Not able to send large number of samples over BLE

[shr217]

Hi,

I have an ADC which is interfaced with the nrf52.

The samples from the ADC are collected every 2ms (500Hz sampling rate). I store these samples, and when the number of samples stored equals to 100, I need to send it over BLE.

I have this system working for 25samples, however when I increase the count, no transmission occurs. (No samples seem to be received)

Each sample value is around 9 bytes.

Can anyone help me with this issue.

[Kenneth]

There is information missing here, for instance you are not writing how you are sending data (write command or notification), and if the softdevice api call to send data is returning any error code.

You write you want to send data in 100bytes "chunks" but how do you know that is the most efficient data size. Typically you want to include nrf_ble_gatt_init() if you want to send data that is longer than default 20byte, this can be handled by adding gatt_init() to your project.

I suggest to check out:
https://devzone.nordicsemi.com/f/nordic-q-a/41629/what-is-the-difference-between-data-length-and-mtu

Also you may find this useful:
https://www.novelbits.io/bluetooth-5-speed-maximum-throughput/

[shr217]

My particular application requires a process where it is interfaced with the ADC. I have a constraint that I cannot send the data simultaneously while sensing, which requires me to store it and then send.

So overall, it works such that I sense the data, then send and again sense. This process repeats. I need to send a burst of data.

I am using  ble_nus_data_send to send the data array

I tried to change the BLE_GATT_ATT_MTU_DEFAULT, but am not able to get it to send greater than 25samples at a time

[Kenneth]

29samples * 9bytes = 261bytes which is actually a decent large packet. 

shr217 said:

but am not able to get it to send greater than 25samples at a time

This sentence doesn't make sense, there must be some kind of error code somewhere (you may be ignoring it if you are not checking return err_codes).