nRF52840, evaluation for BLE devices to be used in a test system

[WilliamMcCoy21]

I am in the conceptual stages of development for a BLE test system.

The test system requires:

Fast transceiver and connection with BLE devices, preferably capable of scanning for devices in ms (5ms or lower preferably) with a high data rate (1 Mbps).

Capable of calculating the BLE channel received and controlling the BLE channel used.

Controlled modulated RF wave transmission (optional).

The test requires the capability to communicate and connect with 6 devices in parallel, is the nRF52840 capable of connecting with multiple devices?

I am planning to create a PCB using the nRF52840 chip or similar which fits the requirements. Can multiple (up to 6 depending on the number of devices that can be connected) nRF52840 dongle with PCB Altium documents provided by Nordicsemi be used on one larger PCB without interference? the BLE circuits will; share solid inner layer ground and power sources with the ground vias placed close to the pins, be located close to the edge of the PCB, be routed to avoid noise on Vcc and the area of the antennas will have a keep out area with no traces or metal near. The PCB dielectric thickness will match that of the nRF52840 dongle to prevent an effect on the antenna.

https://www.nordicsemi.com/-/media/Software-and-other-downloads/Dev-Kits/nRF52840-Dongle/nRF52840-USB-Dongle---Hardware-files-2_0_0.zip

Can an external antenna then be added to the PCB using an SWF or similar surface mount RF connector?

[Kazi Afroza Sultana]

Hello William, 

Here are some explanation of your questions:

''what would be a typical data rate for this device? the previous hardware I have been using has had a very slow data rate due to the scan functionality taking a long time to begin, with the scan function being required to retrieve the advertisement. I am receiving up to 41 Bytes per advertisement packet, I want to be able to reliably receive this advertisement packet in milliseconds (the faster the better).''

In ideal condition, You can achieve around 200-300 kbps maximum data rate for 1Mbps of IM coded phy modulation rate when two devices are in 1m distance. For 2Mbps modulation rate, it (data rate) would be maximum 500 kbps for maximum 1m distance. More the distance increases, the sensitivity has to increase and data rate decreases. But there are other factors also involved here like radio interference by obstacle, Line of sight so not always we can get the ideal value. Increasing sensitivity can reduce the payload but the compensation is low data rate and high power consumption.

And the above mentioned data rates for different modulating rate are for single connection. When you have multiple connection, time gap between consecutives packets increase that reduces the data rate. Scanner is another functionality which occupies the timeslot of the connection. If you have scanner along with connections, then during that scan window the connected devices are not transmitting any data, so this will reduce the data rate. The longer the scan window the lower will be the data rate on the connected roles.

''Our softdevice offers a maximum of upto 20 connections, so connecting with multiple device is not a problem. ''

Each connection should read data from the paired device individually. Could you please elaborate this point ?

''is the nRF52840 capable of knowing the received BLE channel and transmitting on specific channels?''

The nRF52840 is not capable of selecting the channels in the connected state, only channel selection algorithm is configurable in connected states. In advertising and scanning states, you can choose which channel to transmit the adv packet or scan the incoming packet.  When both devices are in the connected states they know which channel to use as this is set at the negotiation during connection time. You can look at these previous tickets about channel selection. https://devzone.nordicsemi.com/f/nordic-q-a/27479/chsel-algorithm and (+) Configuring Advertisement channels and Connection channels - Nordic Q&A - Nordic DevZone - Nordic DevZone (nordicsemi.com) . 

Feel free to ask if you have more clarification. 

Best Regards,

Kazi Afroza Sultana