nRF52811 shows up, but cant connect bluetooth.

[Mathias Lundberg]

So, i have created a custom board using the nrf52811 SoC. I tried to upload some bluetooth examples to it, and i can see the device on the nRF connect APP. The problem is i cant connect to it. It has a very high latency so i wounder if there could be a problem with my antenna design. Im using a tiny inverted F antenna design. Does anyone know what is wrong? could there be something else? Or maybesome has a better antenna design i can use? The only problem is that is has to be tiny. 

[Fredrik Sannerhaugen]

I have the same exact issue

[Kazi Afroza Sultana]

Hello Mathias,

We would like to see the design of your board. Could you please send both of the schematic and pcb design? 

Thanks.

Best Regards,

Kazi Afroza Sultana

[Mathias Lundberg]

Hello Kazi,

Im using the reffrence design from the documentation for the nrf52811 QFN32 using the internal LDO setup. Im not using the optional crystal. (I dont know if have have to specify this in the config somewhere). Here are the PCB design top and bottom im using. You can see the inverted F antenna in the middle. The 2 biggest VIAS is where i connect my power supply. Im fairly new to SoCs and antennas so please keep that in mind.

The name of the components is the same as they are in the reffrence design. The IR is an LED im working on.

[Kazi Afroza Sultana]

Hello Mathias,

Thanks for your design. 

I have looked at the design.

Antenna in the middle is not a recommended design and there is not enough ground plane in entire design (no ground plane on top). A matching network is needed between the RF pin and the antenna impedance normally 50 ohm) to the optimum RF load impedance for the chip. In addition to this , the two vias near antenna are quite big. 

You can look at our reference design https://infocenter.nordicsemi.com/topic/ps_nrf52811/ref_circuitry.html?cp=4_4_0_6_2_2#unique_140383198 and we have white paper that describes antenna tuning https://infocenter.nordicsemi.com/pdf/nwp_017.pdf?cp=17_15 .

Looking at these issues perhaps you need to redesign to get the Bluetooth connection. 

Thanks.

Best Regards,

Kazi Afroza Sultana