Tuesday, 10 July 2012

Project: Headphone & Speaker Selector

Choice. With the way and where my computer is set up at the moment, sometimes I use the speakers built into my monitor to listen to music, sometimes it's more appropriate to use my kick arse Sennheiser headphones instead. Being that my computer is set up in the corner of the lounge room, the headphones allow everyone to have their way. The problem is if I want to use the headphones after I've used the monitor speakers, I have get under the desk and unplug cables. This usually results in me hitting my head on the bottom of my desk, and swearing gratuitously. And it's just a mild inconvenience.

So I had the idea of building a small selector with a rocker switch. Everything would stay plugged in neatly to a small box on my desk, and to switch outputs I simply alternate the rocker switch. Seemed simple enough, so I came up with this.


The original concept circuit diagram...before things went horribly wrong.

This all looked great on the screen, seemed logical in my head. Both outputs would have shared left and right channels, and the earth would be switched by a SPDT rocker switch (http://www.jaycar.com.au/productView.asp?ID=SK0991). The logic was that without an earth the inactive output would be exactly that - inactive. Unfortunately this is not how things work in reality, and it resulted in all sorts of unexplainable observations and continuity readings. Basically the rocker switch did not work as desired, and the left channel on both outputs was intermittent to missing altogether. Back to the drawing board.

Further Google Fu-ing revealed someone else that had had the same need for a device like this, and they'd been kind enough to blog about it and post a circuit diagram. Which I shamefully stole and forgot to get the link for crediting (if it's yours, let me know and I shall credit you). It is the same principal, just the opposite - both outputs share their earth, and it is the left and right channels that are switched by the rocker. This meant I needed a DPDT 6 pin switch, which funnily enough Jaycar didn't stock (in rocker form, anyway). Ebay had my back. Basically the unit as before, just twice as many pins.

The circuit I ended up following. Notice how it is basically the total opposite I what I designed.

After waiting about two weeks for my new switch to show up in the mail, I realised the small plastic project box I had initially built my failed design into wasn't actually big enough to handle the new 6p DPDT switch. So I scrounged around....and found the left over box from out ATV2 unit. It's actually a decent box, as far as being excited about cardboard goes. I cut it down so that I had just a short section of the bottom. As an enclosure for the device, the bottom will remain open just for convenience, but it won't be seen unless it's picked up off the desk.

Testing the assembled circuit BEFORE putting it all into it's enclosure. Foresight! FORESIGHT!

And it worked. As you would expect. Which needless to say I'm pretty fucken happy about. One step closer to total automation/death by physical inactivity.

The bottom of the device, showing all inputs/outputs, and the 6p DPDT switch.

The finished product. Like a boss.

And that's it. It's not overly pretty; I mean I could have gone to Jaycar and bought a suitable enclosure. But that means stuffing around drilling holes (I don't have a drill), making a mess, spending more time on it than I can be bothered. And this way uses stuff I just had lying around. Enjoy.

PS: apologies if the formatting in this post looks SUPER shit. For some reason the blogger text editor is being a pain to do simple things today.


  1. Would this work with the audio coming the opposite direction i.e. choosing between two inputs going to one output?

  2. Yes, it certainly would. You basically wire it up backwards to mine. You could even have more than two selectables to the one outlet, provided you can get a DPDT switch with enough pins. Or you could use relays, but then you'd need a power source.