Deej Sound Mixer

Howdy Y'all

My name is David Nemec, I am a Senior engineering student at Texas A&M University pursuing a degree in Manufacturing and Mechanical Engineering Technology or MMET. For the Digital Fabrication: Student Design Challenge, I wanted to use as many different digital fabrication methods as possible. I have wanted a sound mixer for my PC setup for a long time and recently ran into a DEEJ project on GitHub. Deej is an open-source hardware volume mixer that allows for you to control different applications' volumes using sliding or rotating potentiometers. If you commonly find yourself adjusting your game volume, discord, media player, and browser this project is for you.

The plan for my Deej is to design an aluminum plate for the rotary potentiometers to mount to which will go with a 3d printed case. To mark what each potentiometer does I will laser engrave the application onto the plate.

For those who do not have access to a CNC Mill/Router, there are many fully 3D printed models that can be found via the GitHub page or in this Thingiverse collection.

Materials Used

• Scrap 0.25in aluminum plate
• 5 B10K Rotary Potentiometers
• 5 Knobs for Rotary Potentiometers
• Arduino Pro Micro Controller
• Wire
• Solder
• Spray Paint

Equipment Used

• CNC Router - Local Maker-space
• Drill or Drill Press
• 3D Printer
• Laser Cutter/Engraver
• Soldering Iron
• Painting Booth
• 
  

Digital Fabrication, or more commonly referred to as CNC manufacturing. There are two common schools of manufacturing, additive and subtractive. Additive manufacturing removes material such as in Milling or Turning, this is the more traditional manufacturing method that uses shear force to remove material. Additive manufacturing is most commonly used to refer to 3D printing and allows for rapid prototyping and more recently, has allowed the common man to create their own parts at home. Subtractive has the advantage of using any material imaginable to create almost anything, most commonly limited only by workholding and the number of axis on your machine. Additive manufacturing has the advantages of not needing any workholding, using low-cost machines, having almost no geometric constraints, and the ability to iterate very quickly. Disadvantages include the more limited material choice and poor mechanical properties of most commonly used materials.

The first step in the process is designing a case for your components. I decided to use rotary potentiometers to reduce the overall footprint of the mixer. To make my life easier I first found a model of a similar potentiometer to my own on GrabCad, using premade files allows for more rapid development of your design. I then referenced my own potentiometer and measured the critical dimensions using a caliper. This allowed me to size the holes in the plate correctly. The entire design is very simple and a live link can be found here.

To add some weight to the case I decided to use aluminum to make the mounting plate. To manufacture the plate I used the CNC router at a local maker space. But before using the CNC I first had to program it in FusionCAM. For a more in-depth description of CAM check out my previous project making a Vice Handel here.

I first created a facing tool path using a 0.25" endmill to remove 0.125" from the aluminum plate, bringing it to the final dimension of 0.125" thick. Next switching to a 0.125" endmill, I perform a helical bore to cut out the holes for the potentiometers, and finally a slotting toolpath to cut out the profile.

Since the CNC router at the makerspace did not have any workholding available I drilled holes into the stock and then screwed it into the MDF. My speeds and feeds were too aggressive for cutting without coolant and caused the 0.125" endmill to become clogged with chips, this led to the endmill to rub more than it did cut, leaving a horrible finish.

To clean up, I took it back to my workshop and cleaned it up on a belt sander, and then used a drill press and chamfer tool to clean the holes. I then sanded the whole plate to create a uniform surface finish

For the case, I wanted to try to use my new SLA 3D printer, also known as Stereolithography. In this 3D printing method, a photopolymer resin is exposed to high-intensity UV light which cures the resin. Layer by layer the print is built up. The major advantage over FDM 3D printing is the high level of detail that is achievable. I had to split the case into two pieces to fit it onto my 3D printer and then glued the two halves together using CA glue.

I went through multiple tries to get the resin print to come out well, but I am new to resin printing so I would suggest looking up videos on how to set up prints in the event that you want to print it as well.

I first test fit the potentiometers into the plate and everything went together perfectly. Using the schematic from the GitHub I wired up the potentiometers with the left legs in parallel with each other and connected to the GRD pin on a Pro Micro Controller. The right legs were then soldered in parallel and connected to the VCC output. The center leg of each potentiometer were then each connected to an analog pin on the Pro Micro.

The initial plan was to anodize the mounting plate, however, my attempts to anodize failed, and instead I resorted to painting the plate. After a small amount of sanding, I used spray paint to give a nice finish to the plate and case using multiple light coats of paint.

Using the laser cutter at my work I engraved the painted surface with different application logos and tick marks for the volume knobs. Using AutoCAD I designed the pattern and using the PLOT command sent it to our laser cutter. Unfortunately, I do not have the AutoCAD file to distribute but it can be done in Fusion360 or Photoshop rather easily.

To hold down the Pro Micro I simply hot-glued it onto the bottom of the case and the plate simply slots into the case and is a friction fit. There is space to add heat set inserts if FDM printing was used to make the case. Everything should slot into place and there should be minimal wire mess inside the case.

To upload the code onto the Arduino I used Arduino IDE, and followed the GitHub instructions to flash the Ardunio. You simply then install the lightweight program onto your computer and set the applications to each knob.

Finally, you get to reap the benefits of being able to change your volumes on the fly. This project has increased the quality of my life by an insane amount, instead of having to alt-tab from a competitive game, simply turn the knob and crank the volume to hear footsteps or turn down Spotify when joining a discord chat so you can hear your friends.