Changelog

2019-02-22 (v 2.1.0)

Code cleanups (use functions, better comments)
Use more config variables
Drop delta from data output, but leave it in debug logging
Increase acceleration precision to 3 digits (configurable)
Use stop_us output to better coincide with acceleration timing (I think)

2019-02-19 (v 2.0.0)

Changed accelerometer from 4G to 8G range.
Changed acceleration output from m/s² to G since it's metric/imperial agnostic.
Called lis.read() directly instead of lis.getEvent() for a very small speed boost (but mostly to avoid conversion from G to m/s².
Set accelerometer to faster data rate (unsure this has an effect due to issues in the library).
Use SDFat library to support long filenames.
Uses a full timestamp for the output filename (e.g. 201902171830.csv).
Set I2C speed to fast mode.
Define the column units (e.g. µs, G) in the header row to reduce disk usage.
Dropped millis() from output (same info provided by micros()).
Dropped battery voltage from output.
Dropped acceleration range from output (inconsequential).
Use unsigned long variables to reduce overhead.
Call the unixtime() just once at start up and use micros() to estimate time afterward (shaved off 30ms per loop).
Dropped the motion-detection aspect of data writing and simply write the data to the SD card every 800 loops.

2019-01-04 (v 1.0.0)

Initial check-in