A 100-Year-Old Electronic Musical Instrument Brought Back To Life

In the early years of electrification, when electricity was beginning to shape the modern world, this new technology was being put to use in many more places than turning motors and providing lighting. Some things we can see as obvious missteps like electrified corsets marketed as health tonics or x-ray treatments for eye strain, but others ended up being fascinating bits of technology with interesting uses, many of which have been largely forgotten since. This 100-year-old musical instrument is squarely in the latter category, and this build brings the sound of it back to life.

The instrument was called the Luminaphone and was originally built by [Harry Grindell Matthews]. Of course, this was an age before transistors and many other things we take for grated, so it has some quirks that we might not otherwise expect from a musical instrument. The device generated sound by shining a series of lights through a perforated rotating disc at a selenium cell. The selenium cell was an early photoresistor, generating current corresponding to the amount of light falling on it. A keyboard activated different lights, shining on areas of the disc with different numbers of holes, causing differing sounds to be produced by the instrument.

The recreation was built by [Nick Bild] and uses a laser diode as a stand-in for the rotating disc, but since it can be modulated in a similar way the idea is that the photodiode used as a receiver would generate a similar sound. The recreation sounds a bit like a video game from the 8-bit era, but with no recordings or original Luminaphones surviving to the present day we may never know how accurate it is. There are some other electronic instruments still around today, though, and plenty of ways of DIY-ing their sound like this project which recreates the tonewheels of the classic Hammond organ.

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A light-dependent resistor detects cacti in the Google Chrome Offline Dinosaur game.

Jump Cacti With An LDR And A Pico

By now, probably everyone is familiar with the “You’re Offline” dinosaur that stars in Google’s T. Rex game. You know — jump cacti, avoid pterodactyls. Repeat until you lose, or, we suppose, make the leaderboard. Well, what if you theoretically couldn’t lose? That’s kind of the idea behind [Bas BotBerg]’s cactus detection-and-avoidance scheme (translated from Dutch).

Like many of us, [Bas] firmly believes that repetitive tasks should be automated, and that includes the controls of the famous T. Rex. Since the cacti are always dark gray and appear along the same plane, it’s easy to register the difference between cacti and screen electronically. In order to accomplish this, [Bas] is using a light-dependent resistor and a pull-up resistor to create a resistance bridge, which is then connected to an analog input pin on a Raspberry Pi Pico.

But [Bas] didn’t do this just to cheat at Offline Dinosaur. Really! It’s for educational purposes, to get people comfortable with embedded processing, sensors, and interfaces between different devices. Check it out in brief action after the break.

Once they get familiar with these concepts, maybe introduce the ESP32 version of Offline Dinosaur.

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Photoresistor-based Single Pixel Camera

[Hugh] has been going back through episodes of the Hackaday podcast, and Elliot mentioned in episode 67 that it can often be inspiring to go back through the archives of Hackaday to find ideas for new projects. Well, he did just that and came across a single-pixel camera made using an infrared photodiode. He decided to try and hack together his own single-pixel camera, but this time on the cheap and using an ever simpler component – a photoresistor!

His description of the project tickled me – “I’ve used an ESP32, MicroPython, two servos, a peanut butter jar lid, a toilet paper roll, a paper towel roll, magnets and scrap wood for this version.” That’s certainly a much simpler bill of materials than the original (which was written up by Hackaday way back in 2015), which used a nice metal frame to hold everything together. However, there’s absolutely nothing wrong with improvising with things you happen to have to hand.

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Photoresistors Provide Air Gap Data Transfer, Slowly

One of the simplest ways of keeping a computer system secure is by using an air gap — that is, never actually connecting the system to the network. This can often include other peripherals like USB drives and other removable storage as well, so getting information to and from secure (or compromised) systems behind air gaps can often present a challenge. But assuming you have local access to the computer and your parts bin handy, these optical solutions from [Nikolay] can allow  data transfer to or from such off-line computers.

[Nikolay]’s specific use case for this project is to transfer small amounts of information to or from computers that may be compromised in some way, or computers that might otherwise be dangerous to connect to other equipment. There’s actually several methods described in the project, the first involves temporarily attaching a photoresistor to the computer’s screen which has been wired into the remains of a USB keyboard. A script running on the compromised machine translates data into a series of white and black squares. The sensors can detect these patterns much like playing Duck Hunt on an old CRT television and transmit the data across the air gap with reasonable certainty nothing harmful crossed with it.

