A Simple Laser Harp MIDI Instrument

June 19, 2024 by 5 Comments

Craig Lindley is a technical author and a prolific maker of things. This simple project was his first attempt to create a laser harp MIDI device. While on vacation, Craig saw a laser harp with only three strings and decided to improve upon it by expanding it to twelve strings. The principle of operation is straightforward: twelve cheap diode laser modules aim a beam towards an LDR, which changes resistance if the light level changes when the beam is interrupted.

The controller is a simple piece of perf board, with a Wemos D1 mini ESP32 module flanked by some passives, a barrel socket for power, and the usual DIN connector for connecting the MIDI instrument. Using the ESP32 is a smart choice, removing all the need for configuration and user indication from the physical domain and pushing it onto a rarely-needed webpage. After a false start, attempting to use a triangular frame arrangement, [Craig] settled upon a simple linear arrangement of beams held within a laser-cut wooden box frame. Since these laser modules are quite small, some aluminium rod was machined to make some simple housings to push them into, making them easier to mount in the frame and keeping them nicely aligned with their corresponding LDR.

Sadly, the magnetic attachment method [Craig] used to keep the LDRs in place and aligned with the laser didn’t work as expected, so it was necessary to reach for the hot glue. We’ve all done that!

An interesting addition was using an M5 stack Unit-Synth module for those times when a proper MIDI synthesiser was unavailable. Making this luggable was smart, as people are always fascinated with laser harps. That simple internal synth makes travelling to shows and events a little easier.

Laser harps are nothing new here; we have covered plenty over the years. Like this nice build, which is more a piece of art than an instrument, one which looks just like a real harp and sounds like one, too, due to the use of the Karplus-Strong algorithm to mimic string vibrations.

2024 Business Card Challenge: PCB Business Cards For Everybody

June 19, 2024 by 21 Comments

PCB business cards for electronics engineers might be very much old news in our circles, but they are still cool, not seen too much in the wild, and frankly inaccessible to those in other industries. For their entry into the 2024 Business Card Challenge, [Dima Shlenkevitch] is helping a little to alleviate this by providing a set of design examples and worked costs with suppliers.

Original green is still the cheapest option.

[Dima] lists key features every PCB business card should include, such as the expected thickness, restrictions for placing NFC components, and some aesthetics tips. Make sure to choose a supplier that allows you to remove their order number from the manufactured PCB, or it will look out of place.

Ordering PCBs with these specifications to keep costs reasonable requires effort, so [Dima] offers some example designs along with the results. If you want to have pretty gold lettering and graphics, you will need ENiG plating, increasing the price. Non-standard solder mask colors can also raise the price.

Will this help with the practical aspects of driving the PCB design software and actually placing the order? Obviously not, but the information provided gives you a leg up on some of the decisions so you don’t go down an expensive rabbit hole.

2024 Business Card Challenge

Taking A Look Underneath The Battleship New Jersey

June 19, 2024 by 41 Comments

By the time you read this the Iowa-class battleship USS New Jersey (BB-62) should be making its way along the Delaware River, heading back to its permanent mooring on the Camden waterfront after undergoing a twelve week maintenance and repair period at the nearby Philadelphia Navy Yard.

The 888 foot (270 meter) long ship won’t be running under its own power, but even under tow, it’s not often that you get to see one of the world’s last remaining battleships on the move. The New Jersey’s return home will be a day of celebration, with onlookers lining the banks of the Delaware, news helicopters in the air, and dignitaries and veterans waiting eagerly to greet her as she slides up to the pier.

But when I got the opportunity to tour the New Jersey a couple weeks ago and get a first-hand look at the incredible preservation work being done on this historic ship, it was a very different scene. There was plenty of activity within the cavernous Dry Dock #3 at the Navy Yard, the very same slip where the ship’s construction was completed back in 1942, but little fanfare. Staff from North Atlantic Ship Repair, the company that now operates the facility, were laboring feverishly over the weekend to get the ship ready.

While by no means an exhaustive account of the work that was done on the ship during its time in Dry Dock #3, this article will highlight some of the more interesting projects that were undertaken while it was out of the water. After seeing the thought and effort put into every aspect of the ship’s preservation by curator Ryan Szimanski and his team, there’s no doubt that not only is the USS New Jersey in exceptionally capable hands, but that it will continue to proudly serve as a museum and memorial for decades to come.

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Open Source Your Air Ride Suspension

June 19, 2024 by 8 Comments

Air ride suspensions have several advantages over typical arrangements, but retrofitting a system to a vehicle that didn’t come with it can get pricey fast, especially if you want to go beyond the basics. The Open Source Air Suspension Management Controller aims to give people a fully customizable system without the expense or limitations of commercial units.

