Hackaday Links: August 24, 2025

August 24, 2025 by Dan Maloney 9 Comments

“Emergency Law Enforcement Officer Hologram program activated. Please state the nature of your criminal or civil emergency.” Taking a cue from Star Trek: Voyager, the Seoul Metropolitan Police Agency is testing a holographic police officer, with surprisingly — dare we say, suspiciously? — positive results. The virtual officer makes an appearance every two minutes in the evening hours in a public park, presumably one with a history of criminal activity. The projection is accompanied by a stern warning that the area is being monitored with cameras, and that should anything untoward transpire, meat-based officers, presumably wearing something other than the dapper but impractical full-dress uniform the hologram sports, will be dispatched to deal with the issue.

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Listening To Ethernet Via Eurorack

July 26, 2025 by Lewin Day 9 Comments

Ethernet is how we often network computers together, particularly when they’re too important to leave on a fussy WiFi connection. Have you ever thought about listening to Ethernet signals, though? Well, you totally could, with the NSA selector from [wenzellabs].

The NSA selector is a Eurorack module, designed for use as part of a larger modular synthesizer. There are lots of fun jokes and references on the PCB, but the front panel really shows you what this module is all about. It’s got a pair of RJ45 jacks, ready to receive your Ethernet cables through which data is flowing. They’re paired with a single audio output jack. “Any bit on the network will be sent to the audio output,” [wenzellabs] explains.

The device operates in a relatively simple fashion. Network traffic from one jack is forwarded to the other, unmodified. However, it’s also spat out to a simple digital-to-analog converter and turned into audio. This thing doesn’t play digital audio formats or anything like that—it just turns raw Ethernet signalling into audible noise.

Raw signal noises might not sound very appealing, but let’s be real here. If you liked nice sounds, you wouldn’t be into Eurorack. Skip to 25:46 in the video below if you just want to hear the final product.

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Designing An FM Drum Synth From Scratch

April 17, 2025 by Dan Maloney 14 Comments

How it started: a simple repair job on a Roland drum machine. How it ended: a scratch-built FM drum synth module that’s completely analog, and completely cool.

[Moritz Klein]’s journey down the analog drum machine rabbit hole started with a Roland TR-909, a hybrid drum machine from the mid-80s that combined sampled sounds with analog synthesis. The unit [Moritz] picked up was having trouble with the decay on the kick drum, so he spread out the gloriously detailed schematic and got to work. He breadboarded a few sections of the kick drum circuit to aid troubleshooting, but one thing led to another and he was soon in new territory.

The video below is on the longish side, with the first third or so dedicated to recreating the circuits used to create the 909’s iconic sound, slightly modifying some of them to simplify construction. Like the schematic that started the whole thing, this section of the video is jam-packed with goodness, too much to detail here. But a few of the gems that caught our eye were the voltage-controlled amplifier (VCA) circuit that seems to make appearances in multiple places in the circuit, and the dead-simple wave-shaper circuit, which takes some of the harmonics out of the triangle wave oscillator’s output with just a couple of diodes and some resistors.

Once the 909’s kick and toms section had been breadboarded, [Moritz] turned his attention to adding something Roland hadn’t included: frequency modulation. He did this by adding a second, lower-frequency voltage-controlled oscillator (VCO) and using that to modulate the drum section. That resulted in a weird, metallic sound that can be tuned to imitate anything from a steel drum to a bell. He also added a hi-hat and cymbal section by mixing the square wave outputs on the VCOs through a funky XOR gate made from discrete components and a high-pass filter.

There’s a lot of information packed into this video, and by breaking everything down into small, simple blocks, [Moritz] makes it easy to understand analog synths and the circuits behind them.

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Reviving A Maplin 4600 DIY Synthesizer From The 1970s

March 19, 2025 by Donald Papp 16 Comments

A piece of musical history is the Maplin 4600, a DIY electronic music synthesizer from the 1970s. The design was published in an Australian electronics magazine and sold as a DIY kit, and [LOOK MUM NO COMPUTER] got his hands on an original Maplin 4600 that he refurbishes and puts through its paces.

Inserting conductive pegs is how the operator connects different inputs and outputs.

The Maplin 4600 is a (mostly) analog device with a slightly intimidating-looking layout. It features multiple oscillators, mixers, envelope generators, filters, and a complex-looking patch bay on the right hand side that is reminiscent of a breadboard. By inserting conductive pins, one can make connections between various inputs and outputs.

Internally the different features and circuits are mostly unconnected from one another by default, so the patch board is how the instrument is “programmed” and the connections made can be quite complex. The 4600 is one of a few synthesizer designs by [Trevor Marshall], who has some additional details about on his website.