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Rotary Time Tracker Puts A New Spin On Productivity

Like many of us, [quincy] feels the distracting pull of non-work programs on what has become a mixed-use computer. So what’s the answer to the puzzle of work-life balance? We’re not sure, but time management and keeping track of tasks will probably get you most of the way there. The only problem is that keeping track of these things is boring and tedious and way too easy to forget, even for the fun tasks.

Similar commercial gadgets exist to serve this time-tracking purpose, but [quincy] wanted something much cooler that would work the same way: turn the indicator to the current task, and the status gets recorded on a computer. Rather than some smart polygon with informative stickers on each face à la the Timeflip2, [quincy] built a rotary task manager that serves the same purpose, but does it with magnets.

Our favorite part aside from the magnets has to be the clever binary encoding work. [quincy] is using three photoresistors and a single green LED to create a 3D-printed gray encoder that sidesteps the need to ever flip two bits at once. An Arduino takes care of reading the 3-bit code and converting it back into a decimal. There are more updates to come, including the main .ino file, but you can start printing the pieces while you wait.

If you have trouble staying on task, maybe you need a Pomodoro timer. We’ve seen a few over the years, ranging from the minimal to the sculptural.

Co41D 2020 MIDI Theremin Sounds Pretty Sick

As the pandemic rages on, so does the desire to spend the idle hours tinkering. [knaylor1] spent the second UK lockdown making a sweet Theremin-inspired noise machine with a low parts count that looks like a ton of fun.

It works like this: either shine some light on the photocells, cover them up, or find some middle ground between the two. No matter what you do, you’re going to get cool sounds out of this thing.

The photocells behave like potentiometers that are set up in a voltage divider. An Arduino UNO takes readings in from the photocells, does some MIDI math, and sends the serial data to a program called Hairless MIDI, which in turn sends it to Ableton live.

[knaylor1] is using a plugin called TAL Noisemaker on top of that to produce the dulcet acid house tones that you can hear in the video after the break.

If you’ve never played with light-dependent resistors before, do yourself a favor and spend a little bit of that Christmas cash on a variety pack of these things. You don’t even need an Arduino to make noise, you can use them as the pots in an Atari Punk console or make farty square waves with a hex inverting oscillator chip like the CD40106. Our own [Elliot Williams] once devoted an entire column to making chiptunes.

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Bolt-On Clog Detection For Your 3D Printer

Desktop 3D printing technology has improved by leaps and bounds over the last few years, but they can still be finicky beasts. Part of this is because the consumer-level machines generally don’t offer much in the way of instrumentation. If the filament runs out or the hotend clogs up and stops extruding, the vast majority of printers will keep humming along with nothing to show for it.

Looking to prevent the heartache of a half-finished print, [Elite Worm] has been working on a very clever filament detector that can be retrofitted to your 3D printer with a minimum of fuss. The design, at least in its current form, doesn’t actually interface with the printer beyond latching onto the part cooling fan as a convenient source of DC power. Filament simply passes through it on the way to the extruder, and should it stop moving while the fan is still running (indicating that the machine should be printing), it will sound the alarm.

Inside the handy device is a Digispark ATtiny85 microcontroller, a 128 x 32  I2C OLED display, a buzzer, an LED, and a photoresistor. An ingenious 3D printed mechanism grabs the filament on its way through to the extruder, and uses this movement to alternately block and unblock the path between the LED and photoresistor. If the microcontroller doesn’t see the telltale pulse after a few minutes, it knows that something has gone wrong.

In the video after the break, [Elite Worm] fits the device to his Prusa i3 MK2, but it should work on essentially any 3D printer if you can find a convenient place to mount it. Keep a close eye out during the video for our favorite part of the whole build, using the neck of a latex party balloon to add a little traction to the wheels of the filament sensor. Brilliant.

Incidentally, Prusa tried to tackle jam detection optically on the i3 MK3 but ended up deleting the feature on the subsequent MK3S since the system proved unreliable with some filaments. The official line is that jams are so infrequent with high-quality filament that the printer doesn’t need it, but it does seem like an odd omission when even the cheapest paper printer on the market still beeps at you when things have run afoul.

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