I recently needed to connect an ESP8266 board up to an audio control and processing board I was working on. And as you can guess the noise was horrendous. Kind of like when you leave your mobile phone near a radio and someone calls you. Pop, pop, crackle, pop pop...
So, some filtering was in order. In the end I came up with this circuit:
The values can probably be refined somewhat, but I just used components I had lying around.
The important thing to remember here is that the audio circuit is the "master" as far as power is concerned. The ESP8266 draws its digital power from the audio power supply, not the other way around.
Why? It's quite simple: it's easier to "block" the noise from the digital from getting back up the chain than it is to clean up a noisy power supply for audio use.
And the results? I occasionally hear a very quiet deep pop, but the noise has now as good as gone.
I have just designed this as a small PCB and I'm going to list them in the shop for sale. Watch this space: [ ]
I have just received the first of my prototypes for this filter circuit, and it works beautifully. Better than the original design.