The project started as an upgrade to a basic commercial system, so it assumes that you’re bringing your own “bags, tank, compressor, tubing and fittings.” The current board uses an Arduino Nano, but the next revision based on the ESP32 will allow for a wider feature set.

With a Bluetooth connection and Android app, you can control your ride height from a phone or integrated Android head unit. Currently, the app shows the pressure readings from all four corners and has controls for increasing or decreasing the pressure or airing all the way up or down to a given set point.

Want to know how air suspensions work? How about this LEGO model? If you want a suspension with active tuning for your bike, how about this Arduino-powered mod?

Linux Fu: Kernel Modules Have Privileges

June 19, 2024 by 13 Comments

I did something recently I haven’t done in a long time: I recompiled the Linux kernel. There was a time when this was a common occurrence. You might want a feature that the default kernel didn’t support, or you might have an odd piece of hardware. But these days, in almost all the cases where you need something like this, you’ll use loadable kernel modules (LKM) instead. These are modules that the kernel can load and unload at run time, which means you can add that new device or strange file system without having to rebuild or even restart the kernel.

Normally, when you write programs for Linux, they don’t have any special permissions. You typically can’t do direct port I/O, for example, or arbitrarily access memory. The kernel, however, including modules, has no such restriction. That can make debugging modules tricky because you can easily bring the system to its knees. If possible, you might think about developing on a virtual machine until you have what you want. That way, an errant module just brings down your virtual machine. Continue reading “Linux Fu: Kernel Modules Have Privileges” →

A Closer Peek At The Frame AR Glasses

June 19, 2024 by 11 Comments

The Frame AR glasses by Brilliant Labs, which contain a small display, are an entirely different approach to hacker-accessible and affordable AR glasses. [Karl Guttag] has shared his thoughts and analysis of how the Frame glasses work and are constructed, as usual leveraging his long years of industry experience as he analyzes consumer display devices.

It’s often said that in engineering, everything is a tradeoff. This is especially apparent in products like near-eye displays, and [Karl] discusses the Frame glasses’ tradeoffs while comparing and contrasting them with the choices other designs have made. He delves into the optical architecture, explaining its impact on the user experience and the different challenges of different optical designs.

The Frame glasses are Brilliant Labs’ second product with their first being the Monocle, an unusual and inventive sort of self-contained clip-on unit. Monocle’s hacker-accessible design and documentation really impressed us, and there’s a pretty clear lineage from Monocle to Frame as products. Frame are essentially a pair of glasses that incorporate a Monocle into one of the lenses, aiming to be able to act as a set of AI-empowered prescription glasses that include a small display.

We recommend reading the entire article for a full roundup, but the short version is that it looks like many of Frame’s design choices prioritize a functional device with low cost, low weight, using non-specialized and economical hardware and parts. This brings some disadvantages, such as a visible “eye glow” from the front due to display architecture, a visible seam between optical elements, and limited display brightness due to the optical setup. That being said, they aim to be hacker-accessible and open source, and are reasonably priced at 349 USD. If Monocle intrigued you, Frame seems to have many of the same bones.

Bent Shaft Isn’t A Bad Thing For This Pericyclic Gearbox

June 19, 2024 by 14 Comments

With few exceptions, power transmission is a field where wobbling is a bad thing. We generally want everything running straight and true, with gears and wheels perfectly perpendicular to their shafts, with everything moving smoothly and evenly. That’s not always the case, though, as this pericyclic gearbox demonstrates.

Although most of the components in [Retsetman] model gearboxes seem familiar enough — it’s mostly just a collection of bevel gears, like you’d see inside a differential — it’s their arrangement that makes everything work. More specifically, it’s the shaft upon which the bevel gears ride, which has a section that is tilted relative to the axis of the shaft. It’s just a couple of degrees, but that small bit of inclination, called nutation, makes the ring gear riding on it wobble as the shaft rotates, allowing it to mesh with one or more ring gears that are perpendicular to the shaft. This engages a few teeth at a time, transferring torque from one gear to another. It’s easier to visualize than it is to explain, so check out the video below.

Gearboxes like these have a lot of interesting properties, with the main one being gear ratio. [Retsetman] achieved a 400:1 ratio with just 3D printed parts, which of course impose their own limitations. But he was still able to apply some pretty serious torque. The arrangement is not without its drawbacks, of course, with the wobbling bits naturally causing unwelcome vibrations. That can be mitigated to some degree using multiple rotatins elements that offset each other, but that only seems to reduce vibration, not eliminate it.

[Retsetman] is no stranger to interesting gearboxes, of course, with his toothless magnetic gearboxes coming to mind. And this isn’t the only time we’ve seen gearboxes go all wobbly, either.

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