Introduction: Dual Input Audio Switching Circuit

About: I'm a mechanical and mechatronics engineer with a PhD in robotics. In my spare time I love playing soccer and tinkering with electronics!

Have you ever had the issue of having one speaker system and multiple inputs that require you to plug and unplug your audio leads each time you want to listen to one source? Well, I've got a solution for you! This Instructable is about making a very simple 3.5mm stereo audio switching circuit. All you need is a switch, a few audio sockets, an enclosure of some sort and some wires. In this Instructable, I've made a switching circuit for 2 inputs and one output, but this can easily be expanded to several inputs and one output by swapping out the switch and using more audio sockets. Let's get to it!

Step 1: Get Your Parts Together

Here's what you're going to need for this project:

Soldering iron
Wire stripper/side cutters
Hobby knife
Drill and drill bits

3x 3.5mm stereo audio sockets

1x DPDT switch
1x Sugru packet
1x small plastic enclosure
Small amount of wire
Small amount of glue

Step 2: Prepare the Enclosure

Here we are going to drill out some holes so you can mount the audio sockets and the switch. Position the holes where you desire, I put the two audio inputs on one face and the audio output on the opposite face of the enclosure. I put the switch on the front face of the enclosure. Drill appropriate sized holes for the 3 audio sockets. The switch is a bit tricky to attach to the enclosure and I didn't do a very neat job of this... I first drilled a hole at the approximate centre of where I wanted to position the switch and then I ended up using the tip of the soldering iron to melt away the rest of the material. Unfortunately when I did this, it melted away a lot more material than I wanted and I was left with a hole that was bigger than the switch. To avoid this, I recommend marking out the switch beforehand and melting the plastic away gradually. Use a hobby knife to trim the excess plastic and make the face of the enclosure smooth.

Step 3: Wire Up the Switch and Audio Sockets

I recommend soldering wires to the switch first and then soldering the other ends to the audio sockets. The switch I chose was a DPDT switch meaning it has 3 columns * 2 rows of pins. The two rows are for the left and right channels and the three columns are for your inputs and output. Keep in mind that the centre column pins on the slider switch are the output pins and the others are for your inputs. Make sure you measure out the wires so that there is plenty of length to reach from the space in the enclosure for the audio socket to the switch. What you're soldering here are the left and right channels only to the switch. Colour coding the wires helps to make sure you connect the correct wires to the correct pin on the audio socket. Solder all the ground pins of the audio sockets together via black wires and solder the left and right channels to the switch.

Step 4: Fit the Audio Sockets and Switch Into the Enclosure

Mount your audio sockets to the enclosure by unscrewing the small nut that comes attached with the socket. Push the socket through the hole you have drilled and reattach the nut to hold the socket in place. Remember to position the inputs on one side of the enclosure and the output on the opposite side. Position the switch in place and use some glue to attach it to the enclosure, be careful to avoid getting glue in the switch mechanism though, otherwise your switch won't work!

Step 5: Close the Gaps With Some Sugru

The gaps I mentioned in step 2 can be closed up with a little bit of sugru. You can also use sugru to mount the switch to the enclosure in the previous step. Again, just make sure that none of it gets inside the switching mechanism otherwise you'll have to get a new switch to solder in.

Step 6: Close the Box and Give It a Test!

The enclosure I bought had a nice lid with some screws included. Simply screw the lid onto the box in this step. Connect your inputs and output and give the circuit a test!

Once you've connected your inputs and output, play with the switch and see which source belongs to which side of the switch. After you've figured this out, use some labels to mark the enclosure so you know which input is which.

So that's it, you're all done and ready to enjoy hassle free listening at the flick of a switch!