V2 of the Motorized Fader Per-App Volume Controller!

Hello there and welcome to my Instructable. In this Instructable, I'll be walking you through how to build V2 of my DIY Per-App volume mixer system with motorized faders - and let me tell you, if you thought V1 of this project was cool, you'll love V2. I think this thing came out so great, so come on, let's build it!

This project is pretty heavy on the supplies, so buckle up! Unless it's specifically noted, all links are non-affiliate links.

Electronic Parts:

1x Teensy 4.1 Microcontroller

3x DRV8833 Motor Driver Module

1x MT3608 Boost Converter

1x L7805CV 5V Voltage Regulator

5x 2N3904 NPN BJT

5x 330 Ohm Resistor

13x 1 Kilohm Resistor

15x 0.1uF (100nF) Ceramic Capacitor

1x 10uF Ceramic Capacitor

3x 47uF 16V or 25V Electrolytic Capacitor

1x 100uF 16V or 25V Electrolytic Capacitor

1x 2-Pole Screw Terminal

5x 100mm Behringer X32 Replacement Motor Fader

5x 16mm Red Illuminated 12V LED Latching Pushbutton

8x 12mm Momentary Pushbutton

5x 0.96" 128x64 I2C OLED Display

1x B100K Potentiometer with Knob

1x 5.5x2.5mm Barrel Jack

1x Micro-USB Male to USB-C Female Cable

1x 9V 2A Power Adapter

DuPont Cables

Hookup Wire

Mechanical Parts (Fasteners):

12x M3x12 Countersunk Screw

14x M3x8 Countersunk Screw

2x M3x6 Countersunk Screw

2x M3x10 Socket Head Screw

1x M3x4 (or x6) Socket Head Screw

10x M2x4 Socket Head Screw

17x M3 Hex Nut

4x M3x15+6 Standoff

Here are some kits that will give you all the fasteners needed for this project plus a bunch more for future ones!

M3 Countersunk Screw Kit

M3 Socket Head Screw Kit

M2 Socket Head Screw Kit

M3 Standoff Kit

Custom Manufactured Parts:

Custom PCB - This project requires a custom PCB for the main electronics. You can choose to download the Gerbers and order them from wherever, or you can order the PCB directly with the button on the page from this link. If you do this, I will get a small kickback from your purchase that helps the channel.

Custom CNC'd Faceplates - There are two .STEP files attached on this section of the Instructable, one for the main fader plate and another for the scribble strip plate. These parts are designed to be custom CNC machined, and they give the project an incredibly premium overall feel if made out of Aluminum. If you want these parts custom machinesd like I did, I recommend going to Justway (the YouTube sponsor for this project), and using their custom CNC service to make both pieces. I also recommend getting the parts finished with a bead-blast and anodized finish, I went with anodized clear, but you can choose any color you want. Finally, if the custom CNC'd parts are too expensive for you to justify in comparison to a cheaper 3D print, which is fair, there are STL versions of the 3D files available as well that you can use to 3D print these plates and the final build should work just fine with 3D printed plates.

3D Printed Parts - There are a few 3D printed parts that go with this project, assuming you're having the faceplates CNC'd. The Main Chassis.stl, Scribble Strip Holder.stl, and USB Port Mount.stl files can all be 3D printed using a standard FDM printer in a filament like PLA or PETG. If you don't have a 3D printer, check out Justway's (the YouTube sponsor of this project) 3D printing service to get these parts made. Once those parts have been printed using a more common 3D printing method/material, you'll also need to print/have printed 5 of the Fader Knob.stl files, and I HIGHLY recommend getting these resin printed either by yourself if you have the printer or by Justway (I used Justway's service for mine and used the PWR Dark Black material).

ATTRIBUTION: The Fader Knob 3D model was sourced from dylanmccarter2003 on Thingiverse at this link.

