Question

Please what is the operational principles and communication protocols of arduino and micro Sd card module. i will be connecting this by using the items listed below:

arduino uno

micro sd card

Arduino sd card module

jumper wires.

Answer 1

The SD card module is specially useful for projects that require data logging.

The Arduino can create a file in an SD card to write and save data using the SD library.

There are different models from different suppliers, but they all work in a similar way, using the SPI communication protocol.

SPI communication protocol:-

Serial peripheral interface (SPI) is an interface that enables the serial (one bit at a time) exchange of data between two devices, one called a master and the other called a slave .

The Clock

The clock signal synchronizes the output of data bits from the master to the sampling of bits by the slave. One bit of data is transferred in each clock cycle, so the speed of data transfer is determined by the frequency of the clock signal. SPI communication is always initiated by the master since the master configures and generates the clock signal.

Any communication protocol where devices share a clock signal is known as synchronous. SPI is a synchronous communication protocol. There are also asynchronous methods that don’t use a clock signal. For example, in UART communication, both sides are set to a pre-configured baud rate that dictates the speed and timing of data transmission.

The clock signal in SPI can be modified using the properties of clock polarity and clock phase. These two properties work together to define when the bits are output and when they are sampled. Clock polarity can be set by the master to allow for bits to be output and sampled on either the rising or falling edge of the clock cycle. Clock phase can be set for output and sampling to occur on either the first edge or second edge of the clock cycle, regardless of whether it is rising or falling.

Slave Select

The master can choose which slave it wants to talk to by setting the slave’s CS/SS line to a low voltage level. In the idle, non-transmitting state, the slave select line is kept at a high voltage level. Multiple CS/SS pins may be available on the master, which allows for multiple slaves to be wired in parallel. If only one CS/SS pin is present, multiple slaves can be wired to the master by daisy-chaining.

Multiple Slaves

SPI can be set up to operate with a single master and a single slave, and it can be set up with multiple slaves controlled by a single master. There are two ways to connect multiple slaves to the master. If the master has multiple slave select pins, the slaves can be wired in parallel.

Pin wiring:-

SD card module	Wiring to Arduino Uno
VCC	3.3V or 5V (check module’s datasheet)
CS	4
MOSI	11
CLK	13
MISO	12
GND	GND

Read and write to the SD card

The SD library provides useful functions for easily write in and read from the SD card.

To write and read from the SD card, first you need to include the SPI and SD libraries:

#include <SPI.h>
#include <SD.h>

You also have to initialize the SD card module at the Chip Select (CS) pin – in our case, pin 4.

SD.begin(4);

To open a new file in the SD card, you need to create a file object that refers to your data file. For example:

dataFile = SD.open("data.txt", FILE_WRITE);

The first parameter of this function is the name of the file, data.txt, and the FILE_WRITE ;argument enables you to read and write into the file.

This line of code creates a file called data.txt on your SD card. If the data.txt file already exists, Arduino will open the file instead of creating another one.

To write data to the currently open file, you use:

dataFile.write(data);

In which the dataFile is the file object created previously and the data is what you want to write in the file.

You can also use the print() or println() functions to print data into the file:

dataFile.print(data);
dataFile.println(data); // followed by a new line

To read the data saved on your file:

dataFile.read();

You can only write within a file at once, so you need to close a file before proceeding to the next one. To close the data.txt file we’ve just created:

SD.close("data.txt");