Need help to read data from SD card or pendrive to arduino

Using Arduino Project Guidance
#1

Hello guys,

I'm making one project in which SD card or pendrive has all the data. the data file contains one string and Two integers. i want to read all three data fields at a time and store in three different variables.

so, in which file format i can save the file in storage devices?

How i can read the data from storage devices and put in variables of arduino?

How many number of arduino's can access the same storage device at a time?

Thanks in advance.

#2

Generally, it you want to read data from a file on an Arduino you use one with an SD card socket or add a shield that has one.

File format is up to you. A text file is easy to read from.

Your last question is more tricky. In the scenario I described, the answer is obviously one. Are you planning to have the pen drive attached to a PC instead?

#3

shreekantha_v:
I'm making one project in which SD card or pendrive has all the data.

To use USB storage you would first have to add a USB Host Shield to most Arduinos. For an SD card you just need an SD socket connected to the SPI pins.

shreekantha_v:
the data file contains one string and Two integers. i want to read all three data fields at a time and store in three different variables.

You will need some way to determine the end of the string. If there is a marker character, use "file.readBytesUntil(marker, buffer, bufferSize)". For the integers, use "var = file.parseint();" which will read until it finds a number and then read until it finds the end of the number (or timeout).
https://www.arduino.cc/reference/en/language/functions/communication/stream/streamreadbytesuntil/
https://www.arduino.cc/reference/en/language/functions/communication/stream/streamparseint/

shreekantha_v:
so, in which file format i can save the file in storage devices?

I would use a text file. Given the choice, I would put the two integers first and then the string, ending with a newline character ('\n') as an end marker.

shreekantha_v:
How i can read the data from storage devices and put in variables of arduino?

You would use the file.read() functions.

shreekantha_v:
How many number of arduino's can access the same storage device at a time?

Just one, but that one could communicate with others to share the data.

#4

Have you looked at the SD library example sketches?

#5

Thank you very much for your response.

I'll try and see.

#6

Hello,

list = dataFile.readStringUntil('\r');

using \r or \n i can print the current line in a file. So, to print previous line what character i can use?

thank you

#7

Use file.position() to get the current file position. Save that in a variable. Use file.seek() to go back to that position so you can read that line again.

You can't read backward with readStringUntil(). Only forward.

#8