The Tape Speed Keyboard

August 4, 2025 by Bryan Cockfield 10 Comments

For those who experienced any part of the 1960s, even if it’s just experiencing the music from that era here in the future, the sound of the Mellotron is immediately recognizable. The Moody Blues were famous for using the tape-based instrument, and the Beatles and David Bowie produced hits with it as well. It’s haunting sounds are still highly prized today, but the complexity, cost, and maintenance requirement for the tape loops and other moving parts can put many musicians off from owning one. But [Japhy Riddle] has built an instrument without these downsides called the Tape Speed Keyboard.

Unlike the Mellotron which used a tape loop for each of its keys, the Tape Speed Keyboard uses only a single cassette tape. As the name implies, it changes the pitch of the sound by modulating the speed of the single tape housed in its own tape deck. The keyboard itself started off life as a Casio MT-35 but since this is a completely analog instrument, it was rewired so each key is connected to a potentiometer whose output voltage is tuned to a specific tape speed. [Japhy] reports that this is similar to tuning an analog piano and the process can be equally temperamental.

With everything electronic working, [Japhy] turned to making this a more acceptable musical instrument. Predictably, turning the motor on and off for each key press came with a bit of delay, causing the sound to come out goofy and muddy. To solve this problem he changed the design to make the tape play continuously rather than start and stop for a key press, and then modified other keys to be on-off switches for sound output. Since cassette tapes have two sides, he can also play either of two sounds in this way.

With the final polish on, the Tape Speed Keyboard is able to produce completely unique compositions that separate it from even the venerable Mellotron. Be sure to check out the video linked below to hear its sound. There have been plenty of other musical projects based around tape decks as well, including this one inspired by the original Mellotron and this tape deck-based guitar effects pedal.

Thanks to [splashbun] for the tip!

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A sine wave and triangle wave on a black background

2025 One Hertz Challenge: Op-Amp Madness

July 31, 2025 by Adam Zeloof 7 Comments

Sometimes, there are too many choices in this world. My benchtop function generator can output a sine, square, or saw wave anywhere from 0.01 Hz up to 60 MHz? Way too many choices. At least, that’s what we suspect [Phil Weasel] was thinking when he built this Analog 1 Hz Sinewave Generator.

Rendering of a PCB — A KiCad rendering of [Phil]’s design

[Phil]’s AWG (which in this case stands for Anything as long as it’s a 1 Hz sine Wave Generator) has another unique feature — it’s built (almost) entirely with op-amps. A lot of op-amps (37, by our count of the initial schematic he posted). His design is similar to a Phased Locked Loop (PLL) and boils down to a triangle wave oscillator. While a 1 Hz triangle wave would absolutely satisfy judges of the One Hertz Challenge, [Phil] had set out to make a sine wave. Using a feedback loop and some shaping/smoothing tricks (and more op-amps), he rounded off the sharp peaks into a nice smooth sine wave.

Sometimes we make things much more complicated than we need to, just to see if we can. This is one of those times. Are there much simpler ways to generate a sine wave? Yes — but not exclusively using op-amps! This entry brings stiff competition to the “Ridiculous” category of the 2025 One Hertz Challenge.

Super8 Camera Brought To The Modern World

June 30, 2025 by Bryan Cockfield 19 Comments

Certain styles of photography or videography immediately evoke an era. Black-and-white movies of flappers in bob cuts put us right in the roaring 20s, while a soft-focused, pastel heavy image with men in suits with narrow ties immediately ties us to the 60s. Similarly, a film shot at home with a Super 8 camera, with its coarse grain, punchy colors, and low resolution brings up immediate nostalgia from the 80s. These cameras are not at all uncommon in the modern era, but the cartridges themselves are definitely a bottleneck. [Nico Rahardian Tangara] retrofitted one with some modern technology that still preserves that 80s look.

The camera he’s using here is a Canon 514XL-S that was purchased for only $5, which is a very common price point for these obsolete machines, especially since this one wasn’t working. He removed all of the internal components except for a few necessary for the camera to work as if it still was using film, like the trigger mechanism to allow the camera to record. In the place of tape he’s installed a Raspberry Pi Zero 2W and a Camera Module 3, so this camera can record in high definition while retaining those qualities that make it look as if it’s filmed on an analog medium four decades ago.

