UNIX timestamp information over BLE

[RO]

Hello,

I'm starting design on a new BLE dongle project. 

I am planning to use nRF52840 and an external flash memory for storing sensor data. I need to include timestamp information(UNIX time)  of each data point and send it over BLE, and create a historical time series graph on the phone. 

What is the best way to accomplish this? Do I need to add a Real Time Clock in the hardware? Is it possible to get UNIX time by somehow syncing with phone( without using real time clock)? Is timestamp sent over a separate service?

I cannot find good documentation for timestamp information and BLE on the internet. 

Please help,

Thanks

[Stian Røed Hafskjold]

Hi, you can check out the Current Time Application example in the SDK: https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v15.3.0/ble_sdk_app_cts_c.html?cp=5_0_4_2_2_7

It includes a Current Time Service (CTS) server that runs on nRF Connect, so I guess you would have to port this server to your smart phone application. Not sure what is native to iOS/Android.

You can use this service to sync with the RTC on the nRF52. The RTC running from an external crystal usually has an accuracy of 20ppm, so based on this you would have to calculate how often the clock has to be synced in order to meet your accuracy requirement.