Hi there, and Welcome.
Have you tried swapping the echo and trigger pins?
Are you able to leave the BLE stuff out and get it to display the reading on the serial port?
Also maybe inverting the logic for the 10us. pulse generation. The error sounds like it’s NOT liking the timing of it?
Are you saying when you try the BLE connection it throws the error?
In your Read BLE , Do you define the length of the string or vale (digits)
What Board support package , mbed or non? for the Nrf52840
You are close though…
HTH
GL 
PJ
1 Like