Touch Tone MIDI Phone And Vocoder Covers Daft Punk

September 6, 2022 by Donald Papp 3 Comments

[poprhythm]’s Touch Tone MIDI Phone is a fantastic conversion of an old touch tone phone into a MIDI instrument complete with intact microphone, but this project isn’t just about showing off the result. [poprhythm] details everything about how he interfaced to the keypad, how he used that with an Arduino to create a working MIDI interface, and exactly how he decided — musically speaking — what each button should do. The LEDs on the phone are even repurposed to blink happily depending on what is going on, which is a nice touch.

Of course, it doesn’t end there. [poprhythm] also makes use of the microphone in the phone’s handset. Since the phone is now a MIDI instrument with both a microphone and note inputs, it’s possible to use them together as the inputs to vocoder software, which he demonstrates by covering Around the World by Daft Punk (video).

We love how [poprhythm] explains how he interfaced to everything because hardware work is all about such details, and finding the right resources. Here’s the GitHub repository for the Arduino code and a few links to other resources.

We have seen MIDI phone projects before, and each one is always unique in its own way: here’s a different approach to converting a keypad phone to MIDI, and this rotary pulse-dial phone went in a completely different direction with the phone itself completely unmodified, using only external interfacing.

You can admire [poprhythm]’s Touch Tone MIDI Phone in action in the short videos embedded below, with each one showing off a different aspect of the build. It’s great work!

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C64 Turned Theremin With A Handful Of Parts

August 30, 2022 by Lewin Day 7 Comments

The theremin is popular for its eerie sound output and its non-contact playing style. While they’re typically built using analog hardware, [Linus Åkesson] decided to make one using the venerable Commodore 64.

The instrument works by measuring the capacitance between its two antennas and the Earth. As these capacitances are changed by a human waving their hands around near the respective pitch and volume antennas, the theremin responds by changing the pitch and volume of its output.

In this case, the humble 555 is pressed into service. It runs as an oscillator, with its frequency varying depending on the user’s hand position. There’s one each for pitch and volume, naturally, using a clamp and spoon as antennas. The C64 then reads the frequency the 555s are oscillating at, and then converts these into pitch and volume data to be fed to the SID audio chip.

[Linus Åkesson] demonstrates the build ably by performing a slow rendition of Amazing Grace. The SID synthesizer chip in the C64 does a passable job emulating a theremin, used here with a modulated pulse wave sound. It’s an impressive build and one we fully expect to see at a big chiptune show sooner rather than later. We’re almost surprised nobody came out with a C64 Theremin cartridge back in the day.

We’ve seen other fancy theremin-inspired builds recently too, like this light-based design.

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Reactive Load For Amplifiers Teaches Lessons About Inductors

August 24, 2022 by Bryan Cockfield 26 Comments

The sound produced by any given electric guitar is shaped not just by the instrument itself but by the amplifiers chosen to make that sound audible. Plenty of musicians swear by the warm sound of amplifiers with vacuum tube circuits, but they do have some limitations. [Collin] wanted to build a reactive load for using tube amps without generating a huge quantity of sound, and it resulted in an interesting project that also taught him a lot about inductors.

The reactive load is essentially a dummy load for the amplifier that replaces a speaker with something that won’t produce sound. Passive loads typically use resistor banks but since this one is active, it needs a very large inductor to handle the amount of current being produced by the amplifier. [Colin] has also built a headphone output into this load which allows it to output a much smaller quantity of sound to a headset while retaining the sound and feel of the amplifier tubes, and it additionally includes a widely-used tone control circuit as well.

There’s a lot going on in the design of the circuitry for this amplifier load, including a lot of research into low-frequency inductors that can handle a significant amount of current. [Collin] eventually ended up winding his own, but the path he took to it was long and winding. There’s a lot of other circuit theory discussed as well especially with regards to the Baxandall EQ that he built into it as well. And, if you’d like to learn more about tube amplifiers in general, take a look at this piece which notes one of the best stereo amps ever produced.

PicoStepSeq Is Small But Perfectly Formed

August 20, 2022 by Jenny List 18 Comments

The Raspberry Pi Pico is what you might call the board of the moment, thanks to its combination of affordability, features, and continued availability during the component shortage. We have seen plenty of great projects using it, and the latest to float past is [todbot]’s PicoStepSeq, an extremely compact MIDI sequencer.