I made a YouTube video on this project, so before jumping into building it, go ahead and watch that! It will give you a great idea of how this V2 has improved over V1, what building V2 will entail, and of course, what V2 actually does once it's completed.

The first step to building this project is to assemble the PCB. Overall, this board is really easy to assemble, though there are a few important notes to pay attention to when building it. Firstly, while I didn't list female headers in the materials list, if you have them, I would strongly recommend using them to place the motor driver modules and the Teensy in sockets so they can be unplugged and swapped out. Also, this is the point where you should use the one M3x4 (or x6) screw and nut to hold the L7805 down to the PCB.

One of the other things to pay attention to at this stage is all of the places on the board to solder headers for the peripheral components, those being things like the buttons, faders, and screens. What's important with these spots is that you don't solder headers to any of them! (I soldered headers to a few of them but ignore this, as I later removed the headers due to this being a mistake) Leave them as empty pads, and later, we'll be making all of the connections straight to the PCB by soldering hookup wire from point to point. Also, there's a 2-pin header footprint labeled "+12V EN", don't solder anything to that spot yet either.

Finally, there's something to pay attention to on both the Teensy and the motor driver modules before they're soldered to the board: On the underside of the Teensy, there are two relatively large rectangular pads near the USB port, and these pads are very close together. Right in-between the pads, there's a small trace that connects the pads together, and we need to cut this trace so that power to the Teensy is provided by the 5V rail created from the power adapter, and not through the 5V from the USB connection. After you sever this trace with a razor blade, you can verify that it's cut by either using continuity mode on a multimeter and making sure there's no connection between the two large pads, or you can plug the Teensy into a computer with USB, and the Teensy should not power up when plugged into USB if the trace is severed correctly.

As for the motor drivers, ensure that the small jumper on the back of the board labeled J2 gets shorted with a blob of solder on each of the three motor drivers. If this jumper is left open, the driver boards will default to a sleep mode, and won't be able to actually move any of the motors. When this jumper is shorted, it kicks the drivers out of sleep mode, so that they can move the motors properly for this build.

Schematic attached to this step if it helps you while assembling the board :)

There's a boost converter on this PCB that needs to be tuned to output 12V with the 9V input from the adapter. Before the output of this boost converter can be connected through to the rest of the circuit by shorting the "+12V EN" contacts with some solder, we need to ensure it's actually outputting 12V and not 26V or something. There are two test points provided on the board to use a multimeter to measure the module's output voltage when the board is being powered through the PWR IN jack with 9V. So, measure these test points and if the output isn't 12V, adjust the potentiometer on the module until it is. Once you've got 12V on the output, go ahead and power down the board and then use some solder to short the two contacts on the "+12V EN" header.

Next up, we're going to start mounting everything to the large CNC'd fader plate, as this part basically becomes the heart of the whole build.

Starting with the 5 motor faders, each fader can be mounted to the plate by using 2 M3x12 countersunk screws and matching M3 nuts. Make sure these screws and nuts are nice and tight, but be careful not to absolutely crank them down, or they'll deform the frame of the motor fader and the fader will stop moving smoothly.

As for the orientation of the faders, ensure that the motors on the faders are oriented to be closer to the holes for the mute buttons.

Now, using the included hardware (minus the O-ring), you can mount all 5 of the 16mm latching pushbuttons to the fader plate. These buttons will act as the mute buttons, and I recommend mounting them so that all of their terminals face the same way for consistent wiring later. I had my buttons oriented so that the NC contact of the switch was closest to the fader motors, and the two LED connections were facing left and right when the faders were vertical. Also, make sure you crank these nuts down! It would suck if one of the buttons came loose once the whole device is closed up.

Next we can mount the 8 12mm momentary pushbuttons that allow you to switch between and store mix presets. These buttons are mounted exactly like the bigger ones, that is, using the included mounting hardware (minus the O-ring), and make sure they're TIGHT. I also recommend orienting the buttons so that if you were to draw a line connecting the two terminals on them, the line would be perpendicular to the faders.

