Air cleaners are indispensable appliances in shop environments. Fine sawdust in the air can, for example, cause a variety of respiratory ailments in woodworkers. Even if the tool itself has a vacuum collection system, dust will fill the air. But air cleaners are noisy and require quite a lot of power, which means that most shop owners and workers don’t want to leave them running all day. To ensure that their air cleaner only runs when necessary, Atomic Dairy built this sound-reactive activation system for their air cleaner.

The system activates the air cleaner when two conditions are met: the shop lights are on and the sound levels exceed a set value for a set amount of time. Those conditions ensure that the system doesn’t activate when no one is in the shop or when a momentary loud noise occurs. When the conditions are met, the system turns on the air cleaner for 30 minutes. A readout displays the amount of time left until the air cleaner turns off and a Larson Scanner-style row of LEDs provides a visual indication. The components reside in a sealed enclosure, so that sawdust doesn’t collect and cause heat issues.

An Arduino board controls the whole system. It listens to the environment through a simple microphone and looks for voltage spikes that correspond to loud noises. A photodiode lets the Arduino know if the shop lights are on or off. It activates the massive air cleaner fan through a relay module. The remaining time readout appears on a pair of four-digit, seven-segment display modules that connect to the Arduino via SPI. There is also a button that lets people in the shop manually activate or deactivate the air cleaner.