Using my headphones with my computer is frustrating. Whenever I want to use my headphones, I have to move my computer so I can access the back panel, unplug my computer speakers, and plug-in my headphones. Okay, maybe it isn’t that difficult, but it should be easier. How about a device that allows you to select between headphones or computer speakers?
After some careful thought, I realized such a device could be implemented using three 3.5mm jacks and one dual-pole dual-throw (DPDT) switch (see the schematic below).
As you can see, the DPDT switch simply selects whether the input is connected to the headphones or the computer speakers.
A similar device can be implemented using two dual-pole single-throw (DPST) switches. This would allow the user to select headphones, computer speakers, or both. A much more sophisticated implementation might include operational amplifiers allowing the user to adjust the gain on each output.