Today, it is hard to imagine a world without recorded audio, and for the most part that started with Edison’s invention of the phonograph. However, for most of its history, the phonograph was a one-way medium. Although early phonographs could record with a separate needle cutting into foil or wax, most record players play only records made somewhere else. The problem is, this cuts down on what you can do with them. When offices were full of typists and secretaries, there was the constant problem of telling the typist what to type. Whole industries developed around that problem, including the Dictaphone company.

The issue is that most people can talk faster than others can write or type. As a result, taking dictation is frustrating as you have to stop, slow down, repeat yourself, or clarify dubious words. Shorthand was one way to equip a secretary to write as fast as the boss can talk. Steno machines were another way. But the dream was always a way to just speak naturally, at your convenience, and somehow have it show up on a typewritten page. That’s where the Dictaphone company started.

History of the Dictaphone

Unsurprisingly, Dictaphone’s founder was the famous Alexander Graham Bell. Although Edison invented the phonograph, Bell made many early improvements to the machine, including the use of wax instead of foil as a recording medium. He actually started the Volta Graphophone Company, which merged with the American Graphophone Company that would eventually become Columbia Records.

In 1907, the Columbia Phonograph Company trademarked the term Dictaphone. While drum-based machines were out of style in other realms, having been replaced by platters, the company wanted to sell drum-based machines that let executives record audio that would be played back by typists. By 1923, the company spun off on its own.

Edison, of course, also created dictation machines. There were many other companies that made some kind of dictation machine, but Dictaphone became the standard term for any such device, sort of like Xerox became a familiar term for any copier.

Dictaphones were an everyday item in early twentieth-century offices for dictation, phone recording, and other audio applications. Not to mention a few other novel uses. In 1932, a vigilante organization used a Dictaphone to bug a lawyer’s office suspected of being part of a kidnapping.

Some machines could record and playback. Others, usually reserved for typists, were playback-only. In addition, some machines could “shave” wax cylinders to erase a cylinder for future use. Of course, eventually you’d shave it down to the core, and then it was done.

The Computer History Archives has some period commercials and films from Dictaphone, and you can see them in the videos below.

As mentioned, Dictaphone wasn’t the only game in town. Edison was an obvious early competitor. We were amused that the Edison devices had a switch that allowed them to operate on AC or DC current.

Later, other companies like IBM would join in. Some, like the Gray Audograph and the SoundScriber used record-like disks instead of belts or drums. Of course, eventually, magnetic tape cassettes were feasible, too, and many people made recorders that could be used for dictation and many other recording duties.

The Dictabelt

For the first half of the twentieth century, Dictaphones used wax cylinders. However, in 1947, they began making machines that pressed a groove into a Lexan belt — a “Dictabelt,” at first called a “Memobelt.” These were semi-permanent and, since you couldn’t easily melt over some of the wax, difficult to tamper with, which helped make them admissible in court. Apparently, you could play a Dictabelt back about 20 times before it would be too beat up to play.

These belts found many uses. For one, Dictaphone was a major provider to police departments and other similar services, recording radio traffic and telephone calls. In the late 1970s, the House Select Committee on Assassinations used Dictaphone belts from the Dallas police department recording in 1963 to do audio analysis on the Kennedy assassination. Many Dictaphones found homes in courtrooms, too.

As you can see in the commercials in the video, Dictabelts would fit in an envelope: they are about 3.5 in x  12 in or 89 mm x 300 mm. The “portable” machine promised to let you dictate from anywhere, keep meeting minutes, and more. A single belt held 15 minutes of audio, and the color gives you an idea of when the belt was made.

Magnetic Personality

Of course, Dictaphone wasn’t the only game in town for machines like this. IBM released one that used a magnetic belt called a “Magnabelt’ that you could edit. Dictaphone followed suit. These, of course, were erasable.

Even as late as 1977, you could find Dictaphones in “word processing operations” like the one in the video with the catchy tune, below. Of course, computers butted into both word processing and dictation with products like Via Voice or DragonDictate. Oddly, DragonDictate is from Nuance, which bought what was left of Dictaphone.

Insides

Since this is Hackaday, of course, you want to see the insides of some of these machines. A video from [databits] gives us a peek below.

Offices have certainly changed. Most people do their own typing now. Your phone can record many hours of crystal-clear audio. Computers can even take your dictation now, if you insist.

Should you ever find a Dictabelt and want to digitize it for posterity, you might find the video below from [archeophone] useful. They make a modern playback unit for old cylinders and belts.

