midiMixer - A simple Arduino powered MIDI potentiometer bank

William Floyd — Wed, 06 May 2020 00:00:00 +0000

This is nothing too special really - I wanted to try my hand at designing a custom PCB and assembling a device from scratch. GitHub for this project.

This story actually starts a while ago (perhaps 2015), when I got the desire to build a DJ control panel (with no knowledge of how to get into it). This never really happened, but it did lead me to get to know some DAW software, and experiment with it off and on. But in the back of my head I still wanted to build some hardware to help with this.

This eventually came about in the summer of 2019, when I finally hand-wired a simple 8 knob control surface. Truth be told, I actually built two. The first one had some issues (I wonder why…?), and would sporadically jitter values. The second one worked correctly, having been wired much more carefully.

Still, it was lacking professionalism, polish, and most importantly, robustness. The sandwich of 22AWG wire, cardstock and PCB was less than sturdy, so I promptly packed it away and never used it. Around this time also, I tried very briefly to learn how to use KiCAD, but didn’t get far at all. This would come to change, however, in April of 2020.

Fast forward close to a year, and here we are - toilet paper is the currency of the quickly collapsing Covid19 crazed world, and I’m back with my grandparents for the remainder of my semester (which, as of writing, is all but concluded). Finding my lack of a social life leaving me with a little bit more free time, and being home yielding a lot more distractions, I learned the basics of KiCAD from YouTube, and set out to design a simple PCB. My old MIDI controller project came to mind, so I set myself to it, and within a few days had my first Gerber files sent off to JLCPCB. In reality, I should have waited a bit and done a couple more design iterations before committing, but I guess $7 is the price of impatience.

So it was that my crisp PCBs showed up 3 weeks later - I had one assembled within the hour, and my old code dusted off and flashed within two hours. It’s really as simple as it gets - a Pro Micro hooked up to a 4051 analogue multiplexer, in turn hooked up to 8 potentiometers.

The potentiometers I had on hand ended up being a bit different than the footprints I had used, so I ended up having to clip the mounting tabs off of them. This, as one might imagine, made them extraordinarily flimsy, so I designed and printed a couple clamps to align and hold solid the potentiometers. These also have the added benefit of keeping the soldered pins off of whatever surface the mixer is on. Should the correct potentiometers be used, these would not be needed, though some feet or a case for the PCB would still be best.

This being my first PCB design, I am quite happy it worked out so well - I am studying for Mechanical Engineering, not Electrical… However, I see room for improvement. The potentiometers are too close together, and the rows are too far apart. The knobs barely clear the Arduino, and the Arduino is mounted far higher off the PCB than I would like. I see myself making a v2 in due course - perhaps next time I will try JLCPCB’s SMT assembly? I imagine adding indicator LEDs, improving the layout, and adding a button to switch between banks would make this much more useful.

Clickbait - The Automatic Fishing Caster

William Floyd — Fri, 13 Mar 2020 00:00:00 +0000

This project was completed in the Fall Semester of 2019, for my EPM class at LeTourneau University.

The mandate given to us was as follows:

Create a device to launch a fishing weight. It must:

be capable of selectively launching 20 and 40 feet
weigh less than 5 pounds
cost less than $100
be battery powered
be capable of firing 30 times over the course of 1 hour
(for extra credit) be wirelessly controlled

And so it was that we began brainstorming.

The idea was fairly simple - use two smooth rods and a leadscrew to pull a carriage against springs that would then somehow fire the fishing weight. The choice of this mechanism was, for the most part, due to availability of parts. I already owned the necessary rods and bearings, and springs were readily available.

Soon, we had some basic 3D printed parts in order - for it was 3D printing that was most accessible to us, and allowed largely unattended manufacturing while classes continued. Despite this early start of progress, however, the ever present tendency toward procrastination crept in. The usual array of excuses were made by all, and little actual work was accomplished.

