Build a 3.5mm Audio Switch

audio mux p2

I moved to Berlin a few months ago to start working as Lead Electronics Engineer at UNU Motors. As soon as I found my own place (after spending three months apartment hunting), I decided to buy a good audio monitor, so I could listen to music and watch videos with a decent audio quality. My choice was a BX5 M-Audio audio monitor, great speaker at a very good price. The only annoying thing is that every time I wanted to listen music from my computer, I had to take the P2 plug from the RaspberryPi (running OSMC) and connect to my mac, and vice versa… To fix this problem, I decided to make a small PCB where I can plug everything together and then flip a switch to toggle inputs.

I had a few 3PDT switches at home, so I decided to use them on the board, but I could have also used a DPDT switch by connecting all the grounds together. After ordering the PCB from OSH Park and testing it, I decided to share the project with the world, maybe it will be useful for someone out there. The board was designing using Eagle Cad and you can download the project clicking here or visiting the GIT repository.

The circuit

3pdt switch
The 3PDT switch has 9 pins, left, right and ground for each connector. Following the positions from the image above I created the board that will switch all three connections from two different inputs. The result is the PCB below.

audio mux p2 PCB
The board I sent to OSH Park had a small problem, the drill size was a bit too small and the switch didn’t fit in the holes, so I had to solder them on top. It still worked, but didn’t look as good as I wanted. The files I am sharing now already have the hole size fixed, so you don’t need to worry about that anymore.

Parts

You can find the audio sockets and the 3PDT switch on eBay. The PCB you can Order from OSHPark.

In a near future I will build a 3D Printed case for the board, once that’s done I will share it here!

More photos

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10 Comments Add yours
  1. Does this work in the opposite direction? For instance, can you plug a source into one side, and separate monitors into the side-by-side 3.5 mm jacks and use the switch to determine which output you are using?

  2. I made one of these from your board, with the intention of switching one source between headphones/speakers, but I get a lot of interference on the speakers. Have you had an issue with that?

    1. Can you share a picture?
      The only problem with the board is that it makes a click sound when I switch. Also if I select a side where the cable is not plugged I can hear a noise. Other than that, it’s all good!

  3. Great project! Nice PCB, though as an audio person it should be a shielded (groundable) container / enclosure. As to the clicks, they should reduce “appreciably” with the use of fully wired grounds (no switching the commons, just solder them across at the switch) and the use of a “Make before Break” switch. When switched, the contacts in use remain closed until the motion of the switch blades closes into its new circuit position, at which point the old circuit opens. There is a selection of body and duty types. The momentary halving of the circuit impedance effectively attenuates any clicks that might have been caused by open circuit switching.

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