iPhone short distance connection

[Franco Fischer]

Hi!

I'm developing a custom PCB with a NRF52840 which I made a custom firmware based on ble_app_uart example. I test my product with different phones, Android and Apple phones.

In Android, I have a good connection distance, like 6m to 8m, but in iPhone I have about 2m or less.

I changed the PHY from BLE_GAP_PHY_AUTO to BLE_GAP_PHY_2MBPS, can this change reduce the connection distance?

Thanks!

[Jimmywong2003]

Hi

First, you need to verify the 32MHz on your own PCB.  The loading Cap of the 32MHz, is it well-tuned or not?

Second,

You can try to use the shortest connection interval such as 30ms (default) or 15ms (min and max = 15ms).  It would help because it would have much more chance to do the retransmission.
also, are you using the internal RC or external 32KHz?
if using the internal RC, you can use a shorter calibration period such as 500ms instead of 4 sec.

https://jimmywongiot.com/2019/12/17/internal-rc-calibration-handling-on-the-nordic-nrf52-chipset/

if using the external 32KHz, you can change the PPM to bigger such as 250ppm (it would automatically increase the RX window.).

[Franco Fischer]

Yes, we verify the 32MHz on our PCB. We test 2 diferents boards transmiting a fixed carrier in 2.45GHz. We have a desviation about 50kHz (one board 50.24kHz and the other one 38kHz). It is good enough? We are developing a new version of the PCB to improve the crystal layout.

We have an external 32kHz clock, but right now we are using the internal one, we change the NRF_SDH_CLOCK_LF_ACCURACY to 500 PPM in the sdk_config and the NRF_SDH_CLOCK_LF_RC_CTIV to 16 and NRF_SDH_CLOCK_LF_RC_TEMP_CTIV to 2.

I will try to change the calibration period...

Thanks

[Marjeris Romero]

Good points from Jimmy on checking the crystal accuracy.

Franco Fischer said:

We have a desviation about 50kHz (one board 50.24kHz and the other one 38kHz)

The frequency tolerance requirement for BLE is depending of the packet lenght is of +-40ppm (packet length <= 200bytes) or +-30ppm (packet length>200bytes).
ppm= (deltafreq* 10^6)/carrier_freq

For delta of 50kHz this gives 20ppm, which is inside specs (but it could perhaps be a bit better).

Usually we use this formula to calculate the value of the crystal capacitors:

C1=C2= 2* C_load - 4pF

Where C_load value should be found in the crystal datasheet.

But in my experience what is usually the limiting factor in performance is poor RF layout, and specially poor grounding. We have some guidelines for PCB desing using nRF52 that are important to follow: https://devzone.nordicsemi.com/nordic/short-range-guides/b/hardware-and-layout/posts/general-pcb-design-guidelines-for-nrf52

Together with the reference layout for the chip your are using.

You can download reference files for the nRF52840 from the product page: https://www.nordicsemi.com/Products/nRF52840/Compatible-downloads#infotabs

If you open a private ticket we can take a look at your design before to give you a thumbs up before sending it for manufacturing in large quantities...

Best regards,

Marjeris