DIY Arduino Data Logger: Log Temperature & Humidity to an SD Card

Ever wanted to track environmental conditions in your workshop, greenhouse, or 3D printer enclosure? With a few basic components, you can create your own temperature and humidity logger that saves data to a microSD card for later analysis—no Wi-Fi required.

What You’ll Need

• Arduino Uno (or compatible board)

• DHT11 or DHT22 temperature & humidity sensor

• Micro SD Card Module (SPI)

• microSD card (formatted FAT32)

• Jumper wires

• 5V power source (USB or adapter)

• RTC could be a nice addition for timestamps!

Wiring Guide

🔹 DHT Sensor (Connected to Digital Pins)

DHT Pin	Arduino Pin
VCC	5V
GND	GND
DATA	D6
(N/C)	—

Note: If your DHT sensor has only 3 pins, it will be VCC, GND, and DATA.

SD Card Module (SPI Pins)

SD Module Pin	Arduino Pin
GND	GND
VCC	5V
MISO	D12
MOSI	D11
SCK	D13
CS (SS)	D10

Arduino Code

Install these libraries first:

• DHT sensor library by Adafruit

• SD library (built-in to Arduino IDE)

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

#define DHTPIN 6
#define DHTTYPE DHT11
#define CSPIN 10

DHT dht(DHTPIN, DHTTYPE);
File logFile;

void setup() {
  Serial.begin(9600);
  dht.begin();

  if (!SD.begin(CSPIN)) {
    Serial.println("SD card failed or not present.");
    return;
  }

  logFile = SD.open("datalog.txt", FILE_WRITE);
  if (logFile) {
    logFile.println("Temp(C),Humidity(%)");
    logFile.close();
  }
}

void loop() {
  float temp = dht.readTemperature();
  float hum = dht.readHumidity();

  if (isnan(temp) || isnan(hum)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  logFile = SD.open("datalog.txt", FILE_WRITE);
  if (logFile) {
    logFile.print(temp);
    logFile.print(",");
    logFile.println(hum);
    logFile.close();
    Serial.println("Data logged.");
  }

  delay(5000); // Log every 5 seconds
}

Reading Your Data

After the logging session, remove the SD card and plug it into your PC. Open datalog.txt with Excel, Notepad, or any CSV viewer to see your timestamp-free log of temperature and humidity readings.

Use Cases

• Science experiments

• Greenhouse monitoring

• 3D printer enclosure tracking

• Graphing environmental changes over time

  
  

Wrap-Up

The Arduino + DHT11 + SD Card combo is a simple yet powerful way to start logging real-world data. Want to upgrade it? Add an RTC (Real-Time Clock) module for timestamped logs or Bluetooth to send live data to your phone.

Looking for the hardware? We stock SD card modules, DHT sensors, and jumper kits. Drop us a DM or check our link in bio.

Let me know if you'd like this formatted for your website, or if you want a version with timestamps or real-time graphing via serial!