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

[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]

Hello,

Thanks for your information!  Is there some good suggestions or improvements for our system? 

Thanks, 

Jason Hu

[Andreas]

Hi,

 

The most evident suggestion would be to just direct the cable away from the nRF52. Alternatively you would need to make some coexistence communication, to avoid the GSM module transmitting when the nRF52 is enabled/receiving.

Alternatively, as they are fairly far apart in frequency, you could add a coexistence filter to the nRF52 path to improve attenuation of the out-of-band components from the GSM module.

Also is the cable outer conductor well grounded to the board?

 

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