Next up, using four M3x8 countersunk screws, four M3x15+6 standoffs, and four M3 nuts, we can mount the PCB to the fader plate. Find the four holes in a rectangular pattern that line up with the holes in the PCB (the PCB should mount over the backs of the five faders), and use the countersunk screws to screw the standoffs into the front plate, so that the little nub of threads on the standoff is sticking out on the back side of the panel. Once all four standoffs are tightened to the front panel well, bend down the small tabs on the backs of the faders so that they won't short out against the PCB. Then, set the PCB on the four screw pegs now on the back, so that the motor drivers are closer to the fader motors and the Teensy is further from the motors, and lock everything down with the four M3 nuts.

Now we get to wire up all of the connections between the peripheral components and the PCB! While this is technically a single subject of operation, instead of trying to bunch everything into one big, overwhelming step, I've split it between the next few steps, so let's get started because there's a lot of wires to hook up.

Starting right between the motors on the faders and the PCB, there are several connections to make in this area, but we'll start with the two simplest: The ground for the fader potentiometers, and the fader motor connections.

For the fader grounds, know that the faders (and the mute buttons/motors, for that matter), are named Fader/Motor/Mute 1-5, with number 1 being the leftmost fader when the final product is assembled. So, if your faders are rotated upside down currently, take that into account. Thankfully, all of the connection points should align with the faders, so the connections for Motor 1 should be right there, in line with Motor 1. In any case, use some basic hookup wire to connect between the pin labeled "3" on faders 1-5 and the matching ground point for each fader. So, pin 3 of Fader 1 connects to "Fader 1 -" on the PCB. Don't worry about pin 4 on the faders, that's left unconnected for this project.

Alright, now that you've got all 5 fader grounds done, let's do the motors. Cut off the connectors on the fader motor wires right at the base of the connector, so that you don't have to extend the wires already coming off of the motors. Then, connect Motor 1 to Motor 1 on the PCB, and connect the wire coming off the motor that has a big red stripe on it to the positive terminal of the Motor 1 PCB connection, and the wire that doesn't have this stripe goes to the negative terminal.

Ensure the ground and motor connections for all 5 faders are complete and then move on to the next step.

Now on the opposite edge of the PCB, we can connect pins 1 and 2 of each fader to the fader's positive (+) connection, and the wiper connection. As with the previous connections, all of the connections should really just go in a straight line from fader to PCB terminal, so as long as you don't have wires crossing, you're probably doing it correctly.

Pin 1 of each fader connects to that corresponding fader's positive (marked with a +) terminal, and Pin 2 of each fader gets connected to the corresponding fader's "Wiper" terminal.

Now we get to wire up the 8 12mm pushbuttons that are used to store and recall the saved mixes. These are a little bit less cut and dry than the connections we've just done, so pay some extra attention here.

The really important part is that one terminal of every single button gets connected together to one big common terminal, and this common terminal connects to the "+3.3V" terminal on the "Mix Buttons" header on the PCB, which should be right next to the buttons.

Once you've made this common terminal connection using hookup wire, the other terminal of each button goes to the B1-B8 terminals on the "Mix Buttons" header. Like before, everything stays in order, so the button that is furthest left connects to the "B" terminal that's also furthest left. As long as none of your wires have to cross over or under each other to reach their destination (excluding the +3.3V common), you should be doing it right.

Another way to put it is B1 is the button closest to the mute buttons, and B8 is the one furthest, and they all stay in order throughout their path away from the end of the panel with the mute buttons.

Alright, get ready because this is one of the hardest wiring parts of this project.

There is a total of four wire connections to make to each mute button. Two for the button's switch contacts, and two for the LED inside the button that allows it to illuminate red when pressed.

