Basic Electronics for Beginners: ESP8266 IoT Data Logger: SD Card & ThingSpeak

1. Introduction

Monitoring environmental conditions like temperature and humidity is essential in modern applications such as smart homes, agriculture, weather stations, and industrial automation.

In this advanced IoT project, this is a complete monitoring and data logging system using:

ESP8266 NodeMCU (WiFi-enabled controller)
DHT22 (high accuracy sensor)
16x2 I2C LCD display (minimal wiring)
SD card module (local storage)
Cloud platform for remote monitoring

The system continuously reads data, displays it on the LCD, stores it in an SD card, and uploads it to the cloud for real-time monitoring from anywhere.

This project is an advanced IoT version of temperature and humidity monitoring.

Unlike basic Arduino projects, the ESP8266 allows wireless data transmission and cloud storage, enabling real-time monitoring from anywhere.

If you are a beginner, start with the basic version here:

https://simplebasicelectronics.blogspot.com/2026/04/arduino-temperature-humidity-dht22-lcd.html

2. Components

ESP8266 NodeMCU
DHT22
16x2 LCD with I2C module
SD Card Module
Micro SD Card (FAT32 formatted)
10kΩ Resistor
Breadboard
Jumper Wires
USB Cable

3. Circuit and Connections

Circuit Diagram

🔌 Pin Connections

🌡️ DHT22 Connections

DHT22 Pin	ESP8266
VCC	3.3V
GND	GND
DATA	D4 (GPIO2)

👉 Use 10kΩ resistor between VCC and DATA

📟 I2C LCD Connections

LCD Pin	ESP8266
VCC	3.3V
GND	GND
SDA	D2 (GPIO4)
SCL	D1 (GPIO5)

💾 SD Card Module Connections (SPI)

SD Module	ESP8266
VCC	3.3V ⚠️
GND	GND
CS	D8 (GPIO15)
SCK	D5 (GPIO14)
MOSI	D7 (GPIO13)
MISO	D6 (GPIO12)

4. Detailed Step By Step Circuit Working

The DHT22 sensor measures temperature and humidity.
ESP8266 reads sensor data every cycle.
Data is displayed on the LCD screen.
Data is saved in SD card as a text file.
ESP8266 connects to WiFi network.
Data is sent to cloud using API request.
Cloud stores data and displays graphs.

👉 Even if WiFi fails, SD card continues logging (very important feature)

5. Cloud Setup (ThingSpeak – Full Details)

Platform used:
👉 ThingSpeak

🪜 Step 1: Create Account

Open https://thingspeak.com
Sign up → Verify email → Login

🪜 Step 2: Create Channel

Click New Channel

Fill:

Name: DHT22 Data Logger
Field 1: Temperature
Field 2: Humidity

✔ Enable both fields
✔ Click Save

🪜 Step 3: Get API Key

Go to API Keys tab
Copy Write API Key

📊 Output

6. Libraries to be Included


#include <ESP8266WiFi.h>
#include <SPI.h>
#include <SD.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include "DHT.h"

7. Code


#include <ESP8266WiFi.h>
#include <SPI.h>
#include <SD.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include "DHT.h"

#define DHTPIN D4
#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);
LiquidCrystal_I2C lcd(0x27, 16, 2);

const char* ssid = "YOUR_WIFI_NAME";
const char* password = "YOUR_WIFI_PASSWORD";

String apiKey = "YOUR_WRITE_API_KEY";
const char* server = "api.thingspeak.com";

WiFiClient client;

void setup() {
  Serial.begin(115200);

  lcd.init();
  lcd.backlight();
  lcd.print("System Starting");

  dht.begin();

  if (!SD.begin(D8)) {
    lcd.clear();
    lcd.print("SD Failed");
    while(1);
  }

  lcd.clear();
  lcd.print("SD OK");

  WiFi.begin(ssid, password);
  lcd.setCursor(0,1);
  lcd.print("Connecting WiFi");

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
  }

  lcd.clear();
  lcd.print("WiFi Connected");
  delay(2000);
}

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

  if (isnan(temp) || isnan(hum)) {
    lcd.clear();
    lcd.print("Sensor Error");
    return;
  }

  // LCD Display
  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("Temp:");
  lcd.print(temp);
  lcd.print("C");

  lcd.setCursor(0,1);
  lcd.print("Hum:");
  lcd.print(hum);
  lcd.print("%");

  // SD Card Logging
  File file = SD.open("data.txt", FILE_WRITE);
  if (file) {
    file.print("Temp=");
    file.print(temp);
    file.print(", Hum=");
    file.println(hum);
    file.close();
  }

  // ThingSpeak Upload
  if (client.connect(server, 80)) {
    String url = "/update?api_key=" + apiKey +
                 "&field1=" + String(temp) +
                 "&field2=" + String(hum);

    client.print("GET " + url + " HTTP/1.1\r\n" +
                 "Host: " + server + "\r\n" +
                 "Connection: close\r\n\r\n");
  }

  client.stop();

  delay(15000);
}

8. Detailed Step By Step Code Working

ESP8266WiFi.h → WiFi connection
DHT.h → Sensor reading
LiquidCrystal_I2C.h → LCD display
SD.h → SD card storage
client.connect() → Sends data to cloud
delay(15000) → Required by ThingSpeak

9. Tips

Use 3.3V supply only
Format SD card as FAT32
Keep delay ≥ 15 seconds
Use DHT22 for better accuracy
Check LCD address (0x27 or 0x3F)

10. Uses

Weather Monitoring Systems
Smart Agriculture
Industrial Data Logging
IoT Projects
Research Applications

11. Conclusion

This project demonstrates a complete IoT data logging system using ESP8266, combining real-time display, local storage, and cloud monitoring. It ensures reliability, accuracy, and remote accessibility.

12. ⚠️ Common Mistakes (VERY IMPORTANT)

❌ Wrong API Key → no cloud data
❌ No delay → ThingSpeak rejects data (min 15 sec required)
❌ SD card not initialized → logging fails
❌ Using 5V directly on ESP8266 → damage

Note: You can check the below link for basic version of "Temperature and Humidity Monitoring"

https://simplebasicelectronics.blogspot.com/2026/04/arduino-temperature-humidity-dht22-lcd.html