So I'm currently dreaming up my first PCB project! I would like to make a 1/4 audio switcher for my current audio setup (two outputs 1 input)

I'm fairly new to electrical engineering I'm about 3 years in but have a grasp on the basics from a variety of projects. However, I'm am unsure of the viability of this one and I don't know where to look for the correct resources on this.

My Idea is to power some kind of capacitor/battery that can then be stepped up to a voltage that can run a small chip like an ESP32 to handle the interactions. I then want to use Mosfets to switch the signal from one side of the output to the other. I was wondering if it was possible to siphon the initial power from the output of the headphone jack to charge some persistence circuit that will maintain this power; and or trickle charge an onboard battery without interrupting the audio stream after a while.

My main concern is that there wouldn't be enough throughput to start to process but I have no idea.

From my initial googles, it says the standard output of a headphone jack is about 100mW!

I'm looking to see if anyone can point me in the right direction for this project! The ESP32 has a deep sleep mode the minimizes power consumption and Im under the impression that this might be possible just due to the fact that driving headphones must take some power. Worst case ill just add a USB connection but I'd rather not go that route.

If anyone can help it would be super appreciated I feel like this would be a great way to expand my knowledge of electrical engineering!

  • \$\begingroup\$ siphon the initial power ... what is initial power? \$\endgroup\$ – jsotola Apr 7 at 0:54
  • \$\begingroup\$ by that, I mean the power that would normally control and power the speakers in the headphones \$\endgroup\$ – Echo Apr 7 at 0:55
  • \$\begingroup\$ that would be the audio signal ... it is continuous, not "initial" \$\endgroup\$ – jsotola Apr 7 at 1:00
  • \$\begingroup\$ yes! that is correct but im trying to have it use as little as possible to avoid interference with the audio quality and or stop after an adequate charge is made. Also, I'm capable of writing a web app that could blast the audio for like a minute on startup if something like that is necessary \$\endgroup\$ – Echo Apr 7 at 1:08
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    \$\begingroup\$ USB seems like the better choice. \$\endgroup\$ – Tony Stewart EE75 Apr 7 at 1:41

In principle it could be feasible if you are crazy micropower everything and using techniques like energy harvesting. However there is one tiny little issue:

You will inject noise in the audio path

Every time you suck a little power, that would create a voltage across the wire that will be read as audio signal by the receiver. So the result would be probably some interference like a cell phone in the tv audio.


It can be done but it doesn't sound like a great idea. Not only to you have the issue of degrading the audio signal, but also when the signal is quiet - no power. What happens then? Maybe, just maybe, you could design around it (make your controller go in sleep, design your switches so that they stay switched with only the tiniest gate charge on a FET) but it's likely to be glitchy and - in the end, what's the point?


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