So it was that we inched ever closer to the deadline. Past the basic idea of our launch mechanism, all else was yet to be decided. A few calculations were half-heartedly done (kinetic energy, spring constants, etc.), but we all knew we didn’t know enough to make any meaningful decisions yet. We had some very much unfounded fears concerning battery power, and not enough fears concerning torque - we believed we would be using NEMA 17 motors to tension the leadscrew. Needless to say, this did not turn out to be realistic. Nor was it realistic for us to budget a baitcasting reel instead of a much cheaper spincaster.

Eventually, however, some progress was made - progress in something of a wrong direction, but progress nonetheless. As the shape of our ungainly creation began to emerge, it was clear progress needed to be made quickly. Once we coupled our stepper motor to the leadscrew and power tested the unit, it was also clear that change was in order.

So a decision was made: a cheap cordless drill would be pilfered for a battery, motor and chuck. An H-Bridge would need to be bought for the drill motor (I tried to make one, but the magic smoke was released…), and a latching system needed to be made.

The next week or so resulted in the beginnings of a working launch mechanism. With the aid of a rubber band, a latching track was put under the rods and springs, such that the motor would tension the launching carriage, then return to the front of the mechanism to allow the eventual release of the catch using a servo. Soon after this, the motor was appropriately mounted to the frame, with a carefully fit 3D printed socket. It was, it seemed, all coming together.

▶ Watch the video

Finally, some success came to us. The motor was successfully power tested, along with the release of the launch mechanism. The end was near, or so it seemed.

Following soon after was the reel being mounted to the device also. Attempts were made to use a small DC motor, but with no luck. The lateral pressure of our motor acting through a belt meant friction was too much for our motor. Without time enough to reposition it, another solution had to be made.

Remaining at this point was a means of reeling in the line, a means of depressing the button on the rear of the reel, a limit switch at the front of machine, and the connecting electronics that would drive the entire contraption.

As it turned out, the very same stepper motor that had once tried to turn our leadscrew now instead would be pressed into service reeling in the line. Overkill, to be sure, and its power most wastefully used, it did indeed reliably turn our reel, albeit slowly. The use of such a large pulley was a matter of making it fit the belt size that I had available. The next size down was too small, so the pulley had to be enlarged. This saved the most time 3D printing as compared to a smaller pulley with other parts changed.

Finally, the mechanics of the project were completed, with each component individually power tested, though not yet in tandem with one another. As all of this was coming about, I had also begun getting the electronics in order. A limit switch was installed to keep the motor from destroying the machine. When this switch invariably failed to activate, it resulted in the destruction of the front piece of the machine - at that stage more of a nuisance than a disaster. Spares were kept by, and small changes were made so the switch could be mounted elsewhere in a more reliable fashion.

By way of a multi-button garage door opener, and a 433MHz receiver, wireless control could be granted to an Arduino for little money. A cheap buck-converter was added in order to run the Arduino and wireless setup, as well as the stepper motor driver. Thankfully, the voltage of the battery meant the stepper motor could be powered from the battery directly (18V being safely within the rated 12-24V range)

▶ Watch the video

In the above video, the finished product may be seen.

Finally, presentation day came. Not without some small failings, we presented, with acceptable results. The largest remaining issue was the fact that the leadscrew would slip the grasp of the chuck after several cycles of the machine. While we corrected by hand for the presentation (by re-chucking the leadscrew after each launch), we knew we needed to fix the slippage for good. After all, the final time-lapse of the project would not do with such continual, and blatant, hand-holding.

The solution, it turned out, was free: the end of the leadscrew was notched and tapered on a lathe, allowing the drill chuck to get a firm hold on the metal.

▶ Watch the video

With this solved, the final time-lapse was completed, and a collective sigh of relief was given.

Much was learned - how to more properly budget for a project, how to work with a team (something I need to improve on), and how to manage time well. All things considered, I found it to be a success - I did not pull an all-nighter for my own project, finishing with a few days to spare (no small thanks to an extended deadline), nor did I stress myself beyond all reason. Overall then, I enjoyed the experience of finally bringing a project to completion - this is something I do not often do, try as I might. The result, though useless for my own purposes, is something I am proud of, having taught me many things through its completion.

SolidWorks on William Floyd (high-quality images)

midiMixer - A simple Arduino powered MIDI potentiometer bank

Clickbait - The Automatic Fishing Caster