Question about starting a data record based on a specific input...

Projects Programming
1

Hi all, my question is about recording data string to an SD card but only after a signal on an analog input s found.
The set up is data logging 5 analog sensors but I also want to be able to connect via Bluetooth to retrieve the recorded data from sd to a pc. I assume (and I'm new) that it currently starts recording as soon as its powered up (which it does) but I then assume that since it behaves like this I would be able to retrieve data from SD via Bluetooth. SO if it was set-up to not record until it received a signal from the analog input (in this case rpm) then I would be able to read files off SD.

Any ideas here on how to write the code?
THanks

2 
if (analogRead(analogPin) >= threshold)
{
  startRecording = true;
}

if (startRecording)
{
  //record data 
}