[Nico] reports that the camera does faithfully recreate this early era of home video, and we’d agree as well. He’s been using it to document his own family in the present day, but the results he’s getting immediately recall Super 8 home movies from the 80s and early 90s. Raspberry Pis are almost purpose-built for the task of bringing older camera technology into the modern era, and they’re not just limited to video cameras either. This project put one into an SLR camera from a similar era.

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NES Zapper Becomes Telephone

May 25, 2025 by Bryan Cockfield 9 Comments

Although there was a time in the 80s (and early 90s for fans of the SuperScope) where light guns were immensely popular, with games like DuckHunt cultural touchstones, their time in the video game world has largely come to an end. We might occasionally pick up a Zapper for the NES and play this classic out of nostalgia, but plenty of people are looking for other things that these unique video game controllers can do instead. [Nick] has turned one of his old NES peripherals into a wireless phone.

The way the original Zapper worked was by looking for a certain pattern of pixels that displayed for a fraction of a second whenever the trigger was pulled. Bypassing the anti-cheat mechanism that looks only for qualities of light coming from CRT screens of the day effectively turns the light gun into an analog light sensor which is used for receiving the audio from the phone’s base station via a laser. Of course there were no microphones present within the original hardware so one is added, wiring its output to another laser that communicates to the base station. With the light gun pointed directly at this base station, audio is communicated back and forth by varying the strengths of these small lasers and listening to them on the other end with photodiodes.

[Nick] does point out that this isn’t a great phone, largely because it needs to be pointed exactly at the right spot to work at all, although we do agree that it’s an interesting project that demonstrates what the original hardware could do with a few of its limitations removed. There are a few other ways of bringing these devices into the modern world, with one of our favorites being this laser pointer with additional hardware from a Wiimote that could also function as a mouse.

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Five Oddest Op Amp Applications

May 6, 2025 by Al Williams 25 Comments

You think of op amps as amplifiers because, no kidding, it is right in the name. But just like some people say, “you could do that with a 555,” [Doctor Volt] might say, “you can do that with an op amp.” In a recent video, you can see below, he looks at simulations and breadboards for five applications that aren’t traditional amplifiers.

Of course, you can split hairs. A comparator is sort of an amplifier with some very specific parameters, but it isn’t an amplifier in the classic sense.

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Supercon 2024: A Hacker’s Guide To Analog Design In A Digital World

May 6, 2025 by Navarre Bartz 9 Comments

We often think of analog computing as a relic of the past, room-sized monstrosities filled with vacuum tubes doing their best to calculate Monte Carlo simulations or orbital velocities. Analog isn’t as dead as it might seem though, and analog mix signal design engineer [Nanik Adnani] gave us a crash course on analog circuits at Supercon 2024.

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Crossing Commodore Signal Cables On Purpose

April 29, 2025 by Bryan Cockfield 19 Comments

On a Commodore 64, the computer is normally connected to a monitor with one composite video cable and to an audio device with a second, identical (although uniquely colored) cable. The signals passed through these cables are analog, each generated by a dedicated chip on the computer. Many C64 users may have accidentally swapped these cables when first setting up their machines, but [Matthias] wondered if this could be done purposefully — generating video with the audio hardware and vice versa.

Getting an audio signal from the video hardware on the Commodore is simple enough. The chips here operate at well over the needed frequency for even the best audio equipment, so it’s a relatively straightforward matter of generating an appropriate output wave. The audio hardware, on the other hand, is much less performative by comparison. The only component here capable of generating a fast enough signal to be understood by display hardware of the time is actually the volume register, although due to a filter on the chip the output is always going to be a bit blurred. But this setup is good enough to generate large text and some other features as well.

There are a few other constraints here as well, namely that loading the demos that [Matthias] has written takes so long that the audio can’t be paused while this happens and has to be bit-banged the entire time. It’s an in-depth project that shows mastery of the retro hardware, and for some other C64 demos take a look at this one which is written in just 256 bytes.

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