The device I want to make is simple to describe: a big red lightbulb, connected to the AC 110 / 220 V, stays dark when it's quiet in the room, starts lighting up somewhat if there's a moderate level of noise, glows brightly when there's a lot of noise. When the room goes quiet again, the bulb turns dark.
Basically, a visual cue that you're making too much noise and you need to keep quiet.
The device doesn't need any hysteresis or a lot of inertia - it's fine if it tracks the instant level of noise quickly. Of course this is easy to control via a low pass filter or something.
Back when I was a wee lad in school, I knew how to make the classic circuit with a triac that could control the AC bulb with a small DC signal. But that works with incandescent bulbs. I am less sure about them newfangled LED bulbs - do they work well with the chopped up AC sine curve that comes out of the triac? So that's issue number one.
The other part of the circuit should capture the signal from a microphone, amplify it, and inject it via an optocoupler into the AC controller. I'm pretty sure I can figure this one myself (could be as simple as an opamp and a few passive components), but anyway if you have a better idea (like if there's a dedicated IC or something) then I'd be happy to learn from you. The thing here is to introduce a logarithmic scale, to mimic the sensitivity of the human ear - other than that it should be pretty basic. I remember there was a trick with a FET in the loop that would stay pretty close to a logarithmic curve.
Perhaps there's an IC that does all this already? (except the pure AC stuff)
Any suggestion is appreciated. Thanks!