We’d love to see a homebrew Dictabelt recorder player using more modern tech. If you make one, be sure to let us know. People recorded on the darndest things. Tape caught on primarily because of World War II Germany and Bing Crosby.

[Alexwlchan] noticed something funny. He knew that not putting a size for a video embedded in a web page would cause his page to jump around after the video loaded. So he put the right numbers in. But with some videos, the page would still refresh its layout. He learned that not all video sizes are equal and not all pixels are square.

For a variety of reasons, some videos have pixels that are rectangular, and it is up to your software to take this into account. For example, when he put one of the suspect videos into QuickTime Player, it showed the resolution was 1920×1080 (1350×1080). That’s the non-square pixel.

So just pulling the size out of a video isn’t always sufficient to get a real idea of how it looks. [Alex] shows his old Python code that returns the incorrect number and how he managed to make it right. The mediainfo library seems promising, but suffers from some rounding issues. Instead, he calls out to ffprobe, an external program that ships with ffmpeg. So even if you don’t use Python, you can do the same trick, or you could go read the ffprobe source code.

[Alex] admits that there are not many videos that have rectangular pixels, but they do show up.

If you like playing with ffmpeg and videos, try this in your browser. Think rectangular pixels are radical? There has been work for variable-shaped pixels.

Plotters aren’t as common as they once were. Today, many printers can get high enough resolution with dots that drawing things with a pen isn’t as necessary as it once was. But certainly you’ve at least seen or heard of machines that would draw graphics using a pen. Most of them were conceptually like a 3D printer with a pen instead of a hotend and no real Z-axis. But as [biosrhythm] reminds us, some plotters were suspiciously like typewriters fitted with pens.

Instead of type bars, type balls, or daisy wheels, machines like the Panasonic Penwriter used a pen to draw your text on the page, as you can see in the video below. Some models had direct computer control via a serial port, if you wanted to plot using software. At least one model included a white pen so you could cover up any mistakes.

If you didn’t have a computer, the machine had its own way to input data for graphs. How did that work? Read for yourself.

Panasonic wasn’t the only game in town, either. Silver Reed — a familiar name in old printers — had a similar model that could connect via a parallel port. Other familiar names are Smith Corona, Brother, Sharp, and Sears.

Since all the machines take the same pens, they probably have very similar insides. According to the post, Alps was the actual manufacturer of the internal plotting mechanism, at least.

The video doesn’t show it, but the machines would draw little letters just as well as graphics. Maybe better since you could change font sizes and shapes without switching a ball. They could even “type” vertically or at an angle, at least with external software.

Since plotters are, at heart, close to 3D printers, it is pretty easy to build one these days. If plotting from keystrokes is too mundane for you, try voice control.

[Engineezy] might have been watching a 3D printer move when inspiration struck: Why not build a robot arm to clean up his workbench? Why not, indeed? Well, all you need is a 17-foot-long X-axis and a gripper mechanism that can pick up any strange thing that happens to be on the bench.

Like any good project, he did it step by step. Mounting a 17-foot linear rail on an accurately machined backplate required professional CNC assistance. He was shooting for a 1mm accuracy, but decided to settle for 10mm.

With the long axis done, the rest seemed anticlimactic, at least for moving it around. The system can actually support his bodyweight while moving. The next step was to control the arm manually and use a gripper to open a parts bin.

The arm works, but is somewhat slow and needs some automation. A great start to a project that might not be practical, but is still a fun build and might inspire you to do something equally large.

We have large workbenches, but we tend to use tiny ones more often in our office. We also enjoy ones that are portable.

Color 3D printing has gone mainstream, and we expect more than one hacker will be unpacking one over the holidays. If you have, say, a color inkjet printer, the process is simple: print. Sure, maybe make sure you tick the “color” box, but that’s about it. However, 3D printers are a bit more complicated.

There are two basic phases to printing color 3D prints. First, you have to find or make a model that has different colors. Even if you don’t make your own models (although you should), you can still color prints in your slicer.

The second task is to set the printer up to deal with those multiple colors. There are several different ways to do this, and each one has its pros and cons. Of course, some of this depends on your slicer, and some depends on your printer. For the purposes of this post, I’ll assume you are using a Slic3r fork like Prusa or OrcaSlicer. Most of the lower-priced printers these days work in roughly the same way.

