Impedance Mismatch

March 19, 2022 by Elliot Williams 66 Comments

There are a few classic physics problems that it can really help to have a mental map of. One is, of course, wave propagation. From big-wave surfing, through loudspeaker positioning, to quantum mechanics, having an intuition for the basic dynamics of constructive and destructive interference is key. Total energy of a system, and how it splits and trades between kinetic and potential, is another.

We were talking about using a bike generator to recharge batteries on the Podcast last night, and we stumbled on a classic impedance mismatch situation. A pedaling person can put out 100 W, and a cell phone battery wants around 5 W to charge. You could pedal extremely lightly for nearly three hours, but I’d bet you’d rather hammer the bike for 10 minutes and get on with your life. The phone wants to be charged lightly — it’s high impedance — and you want to put out all your power at once — you’re a low impedance source.

The same phenomenon explains why you have to downshift your internal combustion automobile as you slow down. In high gear, it presents too high an impedance, and the motor can only turn so slowly before stalling. This is also why all vibrating string acoustic instruments have bridges that press down on big flat flexible surfaces, and why horns are horn shaped. Air is easy to vibrate, but to be audible you want to move a lot of it, so you spread out the power. Lifting a heavy rock with human muscle power is another classic impedance mismatch.

If these are fundamentally all the same problem, then they should all have similar solutions. The gear on the bike or the car, the bridge on a cello, the flared horn on the trumpet, and the lever under the boulder all serve to convert a large force over a short distance or time or area into a lower force over more distance, time, or area.

Pop quiz! What are the common impedance converters in the world of volts and amps? The two that come to my mind are the genafsbezre and the obbfg/ohpx pbairegre (rot13!). What am I missing?

Learn To Play Guitar, Digitally

March 2, 2022 by Bryan Cockfield 13 Comments

Learning to play a musical instrument takes a major time commitment. If you happened to be stuck inside your home at any point in the last two years, though, you may have had the opportunity that [Dmitriy] had to pick up a guitar and learn to play. Rather than stick with a traditional guitar, though, [Dmitriy] opted to build his own digital guitar which is packed with all kinds of features you won’t find in any Fender or Gibson.

The physical body of this unique instrument is entirely designed by [Dmitriy] out of 3D printed parts, and uses capacitive touch sensors for each of the notes on what would have been the guitar’s fretboard. The strings are also replaced with a set of six switches that can be strummed like a regular guitar, and are used to register when to play a note. After a few prototypes, everything was wired onto a custom PCB. The software side of this project is impressive as well; it involved creating custom firmware to register all of the button presses and transmit the information to a MIDI controller so that the guitar can communicate digitally with anything that supports MIDI.

To finish off the project, [Dmitriy] also added a wireless device as well as some other bonus features like an accelerometer, which can be used to augment the sound of the guitar in any way he can think of to program them. It’s one of the most innovative guitars we’ve seen since the prototype Noli smart guitar was unveiled last year, and this one is also on its way from prototype to market right now.

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Custom Piano Tickles The Ivories

January 28, 2022 by Bryan Cockfield 6 Comments

The core ethos of “hacking” is usually interpreted as modifying something for a use that it wasn’t originally built for. Plenty of builds are modifications or improvements on existing technology, but sometimes that just isn’t enough. Sometimes we have to go all the way down and build something completely from scratch, and [Balthasar]’s recent piano-like musical instrument fits squarely into this category.

This electronic keyboard is completely designed and built from scratch, including the structure of the instrument and the keys themselves. [Balthasar] made each one by hand out of wood and then built an action mechanism for them to register presses. While they don’t detect velocity or pressure, the instrument is capable of defining the waveform and envelope for any note, is able to play multiple notes per key, and is able to change individual octaves. This is thanks to a custom 6×12 matrix connected to a STM32 microcontroller. Part of the reason [Balthasar] chose this microcontroller is that it can do some of the calculations needed to produce music in a single clock cycle, which is an impressive and under-reported feature for the platform.

With everything built and wired together, the keyboard is shockingly versatile. With the custom matrix it is easy to switch individual octaves on the piano to any range programmable, making the 61-key piano capable of sounding like a full 88-key piano. Any sound can be programmed in as well, further increasing its versatility, which is all the more impressive for being built from the ground up. While this build focuses more on the electronics of a keyboard, we have seen other builds which replicate the physical action of a traditional acoustic piano as well.

