Know Audio: Mixtapes, Tape Loops, And Razor Blades

December 20, 2021 by 16 Comments

In our no-nonsense journey through the world of audio technology we’ve so far have looked at digital audio and the vinyl disk recording. What’s missing? Magnetic tape, the once-ubiquitous recording medium that first revolutionised the broadcast and recording industries in the mid-20th-century, and went on to be a mainstay of home audio before spawning the entire field of personal audio. Unless you’re an enthusiast or collector, it’s likely you won’t have a tape deck in your audio setup here in 2021 and you’ll probably be loading your 8-bit games from SD card rather than cassette, but surprisingly there are still plenty of audio cassettes released as novelties or ephemeral collectables.

The Device That Made The Sound Of The Latter Half Of The 20th Century

"Like a travelling razor blade", a Blattnerphone steel-strip tape recorder at the BBC in 1937. Douglas Hallam, Jr., Public domain.
“Like a travelling razor blade”, a Blattnerphone steel-strip tape recorder at the BBC in 1937. Douglas Hallam, Jr., Public domain.

The first magnetic recordings were made directly on metal wires, but metal fatigues as it bends. By coating a flexible plastic tape in ferrous particles, the same simple technique of laying down an audio signal as variations in the magnetic field could be made smaller, lighter, and more robust. But the key to the format’s runaway success is the technical advancements that differentiate those 1950s machines from their wire recorder ancestors.

Whether it is a humble cassette recorder or a top-end studio multitrack, all tape recorders are very similar. There are two reels that hold the tape: the playback reel that houses the recording, and the take-up reel that stores the tape as it plays in the machine. The take-up reel is lightly driven to run faster than the tape speed, and the playback reel has a slight braking force to keep the tape under tension at all times. Continue reading “Know Audio: Mixtapes, Tape Loops, And Razor Blades” →

Building MS-DOS From Scratch Like It’s 1983

December 20, 2021 by 52 Comments

Building a complete operating system by compiling its source code is not something for the faint-hearted; a modern Linux or BSD distribution contains thousands of packages with millions of lines of code, all of which need to be processed in the right order and the result stored in the proper place. For all but the most hardcore Gentoo devotees, it’s way easier to get pre-compiled binaries, but obviously someone must have run the entire compilation process at some point.

What’s true for modern OSes also holds for ancient software such as MS-DOS. When Microsoft released the source code for several DOS versions a couple of years ago, many people pored over the code to look for weird comments and undocumented features, but few actually tried to compile the whole package. But [Michal Necasek] over at the OS/2 Museum didn’t shy away from that challenge, and documented the entirely-not-straightforward process of compiling DOS 2.11 from source.

The first problem was figuring out which version had been made available: although the Computer History Museum labelled the package simply as “MS-DOS 2.0”, it actually contained a mix of OEM binaries from version 2.0, source code from version 2.11 and some other stuff left from the development process. The OEM binaries are mostly finished executables, but also contain basic source code for some system components, allowing computer manufacturers to tailor those components to their specific hardware platform.

Compiling the source code was not trivial either. [Michal] was determined to use period-correct tools and examined the behaviour of about a dozen versions of MASM, the assembler likely to have been used by Microsoft in the early 1980s. As it turned out, version 1.25 from 1983 produced code that most closely matched the object code found in existing binaries, and even then some pieces of source code required slight modifications to build correctly. [Michal]’s blog post also goes into extensive detail on the subtle differences between Microsoft-style and IBM-style DOS, which go deeper than just the names of system files (MSDOS.SYS versus IBMDOS.COM).

The end result of this exercise is a modified DOS 2.11 source package that actually compiles to a working set of binaries, unlike the original. And although this does not generate any new code, since binaries of DOS 2.11 have long been available, it does provide a fascinating look into software development practices in an age when even the basic components of the PC platform were not fully standardized. And don’t forget that even today some people still like to develop new DOS software.

Is Cloud Seeding Good, Bad, Or Ugly?

December 20, 2021 by 34 Comments

The Chinese Communist Party celebrated its centenary on the 1st of July, 2021. For such a celebration, clear skies and clean air would be ideal. For the capable nation-state, however, one needn’t hope against the whims of the weather. One can simply control it instead!

