Arduino Temperature Control - Adjust Fan Speed based on Temperature

This automated temperature control system operates by continuously monitoring ambient environmental conditions and adjusting cooling output dynamically using an Arduino Uno. At the heart of the sensing subsystem is the DHT11 sensor module, which periodically measures the surrounding air temperature and transmits digital data back to the microcontroller. The Arduino Uno processes this incoming temperature data via its digital input pins using a custom sketch written in the Arduino IDE. When the measured temperature crosses predefined thresholds, the microcontroller alters its output using Pulse Width Modulation (PWM). Because the Arduino's digital pins cannot directly supply the high current required to drive an inductive load like a DC fan, a 2N2222 NPN transistor acts as a solid-state electronic switch. The PWM signal from the Arduino feeds through a 1K resistor into the base of the 2N2222 transistor, safely controlling the larger collector-emitter current flowing from the 9-volt battery through the DC fan. Simultaneously, the system updates a 16x2 LCD display to provide real-time visual feedback of the current temperature readings and corresponding fan operation status. This closed-loop interaction between sensor input, microcontroller computation, transistor-based power switching, and visual telemetry creates a fully automated, responsive cooling loop powered independently by the 9-volt source.