48:59.529 -> ATI
11:48:59.624 -> 
 Revision: BC66NBR01A11

11:49:09.208 -> Set APN / CGDCONT
11:49:09.302 ->  OK
11:49:10.807 -> 
11:49:11.786 -> Check operator
11:49:11.881 ->  +COPS: 0
11:49:13.340 -> 
11:49:13.340 -> # Module IMEI-->  
11:49:13.387 ->  +CGSN: 86799703656XXXX
11:49:14.879 -> 
11:49:15.863 -> # Firmware ver-->  
11:49:15.956 ->  +CGSN: 31

11:49:24.532 -> USIM card identification - AT+QCCID
11:49:24.578 ->  ERROR
11:49:26.037 -> 
11:49:26.037 -> USIM card identification - AT+QCCID
11:49:26.083 ->  ERROR
11:49:27.589 -> 
11:49:27.589 -> USIM card identification - AT+QCCID
11:49:27.636 ->  ERROR
11:49:29.124 -> 
11:49:29.124 -> USIM card identification - AT+QCCID
11:49:29.172 ->  ERROR
11:49:30.626 -> 
11:49:30.673 -> USIM card identification - AT+QCCID
11:49:30.673 ->  ERROR
11:49:32.178 -> 
11:49:32.178 -> Is a PIN needed for the SIM card? AT+CPIN?
11:49:32.225 ->  ERROR
11:49:33.729 -> 
11:49:33.729 -> Is a PIN needed for the SIM card? AT+CPIN?
11:49:33.775 ->  ERROR
11:49:35.222 -> 
11:49:35.222 -> Is a PIN needed for the SIM card? AT+CPIN?
11:49:35.268 ->  ERROR
11:49:36.764 -> 
11:49:36.764 -> Is a PIN needed for the SIM card? AT+CPIN?
11:49:36.811 ->  ERROR
11:49:38.310 -> 
11:49:38.310 -> Is a PIN needed for the SIM card? AT+CPIN?
11:49:38.357 ->  ERROR
11:49:39.809 -> 
11:49:39.857 -> Is a PIN needed for the SIM card? AT+CPIN?
11:49:39.857 ->  ERROR
11:49:41.346 -> 
11:49:41.346 -> Is a PIN needed for the SIM card? AT+CPIN?
11:49:41.393 ->  ERROR
11:49:42.895 -> 
11:49:42.895 -> Get SIM identity - AT+CIMI
11:49:42.943 ->  ERROR
11:49:44.404 -> 
11:49:44.404 -> Get SIM identity - AT+CIMI
11:49:44.451 ->  ERROR
11:49:45.955 -> 
11:49:45.955 -> Get SIM identity - AT+CIMI
11:49:46.002 ->  ERROR
11:49:47.506 -> 
11:49:47.506 -> Get SIM identity - AT+CIMI
11:49:47.506 ->  ERROR
11:49:49.009 -> 
11:49:49.009 -> Get SIM identity - AT+CIMI

The SIM card can be detected by your circuit design,although there are some differences from the reference design we provided.
I suggest you check the following aspects:
1、Do all devices have this problem, or does your current initial device have this problem?
2、You can solder the pin of the SIM card holder directly to the corresponding pin of the module to check whether the card holder is abnormal.
3、Check for short circuit or cross welding problems.

Hi @herbert.pan-Q ,

Thank you for the suggestions. I have tried with another PCB of the same batch, and it gives the exact same problems as the initial one.
I have also checked for welding and short circuit problems. Nothing seems to be out of the ordinary.

One thing I noticed is that when I connect to the debug UART port on the BC66 (using Putty), I receive no characters. I’m not able to use UE monitor because I don’t have a “message definitions file” for this module, but I would expect to at least see some characters coming through even without using UEMonitor. I find that strange, do you think that might be related to the problem?

Many thanks

1、I recommend that you weld the pin of the SIM card holder’s pin directly to the pin of the module. This is also allowed and can be used to troubleshoot your circuit design problems.

2、UE Monitor is not a BC66 log capture tool. If you need to capture debug port logs, you need to use another tool. URAT debugging tools can be downloaded from the link.

1 Like

I had a similar SIM issue on a custom PCBA. The problem turned out to be that the orientation of how the SIM card needed to be inserted into the holder was different than I expected. The holder I was using required the SIM’s chamfered corner to be outward.

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Hello ,
What is answer for AT+CFUN?


  • Capacitors need place closer to the SIM connector, then resistors
    Search issues:
    Replace 22 Ohm resistors o 0 Ohm, then unsolder all SIM capacitors.

Thanks for the suggestions.

@herbert.pan-Q , I haven’t tried that yet because I don’t have such an external SIM connector. But I’ll see if I can get one.

I noticed that I was doing this wrong too, thanks for the suggestion! I’ve changed it around now, but it hasn’t made much difference unfortunately.

CFUN = 1. See logs.

what is CFUN value?

 +CFUN: 1

USIM card identification - AT+QCCID

 +CME ERROR: 772

USIM card identification - AT+QCCID

 +CME ERROR: 772
Is a PIN needed for the SIM card? AT+CPIN?

 +CME ERROR: 772

Is a PIN needed for the SIM card? AT+CPIN?

 +CME ERROR: 772

Error 772 means that the USIM is powered down according to the manual. When I measure the voltage of SIM_VDD I measure 0 V. Strange behaviour. In this post it is explained that the voltage drops to 0 V after an initial startup sequence.

I think need check sim holder,(sim cart) <-> module connection lines.
Replace 22 Ohm resistors to 0 Ohm, then unsolder all capacitors on SIM holder line.
Connect a Sim holder to module directly.
is SIM cart OK? Does it work in other solution?
Change module :slight_smile:

Hi @KvX , yes the SIM card works in BC95-G dragino modules. So far it hasn’t worked in our own custom PCB BC66 modules.

I have tried it with a different BC66 PCB, and now I get more of a response:


USIM card identification - AT+QCCID


Is a PIN needed for the SIM card? AT+CPIN?


CME Error 10 means that the SIM card is not inserted (even though it is).

So does that mean the connection with the SIM connector at least is okay?

Could it mean that there is a mismatch between the polarity / type of SIM card and the SIM card holder/connector?

Update: I removed all the capacitors from the SIM connection, and have also replaced the resistors to 0 Ohm as per @KvX suggestion. I also added a piece of paper above the SIM so that the Nano SIM card pushes harder against the pogo-pin-like contacts. Another thing I did is cut off a little bit from the corner (opposite the chamfer) of the nano SIM so that it goes into the SIM holder well and activates the clicking mechanism.
I also increased the power supply so that it is able to deliver 2 A worth of current if the module requires it.

yet, I still get the same response, +CME ERROR: 10.

Could it be that the SIM holder is not suited to NB IoT SIM cards? This is the one I’m using.

Check AT+CFUN? again

SIM Holder for Nano SIM?

i think remine this one suggestion
In other case must work. dont see any more problem

Still the same.

+CFUN: 1 

Yes I’m using a SIM holder for Nano SIM, and I’m using a Nano SIM card.

I’ll see if I can order a seperate Nano SIM holder to do this with.

Problem resolved! What did the trick:

  • I bypassed the voltage regulator on the PCB, and connected it straight to a power supply capable of delivering 1 A. The PCB voltage reg only delivers 300 mA
  • I removed (with some plyers) R10, C16, C17, C15, C18, C23. See the schematics at the top of this post.

Thanks everyone for the help!