I designed and build this because my financé kept telling me how difficult it is to keep the noise levels down in a classroom fol of children. So I wanted to see if the kids had a visual indicator that the noise exceeded acceptable levels they would self regulate the noise they make. And if not it would give me a fun project to build anyway. I wanted to make it aesthetically pleasing and after a little bit of research decided to make it look like a traffic light. It's a basic design and easy to make with some basic tools and a 3d printer.
The functionality is very similar to that of a VU meter. It uses a microphone to listen to the ambient audio and when it surpasses a particular threshold it will light either the yellow or red LED. A slight delay will prevent it from jumping around too much and causing a distraction. Two potentiometers allow you to adjust the sensitivity of the microphone and the delay how long a LED should stay on for. The construction is fairly basic.