Arduino Data Logger

Circuit Description

This Arduino-based data logger system records sensor data to an SD card at regular intervals. The circuit features temperature and humidity monitoring via a DHT22 sensor, real-time clock functionality for accurate timestamping, and SD card storage for data retention. This system is ideal for environmental monitoring, science experiments, or any application requiring long-term data collection.

How It Works

The Arduino Uno forms the core of the system, reading the temperature and humidity values from the DHT22 sensor. The DS3231 RTC module provides accurate time and date information for each reading. Data is formatted as CSV (comma-separated values) and written to the SD card through the SD card module. The system operates on battery power with a voltage regulator to ensure stable operation.

Circuit Schematic

Arduino Code

#include <SPI.h>
#include <SD.h>
#include <Wire.h>
#include <RTClib.h>
#include <DHT.h>

#define DHTPIN 2      // DHT22 data pin
#define DHTTYPE DHT22 // DHT sensor type
#define SDPIN 10      // SD card CS pin

DHT dht(DHTPIN, DHTTYPE);
RTC_DS3231 rtc;
File dataFile;

void setup() {
  Serial.begin(9600);
  
  // Initialize DHT sensor
  dht.begin();
  
  // Initialize RTC
  if (!rtc.begin()) {
    Serial.println("Couldn't find RTC");
    while (1);
  }
  
  // Set RTC time if needed (uncomment and set once)
  // rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  
  // Initialize SD card
  Serial.print("Initializing SD card...");
  if (!SD.begin(SDPIN)) {
    Serial.println("initialization failed!");
    while (1);
  }
  Serial.println("initialization done.");
  
  // Create or open data file and write header
  dataFile = SD.open("datalog.csv", FILE_WRITE);
  if (dataFile) {
    if (dataFile.size() == 0) {
      dataFile.println("Date,Time,Temperature (C),Humidity (%)");
    }
    dataFile.close();
  }
}

void loop() {
  // Get current time
  DateTime now = rtc.now();
  
  // Read temperature and humidity
  float temp = dht.readTemperature();
  float hum = dht.readHumidity();
  
  // Check if reading was successful
  if (isnan(temp) || isnan(hum)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }
  
  // Format date and time strings
  char dateStr[11];
  sprintf(dateStr, "%04d/%02d/%02d", now.year(), now.month(), now.day());
  
  char timeStr[9];
  sprintf(timeStr, "%02d:%02d:%02d", now.hour(), now.minute(), now.second());
  
  // Open file and write data
  dataFile = SD.open("datalog.csv", FILE_WRITE);
  if (dataFile) {
    dataFile.print(dateStr);
    dataFile.print(",");
    dataFile.print(timeStr);
    dataFile.print(",");
    dataFile.print(temp);
    dataFile.print(",");
    dataFile.println(hum);
    dataFile.close();
    
    // Print to serial monitor
    Serial.print(dateStr);
    Serial.print(" ");
    Serial.print(timeStr);
    Serial.print(" - Temp: ");
    Serial.print(temp);
    Serial.print("°C, Humidity: ");
    Serial.print(hum);
    Serial.println("%");
  } else {
    Serial.println("Error opening datalog.csv");
  }
  
  // Wait 5 minutes before next reading
  delay(300000); // 5 minutes in milliseconds
}