This audio splitter and mixer takes in one input from a bluetooth device, and splits it into two 3.5mm audio jacks

Not only does this device split the single source into two, the user is also able to adjust the treble, mid-range, and bass via dials on the top

I also added in the functionality of bluetooth while all being powered by a common 15V AC to DC cord

I began by testing the circuit above via breadboarding

This test did not account for bluetooth integration or the power source since I used one of the lab power sources to power the op-amps

I tried to match the resistors and capacitors to the design exactly but not all were available in the lab

In the picture above, there are 5 capacitors in parallel. For the final design, I knew that this was not practical, but I just wanted to ensure the success of the circuit that was provided by Texas Instruments.

Once the circuit was built, I began testing by plugging in a portable bluetooth speaker to the output and my laptop to the input

Since my design is an audio splitter, the output heard from the speaker is either the left or right channel (whichever contact I choose to connect from the 3.5mm jack)

I knew that we did not have some of the exact component values called for from the original schematic, so I began testing different resistors and capacitors to ensure that the final audio output was not distorted

As shown in the photo to the right, I planned to include two separate circuits onto the same board

In addition to both circuits I planned to add a bluetooth receiver so that the splitter/mixer could be controlled via any bluetooth device

I also wanted to power this device through one cable instead of multiple power inputs, so I added a voltage regulator for the bluetooth module to be powered from

Another challenge with the design was powering the op-amps. Since they need +/- power, I had to find a separate power source that would be able to perform this conversion

I wanted to keep the enclosure design very simple by only having dials on the top, and the outputs on each side

I decided to resin print the entire design because I thought that the robustness of the resin prints aided in the protection of the circuit

I also had a fairly complicated lid design that would house the potentiometers, so I needed the enclosure to be nearly exact with the dimensions

I wanted to create a board that was very compact, but there were so many individual components that it was difficult to implement all of these in such a small area while only using two layers

After I thought that I had the layout correct, I realized that there was a wire that was connected to the incorrect pin, so I had to redo the schematic and check again to make sure that the design was flawless.

Luckily, this mistake happened before the enclosure was created, so I was able to adjust the design to account for this change

I was slightly worried about the 3.5mm inputs being pulled out of their housings, so I hot glued these to the enclosure

I also hot glued the potentiometers to the lid even though they were already very secure

I began by soldering the PCB together

In order to test this board, I simply connected to the bluetooth module, and then connected the output to my external stereo system

The photo to the left shows the board with some of the potentiometers soldered to it

As you can see at the top of the photo, there is a green and a black cable that are connected to the aux cable leading from the audio out on the board

I would then begin turning each potentiometer to ensure that the direction was correct, and it was adjusting the correct range

I would then mark each of the potentiometers with tape, so that when I placed them into the enclosure, I was sure which one was which