This one’s concept I saw a long time ago on Instructables.com but it happened to end up being the main project for one of my courses at SFU. I thought that was pretty awesome, do a project I wanted to try and also get marks for it too. During university I had very little time to work on personal projects so it was great to be able to allocate school work hours into something I wanted to do anyways.

The twist is that the course was Microcontroller and Embedded Systems, meaning we were not permitted to use the Arduino used in the step-by-step project tutorial online. We had to learn the architecture of another mcu and use that instead. However the university resources were pretty outdated and they wanted us to use a HCS12 Dragon (educational) board programmed via Freescale Codewarrior. Since I believe I’ll never use this architecture in the future, I wanted to learn something useful instead. I have already been working with Texas Instruments boards for a bit, their Launchpad development boards are stupidly cheap (so much I think they lose money on it). The MSP430 DSPs are equivalent to an arduino and I think are equally capable if not more (imo the biggest difference to me is the community and library support). However in recent years, TI started a new line of products called the Stellaris Launchpads. These are designed as introductory products to their high performance Stellaris products and Stellarisware libraries. I’ve used this before on a Intelligent Display Module Stellaris dev kit (RDK-IDM) for my Capstone.

The Stellaris Launchpad (EK-LM4F120) carries a mcu (LM4F120H5QR ) with absolutely amazing specs for a dev kit that only costs $13. When I bought it they were just introducing it and had a promotion and I got 2 of them for $5 each.

A quick overview of it’s specs:

So I’m using this mcu to control my LED Matrix Cube, it has just enough I/O pins to do it too. My goal is to utilize the DSP parts of it to run a spectrum analyzer on an audio feed and play an animated equalizer on the cube.

After meeting the minimum requirements for the course I have not touched this in a while. During the course I hit a lot of bugs in the firmware that I was not able to resolve and I suspect I will need to rebuild the firmware from scratch in order to continue the project.

The project goal is purely aesthetic and the cube will not really serve any purpose, which is why this is a back burner project. I do hope to eventually get back to this so I can learn more about mcu architecture and embedded programming. I did at least put in the effort to create a CAD model of a nice case and had that made from laser cut acrylic. As you can see in the photo, it has a nice gloss black base (missing some square brackets that are used to keep the lid closed and act as feet). Additionally I had cut a clear acrylic box that goes around the LEDs to protect it.

Story time: About 7 years ago my brother gave me a pair of very awesome Sennheiser ear buds, CX55’s, for my birthday. I had been looking at getting a decent pair for a while and marked out Sennheiser, but wasn’t really sure which model to get. I had my eye on a very expensive pair around ~$120 at the time. Pretty pricey for a pair of ear buds for a high-schooler. So my brother got me a pair, but one of the cheaper models. The actual value of the CX55’s was around $80 at the time. I was a little disappointed at first, but after using them for a bit, I came to love them. The quality was absolutely amazing. I was very sad when the connector wore out 2 years later and I had to start looking for another pair.

After doing a bit of research I was shocked to find the exact same ear buds for sale on Deal Extreme, the cheap Chinese supplied online shopping site. Everything about the Cx55’s were identical, except the price: $12.49 and down to $10.60 if I bought it in bulk… which is exactly what did. I figured if even if they were crap and lasted a couple months, if 5 pairs can last as long as the original for te same price then it was fine.

When they arrived I did a thorough check. The only difference I could find was that the shape of the plastic nub where the L and R wires split was a different shape. The quality of sound, I could hear no difference than the original.

I started using these regularly, but as expected I found that they didn’t last too long, 6 months at best with my regular wear and tear. The common defect among them was the audio jack.

After getting a 3rd gen iPod in 2011 I noted that the audio jack on it was pretty crap. No matter what ear buds I used the connection occasionally disconnected in one channel or both. At the time I thought it was a defective iPod, but after recently getting a similar behavior from a 3rd gen iPhone I believe it’s just a shitty design. I think the apple ear buds have just a slightly longer jack which makes the connection more secure.

After that I decided to try something different. I noted that the iPod docks are often incorporated into speakers which means the proprietary Apple connector feeds audio channels. I bought a cheap connector off of Deal Extrememe, cut the connector and opened it up to find exactly what i was hoping for. So I spliced one of the dead earbuds and tested it out. Perfect audio coming through.

The one and only problem: no volume control. By default the Apple devices will max out the audio signal through the dock connector since it’s expected that the dock device (a speaker) would have it’s own amplifier and volume control. This meant if I wanted to use this I needed a in-line volume controller. I researched a little into this and found I could easily just use a potentiometer per audio line since I have no need of amplification, I only need a negative gain. However, after playing around splicing a few of the other ear buds I know all to well that the wires inside them are extremely delicate and require very good strain relief. This meant I couldn’t just find an existing in-line volume controller and splice it between the cables. I’d never be able to get a decent strain relief that wouldn’t look super ugly.

TL;DR: I bought great quality sounding ear buds with defective connectors and want to splice an Apple connector instead of an audio jack but I need a volume controller with good strain relief.

After purchasing my 3D printer I can now design a plastic module that will hold a pair of potentiometers and provide decent strain relief.