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A wooden xylophone with electronic contraptions for robotic playback

Robotic Xylophone Makes Music With MIDI Magic

January 27, 2022 by Chris Wilkinson 8 Comments

The MIDI format has long been used to create some banging electronic music, so it’s refreshing to see how [John P. Miller] applied the standard in his decidedly analog self-playing robotic xylophone.

Framed inside a fetching Red Oak enclosure, the 25-key instrument uses individual solenoids for each key, meaning that it has no problem striking multiple bars simultaneously. This extra fidelity really helps in reproducing the familiar melodies via the MIDI format. The tracks themselves can be loaded onto the device via SD card, and selected for playback with character LCD and rotary knob.

The software transposes the full MIDI music spectrum of a particular track into a 25-note version compatible with the xylophone. Considering that a piano typically has 88 keys, some musical concessions are needed to produce a recognizable playback, but overall it’s an enjoyable musical experience.

Perhaps most remarkable about this project is the documentation. If you want to build your own, everything you need to know is available online, and the no-solder approach makes this project very accessible. Most of the write-up happened some years ago, and we’re really interested to see what improvements have been made since.

The robotic xylophone is reminiscent of these automatic tubular bells from some time ago. These musical hacks can be particularly inspiring, and we can’t wait to see more.

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Travel Guitar Hacked With Digital FX Setup

January 14, 2022 by Lewin Day 8 Comments

[Courcirc8] was a big fan of the ALP AD-80, with the travel guitar being a surprisingly competent instrument despite its folding form-factor. However, the onboard headphone amp left something to be desired, so it was time to get hacking.

To achieve better audio output, [courcirc8] decided to purchase an iRig HD 2 guitar interface, and installed it inside the body of the compact guitar. The original volume pot on the guitar was instead spliced into the iRig circuit, and a switch hooked up to allow the guitar to output clean tones to an amp or the digital audio output of the iRig instead. It’s a tight fit inside, but it all nestles in there rather neatly when finished.

The result is a compact guitar that has a capable digital FX platform built in to the body; all one has to do is hook up a smartphone to gain access to a broad selection of software effects. It makes the guitar much more of a Swiss Army knife when playing on the road.

We’ve seen others before installing guitar effects into the instrument itself; it remains perhaps one of the best ways a hacker can express themselves with a completely individual instrument!

Artist operating artistic visualizer with MIDI keyboard

Synth And Visualizer Combo Has Retrocomputing Vibe

January 11, 2022 by Donald Papp 7 Comments

[Love Hultén]’s latest piece of interactive art is the SYNTH#BOI, a super-clean build with something of the semi-cyberdeck, semi-vintage computing vibe to it. The device is a combination synthesizer and visualizer, with a 15-inch display, MIDI keyboard, and based on an Intel NUC i5 small form factor PC.

There are not many details about the internal workings of the device, but the high quality of the build is very evident. Photos show a fantastic-looking enclosure with clean lines and sharp finish; it’s a reminder that careful measuring and attention to detail can be the difference between something that looks like a hack job, and something that looks like a finished product.

Watch the SYNTH#BOI in action in the video, embedded below. And if the name [Love Hultén] seems familiar, it’s probably because we featured his VOC-25 “Pink Denture Synth”, a concept instrument with a decidedly memorable design of its own.

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HitClips Custom Cartridge Hack Will Never Give Up, Let Down, Or Turn Around

January 10, 2022 by Ryan Flowers 11 Comments

In August 2000, Tiger Electronics released HitClips: Music cartridges and players designed to easily share 60 second low quality Clips of a youngster’s favorite Hits. Various players were available, and individual cartridges were inexpensive enough to collect. And it’s these toy music players that [Guy Dupont] has been hacking quite successfully on as you can see in the video after the break and on [Guy]’s Hackaday.io page.

[Guy]’s main goal was to make cartridges of his own that could not just hold more music than the short clips in the commercially made product, but could make use of modern technology that has matured since HitClips came onto the scene more than 20 years go.

The project’s components are relatively simple, but beautifully executed. An ATTINY84 didn’t work out, so a SAM D09 controller was put it place to to read files from a microSD card and translate the WAV file into the HitClips player’s format. 3d printed cartridges and custom PCB’s complete the hack, ensuring that you can use any of the many HitClips players to play something new for a change.

The end result is quite good, considering that it’s still just 8 bit audio on a 20 year old toy player. Tiger Electronics made another toy that’s quite popular with hackers of the musical kind.

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