How to Build a Sensor Data Logger with ESP32

What is a Sensor Data Logger and Why Use One?

A Sensor Data Logger is an embedded system designed to monitor, record, and sometimes transmit real-time measurements from sensors over a period of time. These measurements might include temperature, humidity, pressure, voltage, current, or any other physical phenomena depending on the application. Data loggers are essential tools in industrial automation, environmental monitoring, agriculture, logistics, and research.

The ESP32, with its dual-core processor, integrated Wi-Fi/Bluetooth, and extensive GPIO capabilities, offers a cost-effective and flexible platform for building sensor data loggers. Its processing power and connectivity options allow not only for local data logging but also for remote monitoring via cloud platforms or local servers.

Use Cases and Applications of ESP32-Based Sensor Data Loggers

Industrial Monitoring

Monitor machine temperature, vibration, or current consumption in manufacturing environments.

Environmental Monitoring

Track parameters such as air quality, CO2 levels, and ambient temperature/humidity in greenhouses or smart cities.

Agricultural Automation

Log soil moisture, light intensity, and temperature for precision farming applications.

Cold Chain Logistics

Ensure proper storage conditions for pharmaceuticals or perishable goods with GPS-enabled ESP32 modules.

Home Automation & Research

Use it for academic projects or smart home systems that involve time-based data collection.

Integration and Setup: Building Your Sensor Data Logger

Components Required:

ESP32 Development Board
Sensors (e.g., DHT22 for temperature/humidity, MQ135 for air quality, BMP280 for pressure)
MicroSD Card Module (for local storage)
Breadboard and Jumper Wires
Optional: RTC Module (e.g., DS3231) for accurate time stamps
Power Supply (USB or battery)

Wiring Diagram:

Connect sensors to the ESP32 according to their communication protocol:

I2C sensors to GPIO21 (SDA) and GPIO22 (SCL)
Analog sensors to GPIO36 or GPIO39 (ADC capable)
MicroSD module to SPI pins (GPIO23, GPIO19, GPIO18, GPIO5)

Tip: Always ensure voltage compatibility (3.3V logic for ESP32).

Code Overview

Here’s a simplified example using DHT22 and SD card logging:

⚙️

code.ino

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

#define DHTPIN 4
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);

#define CSPIN 5
File dataFile;

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

  if (!SD.begin(CSPIN)) {
    Serial.println("SD card initialization failed!");
    return;
  }

  dataFile = SD.open("/datalog.txt", FILE_WRITE);
  if (dataFile) {
    dataFile.println("Time,Temperature,Humidity");
    dataFile.close();
  }
}

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

  dataFile = SD.open("/datalog.txt", FILE_WRITE);
  if (dataFile) {
    dataFile.print(millis());
    dataFile.print(",");
    dataFile.print(temp);
    dataFile.print(",");
    dataFile.println(hum);
    dataFile.close();
  }

  delay(5000);  // 5 seconds interval
}

Product Features to Consider for Deployment

When designing for real-world usage, enhance your logger with:

Enclosures for outdoor/industrial use
Power optimization using sleep modes
Wi-Fi/GSM modules for remote data push
Edge processing for threshold alerts or event triggers

Conclusion

With the ESP32, building a flexible, cost-efficient Sensor Data Logger is both accessible and scalable. Whether you’re logging data to an SD card for local analysis or pushing it to the cloud for remote visualization, ESP32 offers a powerful foundation. From environmental monitoring to smart factories, this solution empowers engineers and developers to create reliable and application-specific data logging systems.

Ready to build your own? Explore our range of ESP32 Industrial Controllers with built-in RS-485, GSM, and LTE connectivity to take your sensor logger to the next level.