iPhone short distance connection

RE: iPhone short distance connection

Marjeris Romero — Thu, 09 Sep 2021 20:37:26 GMT

Good points from Jimmy on checking the crystal accuracy.

[quote user="Franco Fischer"] We have a desviation about 50kHz (one board 50.24kHz and the other one 38kHz)[/quote]

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

RE: iPhone short distance connection

Marjeris Romero — Thu, 09 Sep 2021 20:17:29 GMT

No problem. You can open a private ticket and send us the schematics and layout for review already before manufacturing.

RE: iPhone short distance connection

Franco Fischer — Thu, 09 Sep 2021 15:58:25 GMT

Thanks for the reply. I am developing a new version of the PCB, I would really appreciate if you could give me some feedback. When I have the PCB ready I will send it.

Thanks

RE: iPhone short distance connection

Franco Fischer — Thu, 09 Sep 2021 15:45:07 GMT

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

RE: iPhone short distance connection

Jimmywong2003 — Thu, 09 Sep 2021 15:20:55 GMT

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.).

RE: iPhone short distance connection

Marjeris Romero — Thu, 09 Sep 2021 14:49:28 GMT

Hi,

Yes, 2Mbps will mean a small range reduction but with the benefit of increase data rate (‘high speed’ mode) and reduce average power consumption.

But the range you are getting seems a bit low anyway for both 1M and 2M. Have you previously had a schematics and RF layout review done by us on your custom PCB? And have the radio and antenna matching components been tuned? Feel free to submit your files for review either to this ticket or through a private ticket if you don't want to disclose design information. We can also assist with RF tuning.

For more information about what parameters affect Bluetooth range please take a look at the following resources:

Range estimator (scroll down on the webpage): https://www.bluetooth.com/learn-about-bluetooth/key-attributes/range/

Blogpost about Bluetooth range: https://blog.nordicsemi.com/getconnected/things-you-should-know-about-bluetooth-range

Best regards,

Marjeris