All the components are mounted on a PCB, with the sequencer’s eight steps selected by a row of buttons with integrated LEDs. The interface is via an SSD1306 OLED, and there is also a rotary encoder. Software comes courtesy of CircuitPython, and the output is delivered via a 3.5 mm TRS jack. Finally the whole is wrapped in a 3D printed enclosure.

The result is a sequencer that could almost be a product in its own right, and we think anyone whose interests lie in electronic music should find straightforward enough to build. All the files and information required to build your own can be found in the linked repository, and he’s placed a Tweet with a video online which we’ve embedded below the break.

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LCD Monitor Plays The Hits

August 18, 2022 by Al Williams 1 Comment

In the old days, it wasn’t uncommon to put an AM radio near a computer or a monitor and deliberately cause interference to have a crude form of sound generation. Did you miss out on that? No! Thanks to [luambfb] you can now do the same trick with a common LCD monitor. You’ll need the horizontal refresh rate of the monitor in question.

Of course, doing it is somewhat less interesting than learning how it works. The effect relies on the fact that the LCDs emit signals as it refreshes a row. A black row emits relatively low energy while a white row emits more. Grayscale… well, you get the idea. Continue reading “LCD Monitor Plays The Hits” →

Is 3D Printing Up To A Turntable?

July 23, 2022 by Jenny List 20 Comments

Thanks to a feature by Prusament because it uses their filament, we’ve been interested to read about the SongBird turntable from the British outfit Frame Theory (Note: at time of writing, they have an expired certificate). It’s a commercial product with an interesting twist for the Hi-Fi business: buy the completed turntable or buy a kit of parts and print the rest yourself.

We’re always interested to see new things here at Hackaday but we’re not in the business of promoting commercial products without a tech angle. This turntable has us interested then not because it happens to be 3D printed but because it’s instantly raised our curiosity over how suitable 3D printing is as a medium for a high quality audio component. Without descending into audiophile silliness we cannot overstate the effect that rigidity and mass of turntable components has on its audio quality. Take a look at this one we featured in the past for an extreme example.

So looking more closely at the design, we find that the chassis is aluminium, which makes sense given its visibly thin construction. Close examination of the photos on their site also reveals the tonearm to be made of carbon fibre tube, so it’s clear that they’ve put some effort into making a better turntable rather than a novelty one. This does raise the question though: manufacturing practicalities aside could you 3D print the whole thing? We think that a 3D printed chassis could replace the aluminium one at the cost of much more bulk and loss of the svelte looks, but what about the tonearm? Would one of the carbon-fibre-infused filaments deliver enough stiffness? It would be particularly interesting we think, were someone to try.

Restoring $5 Busted Synthesizer Made Easy, Thanks To Thermal

July 16, 2022 by Donald Papp 19 Comments

[D. Scott Williamson] paid $5 for a Roland JV-30 synthesizer at a garage sale. Score! There was only one catch: it didn’t work and didn’t include the power supply. Luckily, restoring it was made easier by breaking out a thermal camera.

As mentioned, the keyboard was missing a 9 VDC power supply (rated 800 mA) with a center-negative barrel connector. Slightly oddball, but nothing an enterprising hacker can’t deal with. After supplying power with a bench supply, not only did the keyboard not come to life, but the power supply clamped the current draw at 1.5 A! Something was definitely not right.

This shorted glass-bodied diode might look normal to the naked eye, but thermal imaging makes it clear something’s amiss.

Inside, there was no visible (or olfactory) sign of damage, but looking closer revealed that a little SMT capacitor by the power connector was cracked in two. Fixing that didn’t bring the keyboard to life, so it was time to break out the thermal imager. Something was soaking up all that current, and it’s a fair bet that something is getting hot in the process.

The culprit? The reverse polarity protection diode was shorted, probably as a result of damage by an inappropriate power supply or a surge of some kind. Replacing it resulted in a working keyboard! Not bad at all for $5, a diode, an SMT cap, and a little workbench time. The finishing touch was replacing a missing slider knob, which took some work in OpenSCAD and a 3D printer. Overall, not bad!

Thermal imaging used to be the stuff of staggering price tags, but it’s downright accessible these days, and makes it easy to spot things that are hot when they shouldn’t be. And if a thermal camera’s lens isn’t what you think it should be? It’s even possible for a sufficiently motivated and knowledgeable hacker to modify those.