Reading and Writing to an SD Card
Now you are going to learn the basics of writing to and reading from an SD Card. SD Cards are a small and cheap method of storing data, and an Arduino can communicate relatively easily with one using its SPI interface. You will learn enough to be able to create a new file, append to an existing file, timestamp a file, and write data to that file. This will allow you to use an SD Card and an Arduino as a data-logging device to store whatever data you wish. Once you know the basics, you will put that knowledge to use to create a time-stamped temperature data logger.
Project 42 – Simple SD Card/Read Write ...