AJAX with ESP8266: Dynamic Web Page Update Without Reloading

This project creates a local web server using an ESP8266 NodeMCU to monitor environmental data and control hardware in real time without requiring full page reloads. At the heart of the system is the NodeMCU, which connects to a local Wi-Fi network and hosts a lightweight HTML webpage. The LM35 temperature sensor is connected to an analog pin on the NodeMCU, where it measures ambient temperature and outputs a continuous analog voltage proportional to the thermal conditions. When a client visits the web page, JavaScript running inside the browser periodically sends asynchronous HTTP requests—known as AJAX requests—to the ESP8266. Upon receiving these background requests, the microcontroller reads the current analog value from the LM35, processes it into readable temperature data, and returns only the updated values to the browser, which updates the interface dynamically. Simultaneously, the webpage includes interactive controls that allow a user to toggle an external LED connected to a digital pin. When a button is clicked, an asynchronous command is sent back to the ESP8266, which instantly changes the state of the digital output pin to turn the LED on or off. By using a 150-ohm current-limiting resistor in series with the LED, the circuit safely protects the semiconductor from excessive current drawn from the NodeMCU's digital pins. The breadboard and jumper wires provide a reliable, solderless way to interconnect the NodeMCU, sensor, resistor, and LED into a cohesive working prototype.