Writting data from arduino and reading it.

Is it possible to write data from arduino onto a csv or excel file and read the file to get data for processing ?

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Of course it's possible, but details depend on where the file resides, and the way data are sent to the file. In the simplest case the Arduino sends data via Serial, and a program on the PC writes the data to the file.

You could send the data directly to Processing (for processing) via serial, then if you still need a csv file then Processing could create it.

I'm quite certain that the SD card library for Arduino is organized as a mini-file system. SD cards are cheap, easy to hook up, and nicely portable. You can open a file on the SD card, write data to it, close it, pull the card, and insert it into another computer.