nRF52832: disconnect --> timeout 0x08 with GSM/GPRS module data transmitting

[knowic]

Hello,

We are using the nRF52832 and 2G(GSM/GPRS) module to build up one IoT product. We got a disconnect between nRF52832 with other master instance(mobile phone APPs) when there is data sending/receiving with 2G tunnel(900M/1800M). The reason we  get printed (p_ble_evt->evt.gap_evt.params.disconnected.reason) is 0x08(connection timeout).

Our board is look likes as this:

We suspect the EMI/EMC for disconnection reasons,  if we move the 2G cable to opposite direction(far from 2.4G BLE PCB antenna), there are no disconnection issues.

Could you help to share the detail reason for this and is there any improvements for it?

Thanks so much!

Jason Hu

[Andreas]

Hi,

 

The GSM module is probably blocking the nRF52832 reception. Even though they are quite distant in frequency, the signal power from the GSM module is high enough that it will block the nRF52832 receiver.

 

Best regards,

Andreas

[knowic]

Hi,

We have tried several method with hardware change to get it solved in the past month, but found no improvements .

1. Place magnetic bead on the power path of nRF52832, isolate it with other blocks

2. Add 2.4G filter/SAW on the RF input of nRF52832

3. Seperate away nRF52832 + ANT with the GSM+IPEX cable

Since the PCB board is installed in a plastic box which placed in a metal shell of smartlock, and GSM radio may be reflected in the sealed-off space.  So, if there any other further solution? 

Also, I have some question about the  "avoid the GSM module transmitting when the nRF52 is enabled/receiving.".

1. Can we keep the BLE link alive while disable receiving when the GSM is transmitting?

with my case, we use APPs to connect the  devie via BLE, but don't hope the link is broken when there are GSM transmitting

2. Can we decrease the sensitivity of nRF52832 to avoid the blocking ?

thanks again!

Jason Hu

[Andreas]

Hi,

 

Is it not an option to direct the cable away from the nRF52832 when the device is mounted in the enclosure? I also notice you have solder pads for a shield can around nRF52832, does adding this help?

 

You can try to use the PA/LNA optional interface to toggle a GPIO when the nRF52832 Radio has a RX event, if your GSM module supports it that could keep it from transmitting when the nRF52832 is in RX.

 

There is no way to decrease sensitivity of nRF52832 to avoid the blocking except filtering externally, which you said did not help.

 

Have you monitored the supply line or if the nRF52832 resets when the GSM module turns on? If the supply can't keep up, causing a >300mV step, the nRF52832 might reset.

 

Best regards,

Andreas

[knowic]

Hi, Andreas,

Thanks for your quick reply.

1. Now we direct the cable away as far as possible, but didn't change the result.

    We are trying to  add the  metal shield shell , and haven't  get result now.

2. What about the PA/LNA interface, is there any guide or documents about the operation of SDK?

3.Base on this product, we didn't see any reset phenomenon,  But our other product (BLE + NB-IoT) , we did see some individual device get the random reset randomly, we have not get the final reson about the reset, it is also not easy to get why.

BR,

Jason Hu

[Andreas]

Hi,

 

See this link for an example on how to use the PA/LNA interface. Additional information can be found in the Softdevice specification for your version.

 

nRF52832 can be reset if there is a step in the supply rail. Power-on Reset does not leave any bits set in the RESETREAS register, which might be a clue itself.

 

Best regards,

Andreas