Transmitting data from SD card through Arduino – Neurolab record feature

In the Neurolab-Android app, we have been using an Arduino board for development as a workaround to the actual Neurolab hardware which is currently in the manufacturing stages. Along with the Arduino, we use a Micro SD card module with an SD card attached containing a dataset file in it. This combination of the Arduino and the SD card module serves as the source of dataflow into the Android app.

Firstly, we need to get the Arduino programmed for reading the dataset file from the SD card in the SD card module. We program the Arduino using the Arduino IDE on any desktop platform.

1. Import required libraries before starting off, namely the SPI and SD libraries for serial communication and SD card related functions respectively. Let us also set up some constant values which are going to be used in various parts of the code needed to program the Arduino for our required purpose.

#include <SD.h>
#include <SPI.h>
int baudRate = 9600;
int chipSelect = 4;
String fileName = "Dataset1.csv";

The ‘chipSelect’ variable denotes the chip select pin number for the connected Micro SD card adapter (module).

The baud rate for the Arduino board has been set to 9600 as a default. The dataset stored in the SD card from which the data needs to be read has been named “Dataset1”.

2. Next, we will need to initialize the SD card to check even if an SD card is inserted or not in the SD card module. We create a function for this purpose named ‘initializeSDCard’ in the following way:

bool initializeSDCard() {
  if (!SD.begin(chipSelect)) { 
    return false;   }
  return true;
}

The function will return true if initialization was successful. An unsuccessful initialization may also be due to the fact of SD card corrupted apart from not being properly inserted into the module.

3. Now we will be opening the dataset file from the SD card, making it ready to be read from.

File openTheFileFromSDCard(String fileName) {
  File file = SD.open(fileName);  
  if (!file) {
    Serial.println("error opening: " + fileName);
    return file;
  }
  return file;
}

The function will take in the file name as an argument and open it from the SD card. If the file is not found in the SD card, it will simply print out an error message to the serial output. It returns the file object in a true or false context accordingly.

4. We are now going to read data from the dataset in the SD card line by line using a function. The dataset file instance is passed as an argument to this function. This file is read and transmitted over the serial output channel line by line with ‘\n’ as the line delimiter, skipping null lines.

void readFromSDCardToSerialOutputLineByLine(File file) {
  String line;
  while (file.available()) {
    line = file.readStringUntil('\n');
    line.trim();
    if (line != "") {
      Serial.println(line);
    }
  }
  Serial.println("Recorded");
  file.close();
}

This function will keep reading from the file untill it has nothing more i.e till the end of file.

5. Next, we update the setup function which is the function to be executed for the programming of the Arduino board. Here, we call our defined functions according to our need logical need.

void setup() {
  Serial.begin(baudRate);

  pinMode(chipSelect, OUTPUT);

  if (initializeSDCard()) {
    File file = openTheFileFromSDCard(fileName);   
    if (file) {
      readFromSDCardToSerialOutputLineByLine(file);
    }
  }
}

Here, we initialize the serial communication at 9600 bits per second (baud rate), specify the pin mode which is the chip select pin in our case.

6. We leave the loop( ) function module as it is, as we do not need any iterative routine which runs over and over while programming our Arduino.

We are good to go now. Connect the Arduino to the desktop, compile the code and upload it to the circuit board.

Once programmed, we can get the output of the data transmission on the serial monitor in the following way:

Note – In the picture, the dataset name is ‘k24bit’.

Hope this blog adds value to your software development skills.

References:

  1. https://www.hackerearth.com/blog/developers/arduino-programming-for-beginners/
  2. https://youtu.be/sS_oW81NweI
  3. https://www.arduino.cc/en/main/software 

Tags: FOSSASIA, GSOC19, Arduino, Neurolab, Programming, Hardware

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