I am currently working on a project that needs to record data at a very fast rate and display it on a LCD. I have a code for that working. The next part I need to do is incorporate a SD card and get it to log the data onto that. I want it to have the time since it's started with the Analog reading from my sensor, for eventual excel plotting but do not know how to change my code to do this. I can get my readings to show on the serial monitor and plotter but have no idea how to get the SD card incorporated, coding wise. I also read about a method to stop writing data with a switch to protect against corruption. Can I just use a second analog input for this with "if" and "while" loops?

If any of you have written any arduino code similar to this, or know how this all might be done, please help.

Here is my current code in pastebin: https://pastebin.com/U3uQQBz1