Let's start with the switch contacts. There should be labels on the back of the switch that indicate the "COM" (sometimes just labeled "C"), "NC", and "NO" contacts. On the PCB, each mute button gets the connections LED+, LED-, BTN1, and BTN2. The wiring for the switch contacts is to ensure that BTN1 and BTN2 for each switch get connected to the "COM" or "C" contact, and the "NO" contact for each button. It doesn't matter if BTN1 is connected to COM and BTN2 is connected to NO, or if BTN1 is connected to NO and BTN2 is connected to COM, as long as both connections are made (regardless of order), this part of the circuit will work fine.

The part that is not as agnostic to connection order has to do with the LED for each button, as if these are done backwards, they won't illuminate. I recommend using a bench power supply set to 12V output to find the LED contacts for your buttons and find out which contact is + and which is -. Then, for each mute switch, the + connection of the LED goes to LED+ on the PCB, and the - connection of the LED goes to LED - on the PCB.

Once you get all four wires ran for each of the 5 buttons, you're good to move on to the next step!

Before we can mount the OLEDs to their panel and wire these parts up to the PCB, we need to solder cables on to these parts. I used DuPont cables for this, as I was easily able to use some male-female DuPont cables to extend the reach of a few of the OLED's cables as well as the knob, but honestly, if you want to cut lengths of hookup wire for these connections, go for it. As long as we get four cables from each OLED and three cables coming from the potentiometer, and the cables are long enough to reach the motherboard when the OLEDs and knob are in position (preferably with some slack for ease of assembly), everything should work fine.

In any case, as I said, we need four wires from each OLED: SDA, SCL, VCC, and GND. Then, we need three wires from the potentiometer. And remember, for the potentiometer and three of the five OLEDs in my case, I had to extend the wires shown in these photos, so don't take the lengths in the photos as gospel.

Now before we move on, there's one more thing to do with the OLED displays! We need to change the address on two of the 5 displays from the default of 0x3C to 0x3D by moving the small resistor on the back, resulting in three screens with an address of 0x3C and two screens with an address of 0x3D. Here's why:

We need to be able to address each of the 5 OLED displays separately, and these displays offer two different addresses to do this with. Of course, this means that on one I2C bus (without a multiplexer), we can only have two displays independently controlled. Thankfully, the Teensy 4.1 has three I2C buses, so we can put two uniquely addressed displays on I2C bus 0, another two on I2C bus 1 (doesn't matter if they're the same addresses as the screens on bus 0, they're on different buses and won't interfere), and then we can place one more display on I2C bus 2. That's why we only have to change the addresses on two of the screens, but keep track of which displays have which address, because the physical order of these screens when we mount them matters.

Now we'll take the five OLED displays and the 3D printed "Scribble Strip Holder", and we'll use 10 M2x4 screws to mount the screens to this 3D printed piece. Only use the bottom two screw holes of each OLED to mount them, and when mounting them to this piece the order they're in (addresses) matters.

What you want is, from left to right, screens with addresses in this order: 0x3C (default), 0x3D (changed), 0x3C, 0x3D, 0x3C. This will ensure that the scribble strip display for fader 4 is displayed above fader 4 and not fader 3, that wouldn't be what we want!

Now, using the included nut and washer, go ahead and mount the potentiometer to the CNC'd scribble strip plate. Pay attention to the potentiometer's orientation, as there's a very small hole in the CNC'd plate for the anti-rotation nub on the potentiometer to slot into that you'll want to make sure gets aligned and locked into place properly.

Here's where the single worst part of the assembly gets born, because we're about to tether the potentiometer assembly and the OLED assembly to the motherboard with soldered wire connections. Thankfully we won't be dealing with this octopus for long, but for now, it's time to build it.

Thankfully, the wiring is pretty simple. Connect the potentiometer's three wires to the AUXPOT terminal on the PCB, so that the leftmost pin of the potentiometer is connected to the - connection, the middle pin is connected to the wiper connection, and the rightmost potentiometer pin is connected to +.

