Make Your Own Automatic Exhaust Fan | Full Electronics Project

The Automatic Exhaust Fan project operates by continuously monitoring air quality using an MQ2 gas sensor, which detects smoke and combustible gases. Power is supplied reliably to the circuit through a 7805 voltage regulator, ensuring the sensitive digital components receive a stable 5V supply. The heart of the system is an ATtiny85A microcontroller programmed via the Arduino IDE, which reads the analog or digital output signal from the MQ2 sensor, adjusted by a potentiometer to set the detection sensitivity threshold. When the sensor detects smoke levels exceeding the set point, the ATtiny85A changes its output state to trigger a BC547 NPN transistor. This transistor acts as a current amplifier, allowing the low-current microcontroller pin to drive the coil of a 5V single changeover relay. As the relay energizes, its switch closes to complete the circuit for an external exhaust fan. Simultaneously, a common-cathode bi-colour LED provides a visual status indicator—typically glowing one color during normal standby operation and switching to another color when smoke is actively detected and the fan is activated. A pushbutton switch is also included for manual control or resetting functions, while various supporting resistors and capacitors ensure stable signal filtering and current limiting throughout the board.