A recent paper released by Tsinghua University indicated that China had used cloud seeding in order to help create nicer conditions for its 100-year celebration. Weather modification techniques have been the source of some controversy, so let’s explore how they work and precisely what it was that China pulled off.

Continue reading “Is Cloud Seeding Good, Bad, Or Ugly?” →

An All In One Cube PC For A 1990s That Never Quite Happened

December 20, 2021 by 12 Comments

When a particular device or appliance is evoked, there comes with it a set of expectations over what it might look like. A toaster, a camera, a washing machine, or a PC, will all have their own accepted form factors, and it’s rare that a manufacturer is adventurous enough to venture outside them. In the world of PCs there was a brief flowering of this type of creativity through the 1990s, and it’s that time which [ikeji]’s cube PC squarely fits in. It’s a 3D printed PC with a built-in display, keyboard, and printer, and while some might categorize it as a cyberdeck we’d say it goes further, we could easily imagine a slightly more polished version being an object of desire back when a powerful machine carried an 80486.

Inside it’s no slouch, packing an AMD Ryzen 7 Pro on a Mini-ITX motherboard, and while the display is a mere 7-incher it fits neatly behind the fold-down keyboard. The thermal printer is maybe more of a toy, but it’s good to find that even a bleeding-edge motherboard still has a serial port on it somewhere that it can talk to.

While the build undoubtedly has a few home-built rough edges we like the idea, echoing as it does those all-in-ones from the CRT era. Unless you have a handy Minitel terminal you won’t find much like it.

A Particularly Festive Chip Decapping

December 20, 2021 by 16 Comments

As we approach the moment in the year at which websites enter a festive silly season of scrambling to find any story with a festive angle, we’re pleased to see the ever-reliable [Ken Shirriff] has brought his own take on Christmas tech to the table with a decapping of the UM66T melody chip that has graced so many musical greeting cards.

The surprise in this age of ubiquitous microcontrollers is that this is not a smart device; instead it’s a single-purpose logic chip whose purpose is to step through a small ROM containing note values and durations, driving a frequency generator to produce the notes themselves. The frequency generator isn’t the divider chain from the RC oscillator that we might expect, instead it’s a shift register arrangement which saves on the transistor count.

Although the UM66 is a three-pin device, there are a few other pins on the die. These are likely to be for testing. As a 30+ year old product its design may be outdated in 2021, but it’s one of those chips that has survived without being superseded because it does its task without the need for improvement. So when you open a card and hear the tinny tones of a piezo speaker this holiday season, spare a thought for the ingenuity of the design behind the chip that makes it all possible.

A wooden device with an LED display and speakers

The Inspirer Keeps Your Mood Up With Inspirational Quotes And Soothing Music

December 19, 2021 by 2 Comments

While some people enjoy the cold weather and long, dark nights in the Northern Hemisphere these days, others may find it hard to keep a positive mindset all through the winter. [Michael Wessel] decided he needed to do something about that and came up with The Inspirer, a desktop display that shows inspirational quotes and plays soothing music.

The design is deliberately bare-bones: a strip of wood, standing upright thanks to two metal brackets, onto which a bunch of components have been screwed, glued and taped. The actual display consists of a row of 14-segment LED modules that can show basic alphanumeric characters; these displays emit white light, but [Michael] added a red color filter in front to give them a more “retro” look.

This device is fully off-grid, so no Internet connection issues will disrupt your flow. A huge database of quotes and a selection of music tracks are stored on a pair of micro SD cards; an MP3 player module handles the music while an Arduino picks a quote, drives the display, and reads the buttons. You can select quotes based on a certain theme: examples include friendship, gardening, money, and love. But if you’re open to anything, you can just set it to “random” and get something from any of the 120 categories.

[Michael]’s simple and straightforward design should hopefully prove inspirational to many hardware enthusiasts. But if you’re looking for something more advanced, we featured a neat pomodoro timer that displays quotes a few weeks ago. Of course, this being Hackaday, we’ve also seen a clock based on literary quotes.

Continue reading “The Inspirer Keeps Your Mood Up With Inspirational Quotes And Soothing Music” →