Then, for the OLED displays, the leftmost OLED when facing the front of the screens will be connected to the OLED 1 header on the PCB. Be super careful to make sure that VCC, GND, SCL, and SDA get connected in the correct order from the screen all the way down to the PCB. The pinout of the connection points is labeled on one of the headers for the OLEDs on the PCB, and the order is the same for all 5 headers. Then, continuing from left to right, OLED 2, OLED 3, OLED 4, and OLED 5 is the rightmost OLED when you're facing the front of all of the screens.

Now, set all of that aside, and bring out your Main Chassis 3D print and the barrel jack, as well as two ~1-foot lengths of hookup wire. Use the included nut and washer to mount the barrel jack into the hole for it in the back of the chassis and solder the hookup wires to the center and outer pin of the jack, preferably with some color code that indicates which cable is positive (center pin) and which is negative (outer pin).

The standard 22AWG hookup wire should be fine for these connections, but if you want to beef it up to some thicker wires if you have them on hand, that would be a great idea. I used 18AWG cables from an old PC power supply for these connections in my build.

After the barrel jack is done, grab your 3D printed USB port mount and the micro-USB male to USB-C female cable you ordered from the materials section. Feed the micro-USB end through the 3D print so that you can eventually fit the female USB-C end into the mount like shown in the photos after passing the whole cable through. Once the cable's fitted into the print, secure the USB-C end to the print with some hot glue to ensure it won't budge when plugging a USB-C cable in and out of it.

Now, with the addition of two M3x10 socket head screws and matching nuts, you can mount the USB-C port to the chassis like shown in the photo.

We made it! We're ready to drop everything into the chassis! Now, before we can technically drop everything in, we have to connect the cables from the barrel jack to the power input screw terminal on the PCB, positive to positive and negative to negative, and then we have to plug the micro-USB cable into the USB port on the Teensy. But once that's done, we can flip the main plate over and drop it and all of its electronics straight into the main chassis.

Then, we can take the OLED assembly and the CNC'd plate with the potentiometer mounted to it, and using two M3x6 screws in the two middlemost screw holes in the CNC'd plate (they're really not in the middle, but they're between the two sets of screws on the ends), and after aligning the OLED screens to the CNC'd plate, you can lightly tighten the M3x6 screws to half secure the OLED plate to the CNC'd cover. Do NOT tighten these two screws fully, in fact, don't tighten them at all, just install them enough to hold things in place but not tightly. If you tighten them at this stage, you'll provide a lot of uneven pressure to the OLED displays and will likely break at least one of them and replacing that would be a pain.

Once things are roughly in shape, we can align the OLED assembly with the CNC'd plate onto the main chassis and, using two M3x12 countersunk screws on the left and two M3x8 countersunk screws on the right, mount it in place to the main chassis. At this point, using the two leftmost screws and that middle set, you can set the amount of pressure the OLED displays are mounted with, just be careful not to damage them. The two screws on the right can be tightened normally by the way, as they don't apply mounting pressure to the OLEDs.

After the scribble strips are mounted, use 8 M3x8 countersunk screws to mount the main fader plate to the main chassis.

Press on the potentiometer's knob, and for the faders, I placed small pieces of masking tape on their posts to ensure that the resin 3D printed fader knobs would fit nice and tight on there.

We're really on the final step of the project with regards to the hardware, this is exciting! Plug the 9V power adapter into the barrel jack and plug a USB-C cable into the USB-C port on the back and plug it into your Windows computer.

Then, open the provided Arduino code in Arduino IDE, ensure you have Teensyduino and the necessary additional libraries installed (Here's how to install Teensyduino, and the only library you'll need that you may not have defaulted is Adafruit_SSD1306, here's how to install that), select the Teensy 4.1 as the board, select the port, in the same menu as where you selected port, find "USB Type" and select "MIDI", and upload the code AFTER entering your scribble strip names!