The video (embedded below) is a complete walk-through of the unit, including its history, quirks, and design features. If you’d like to skip directly to a hands-on demonstrating how it works, that begins around the 10:15 mark.

Synthesizers have a rich DIY history and it’s fascinating to see an in-depth look at this one. And hey, if you like your synths complex and intimidating, do yourself a favor and check out the Starship One.

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RISC-V Microcontroller Lights Up Synth With LED Level Meter

January 10, 2025 by Dan Maloney 8 Comments

The LM3914 LED bar graph driver was an amazing chip back in the day. Along with the LM3915, its logarithmic cousin, these chips gave a modern look to projects, allowing dancing LEDs to stand in for a moving coil meter. But time wore on and the chips got harder to find and even harder to fit into modern projects, what with their giant DIP-18 footprint. What’s to be done when a project cries out for bouncing LEDs? Simple — get a RISC-V microcontroller and roll your own LED audio level meter.

In fairness, “simple” isn’t exactly what comes to mind while reading [svofski]’s write-up of this project. It’s part of a larger build, a wavetable synth called “Pétomane Ringard” which just screams out for lots of blinky LEDs. [svofski] managed to squeeze 20 small SMD LEDs onto the board along with a CH32V003 microcontroller. The LEDs are charlieplexed, using five of the RISC-V chip’s six available GPIO lines, leaving one for the ADC input. That caused a bit of trouble with programming, since one of those pins is needed to connect to the programmer. This actually bricked the chip, thankfully only temporarily since there’s a way to glitch the chip back to life, but only after pulling it out of the circuit. [svofski] recommends adding a five-second delay loop to the initialization routine to allow time to recover if the microcontroller gets into an unprogrammable state. Good tip.

As for results, we think the level meter looks fantastic. [svofski] went for automated assembly of the 0402 LEDs, so the strip is straight and evenly spaced. The meter seems to be quite responsive, and the peak hold feature is a nice touch. It’s nice to know there’s a reasonable substitute for the LM391x chips, especially now that all the hard work has been done.
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The Math Behind The Music Of The 80s

December 11, 2024 by Bryan Cockfield 51 Comments

Although there might have been other music produced or recorded in the 1980s, we may never know of its existence due to the cacophony of all of the various keytars, drum machines, and other synthesized music playing nonstop throughout the decade. There was perhaps no more responsible synthesizer than the Yamaha DX7 either; it nearly single-handedly ushered in the synth pop era. There had been other ways of producing similar sounds before but none were as unique as this keyboard, and for ways beyond just its sound as [Kevin] describes in this write-up.

Part of the reason the DX7 was so revolutionary was that it was among the first accessible synthesizers that was fully digital, meaning could play more than one note at a time since expensive analog circuitry didn’t need to be replicated for multiple keys. But it also generated its tones by using frequency modulation of sine waves in a way that allowed many signals to be combined to form different sounds. While most popular musicians of the 80s used one of the preset sounds of the synthesizer, it could produce an incredible range of diverse sounds if the musician was willing to dig a bit into the programming of this unique instrument.

There were of course other reasons this synthesizer took off. It was incredibly robust, allowing a musician to reliably carry it from show to show without much worry, and it also stood on the shoulders of giants since musicians had been experimenting with various other types of synthesizers for the previous few decades. And perhaps it was at the right place and time for the culture as well. For a look at the goings on inside the chip that powered the device, [Ken Shirriff] did a deep dive into one a few years ago.

Minichord Wants To Help You Find Rad Chord Progressions

November 28, 2024 by Lewin Day 8 Comments

If you’re good at music theory, you can probably find all the chords and progressions you need just by using your fingers and a suitable instrument. For a lot of musicians, though, remembering huge banks of chords can be difficult, and experimenting with combinations can quickly become tedious and tiring. Enter the minichord, a tiny version of the Omnichord synth designed by [Benjamin] that offers to help out by putting all the chords you need a mere button press away.

The minichord is based around the Teensy 4.0, a capable microcontroller platform if ever there was one. It’s paired with a bunch of tactile buttons which are used to tell the Teensy which chord you desire to play. Various combinations of buttons can be used to play more advanced chords, too. There are potentiometers on board as well for volume control, as well as a touch pad for “strumming” arpeggios and other fine control tasks. An online interface allows modifying the presets onboard, too.

[Benjamin] hopes to get the minichord into production; it’s currently in a Seeedstudio competition that could see that happen, based on likes on the project video. The minichord isn’t the only player in this space, of course. The Orchard synth has been making similar waves this week. We’ve seen [Benjamin’s] work before, too. Video after the break. Continue reading “Minichord Wants To Help You Find Rad Chord Progressions” →