First off, we need to get together our supplies.
You will need these tools:
"Helping Hand" holder
Hot glue gun
Rotary tool with cone grinding bit
Needle Nose Pliers
The supplies are as follows:
3x female 3.5mm stereo panel mount audio jacks
1x DPDT toggle switch
3 male to male 3.5mm cables, or whatever 3.5mm cables you plan on using (male to female, male to RCA, etc)
and, of course, LEGOS!
Strip about 1/4" to 1/2" of each end of the wire lengths.
Put the stripped bit of wire through the proper hole, and bend it over on itself using the needle nose pliers or your fingers.
To save yourself the frustration, use the Helping Hands to hold the jack and wires in place while you solder the wires to the connections.
For my connections, I used green wire for the ground, red wire for the right connection, and black for the left connection.
I used these 2x2 right angle pieces to mount the jacks; seemed like the logical choice, since they already have a hole in the middle. However, the hole is not big enough for the audio jack to fit through, so I used a rotary tool with a cone grinding bit to open the hole up a little bit. I also used it to carefully clean off the surfaces after I got the hole to correct size.
On each of the audio jacks is a ring/nut that goes around the threaded port. Remove this ring using your fingers or the needle nose pliers (they can be a little tough to start without the pliers).
Put the port through the hole you created in the Lego piece.
Thread the ring onto the port, and tighten using the needle nose pliers.
If you made the hole just big enough to get the port through it, the ring should be sufficient to hold the jack. If it's loose, you can use a little hot glue to secure it if necessary.
The connections on a DPDT switch are set up in 2x6 configuration. For the purposes of this project, we can think of the 2 connections in the middle are the main output, and each of the 2 connects on either side are like audio channel 1 and 2. Each set of connections is broken into right and left channels.
Whichever way you flip the switch, it allows current from the terminals on the other side. You flip it to the left (like in the picture), and it allows current from the right terminals to pass to the middle terminals, and vice versa. I didn't realize that until I got everything working, but I was able to swap the Legos around to make it work the way I wanted it to.
I started with the middle connections, since I figured it would be more difficult to get to them if I did one or both of the outside connections first.
Like with the audio jacks, insert the exposed ends of the wires through the holes and bend them back on themselves using needle nose pliers.
Solder the wires to each of the terminals. Make sure there is not solder bridging the gap (it'd be pretty hard to do on the big switch I used, but it could happen with a smaller switch).
Repeat those steps with the outside terminals, making sure that all of the right wires are in a row, and all of the left wires are in a row.
Plug an audio source into the channel 1 jack, and another into the channel 2 jack. Plug in speakers or headphones into the master out. Press play on both of the sources, and listen to make sure stereo audio is coming through. Use this setup to troubleshoot the solder connections.
Be creative! You could make a unicorn, or a robot, or a little house. Whatever suits your fancy!
Additionally, you can mount the toggle switch into a flat Lego piece. I chose not to do that, since it wouldn't really work with the design I was putting together.
If you took the ground wires apart while you were building your creation, twist them back together. Solder them all together, and hot glue them if you wish.
I ended up hot gluing the switch in place, as well. You may not need to do this, since your creation will probably be different than mine.
Congratulations! You should now have a working 3.5mm audio switch that you can be proud of :)
If you wish, you can always reverse the way it works: have audio from one source come in, and output to a couple separate sources.
I hope you have found this tutorial helpful :)