Look for the section of the code that's commented with instructions to replace the text in the quotes with your custom labels. Label 1 goes to the leftmost fader; Label 5 goes to the rightmost fader. If you want to find this section quickly, just CTRL + F "String", and it should take you right there.

Alright, and now that the build process is complete, let's run over how to set up and use the software this thing interfaces with on the PC - MIDI Mixer.

First off, download MIDI Mixer from their website and go through the installer.

The first step is to create a new profile, using the "+" button near the top left of the software (highlighted in red)

At the top of the software, choose the input you want to listen to (Should show up as Teensy MIDI), and this is highlighted in the first image.

In the sidebar (that's kind of in the middle and is highlighted in red in the second image), click on the "Co." button to enter the controls submenu. Here, we'll map all of our faders, buttons, and the knob to MIDI Mixer.

(Reference third image for highlighted buttons for this section) To map a control, click the "+" button to add a new control, name it something sensible (i.e. Fader 1, Knob, Mute 1, etc), ensure the correct type is set (for the faders and the knob, choose fader as the type, and for the mute buttons, choose button). Then, click "Learn Entire Control", and move the fader/press the button/twist the knob that you're adding on the mixer itself. You should see the software recognize that and the numbers in Channel, Control, and the Command should change to reflect the unique control you moved.

Add all 5 faders, all 5 mutes, and the knob like this. The preset buttons on the right-hand side of the mixer do not communicate with the computer via MIDI and don't need to be added.

On the sidebar where we selected the "Co." menu before, move up to the "Gr." menu, and click the highlighted "+" button to create a new Group. Think of these groups as control groups, these groups will be assigned the physical controls on our mixer at our discretion, and different apps/input/output devices will be added to the different groups to be controlled.

Name the new group whatever you want and then assign the Volume control of the group to the physical control you want to control said group. So, say I was making a Music group, and I wanted that to be controlled by Fader 3, I'd select the control I just added for Fader 3 as the volume control for the Music group, and I'd also select the control for Mute 3 as the mute control for the Music Group.

This mixer can support up to 6 total groups - 5 groups with mutes, one for each fader/mute button combo, and one more group that gets assigned the Knob as the volume control and nothing for the mute control.

Here comes the final step: Assigning your apps/devices to the groups! Use the sidebar to move up to the menu right above the "Gr." menu, and here's where we assign the items to the control groups we've just built.

So, say you have a Music group controlled by Fader/Mute 3, you'll want to open Spotify/Apple Music/Whatever and assign it to that group. You can assign multiple things to one group, and whatever level that group is at is the level that all items within the group will be at as well.

As you can see in my example, I have multiple games in the "Games" group. Additionally, I have a main system output on the "Main" group I made (controlled in my case by the knob), and this gives me physical control of my main system output level. Additionally, on the "Mic" group, I have an audio input that I can control the level of going into my computer, and I can also mute it - so I've got a physical mute for my mic, pretty cool!

I hope you enjoyed building this project, and I hope it works well for you! If you made it, please share an "I Made It" below, because I'd love to see it!

Also, if the demonstration in the YouTube video didn't cover it well enough for you, here's how the board itself works and how to operate it:

Each fader controls a group in MIDI mixer, and each group can have different apps/devices assigned to it.

When a group is muted using the mute button, it doesn't matter what level the fader is at, no sound will come out of whatever is in that group

When a group is not muted using the mute button, the fader controls the level of whatever is assigned to its group

If you have a set mix that you want to save, choose which of the 8 slots (represented by the 8 buttons on the right side) you want to save the mix to. Hold the button you want to save the mix to for 2 seconds, and then let it go. You should get a message indicating the preset was saved to that slot, and now when you short press that button, the faders will zip right to the positions you saved in that slot. Do note that the level of the knob is not saved in these presets, nor are the positions/statuses of the mute buttons. These presets only store and recall the positions of the 5 faders.