Current State of Color

In theory, there are plenty of ways to 3D print in color. You can mix hot plastic in the nozzle or use multiple nozzles, each loaded with a different color. But most entry-level color printers use a variation of the same technique. Essentially, they are just like single-nozzle FDM printers, but they have three extra pieces. First, there is a sensor that can tell if filament is in the hot end or not. There’s also a blade above the hot end but below the extruder that can cut the filament off cleanly on command. This usually involves having the hot end ram some actuator that pushes the spring-loaded knife through the filament.

The third piece is some unit to manage moving a bunch of filaments in and out of the hot end. Everyone calls this something else. Bambu calls it an AMS while Flashforge calls it an IFS. Prusa has an MMU. Whatever you call it, it just moves cold filament around: either pushing it into the extruder or pulling it out.

Every filament change starts with cutting the filament below the extruder. That leaves the stringy melted part down in the nozzle. Then the extruder can pull the rest up until the management unit can take over and pull it totally out of the hot end/extruder assembly. That’s why there’s a sensor. It pulls until it sees that the extruder is empty or it times out and throws an error.

Then it is simple enough to move another filament back into the extruder. Of course, the first thing it has to do is push the leftover filament out of the nozzle. Most printers move to a bin and extrude until they are sure the color has changed. However,  there are other options.

Even if you push out all the old filament, you may want to print a little waste piece of the new filament before you start printing, and this is called a purge block. Slicers can also push purge material into places like your infill, for example. Some can even print objects with the purge, presumably an object that doesn’t have to look very nice. Depending on your slicer, printer, and workflow, you can opt to print without a purge block, which can work well when you have a part where each layer is a solid color. Some printers will let you skip the discharge step, too, which is often called “poop.”

One caveat, of course, is that all this switching logic takes time and generates waste. A good rule of thumb is to try to print many objects at one time if you are going to switch filament, because the changes are what take time and generate waste. Printing dozens of objects will generate essentially the same amount of waste as printing one. Of course, printing a dozen objects will take longer than a single one, but the biggest part of the time is filament changes, which doesn’t change no matter how many or few you print.

Get Ready to Print

We’ve talked before about creating your own color objects. We’ve even seen how to do it in TinkerCad. Of course, you can also load designs that already have color in them. However, there are several different ways to put color into an otherwise monochrome print.

First, you can take a regular print and use your slicer’s paint function to paint areas with different colors. That works, but it is often tedious, and for complex shapes, it is error-prone. Another downside is that you can’t really control the depth easily, so you get strange filament shifts inside the object if you do it that way.

In Orca, you can select an object in the Prepare screen and then use N, or the toolbar, to bring up the paint color dialog. From there, you can pick a brush shape, pen size, and color. Then it is easy to just paint where you like by left-dragging. You can remove paint by pressing Shift while clicking or dragging. Press the little question mark at the bottom left to see other options.

Once you make a color print, the slicer will automatically place a purge block for you unless you turn it off. Assuming you use it, it is a good idea to drag it on the build plate to be closer to the print, which can shave a few minutes of travel time.

From Many, One

Possibly the easiest way, other than not printing in color, of course, is to have each part of the model that needs to be one color as a separate STL file, as we talked about in the previous post. You tell the slicer which part goes with which filament, and you are done.

In Orca, the best way to do this is to import several STL models at one time. The software will ask you: “Load these files as a single object with multiple parts?” If you agree, you get one object made of individual pieces.

The resulting object won’t look much different until you go to “Process”, on the left-hand side of the screen, and switch from the default Global to Objects. From there, you’ll see the objects and their components. At first, each one will be set to the same color, but by clicking on the color box, you can assign different colors. In the screenshot, you’ll see two identical objects, each with two parts. Each part has a different color. The number is the extruder that holds that color.

There is another way, though. You can avoid almost all of the waste generation and extra time if your model is designed so that each layer is a single color. People have done this for years, where you put a pause in your G-code and then switch filament manually. The idea is the same but the printer can switch for you. For example, the Christmas Tree ornament uses two filament changes to print white, then green, then white again. This works great for lettering and logos and other simple setups where you simply need some contrast.

In Orca, you’ll want to slice your model once and switch to the preview tab. Using the vertical slider on the right-hand side, adjust the view until it shows you where you want the filament change. Then right-click and select “Change Filament.” This is the same way you add a pause if you want to change filament manually, for example.

If you use this method, remember to turn off the purge block. You don’t really need it.

Summary

So now, when you unwrap that shiny new multimaterial printer, you have a plan. Get a color model or color one yourself. Then you can decide if you need color changes or full-blown, and waste-prone, color printing. Either way, have fun!

Learning something on YouTube seems kind of modern. But if you are watching a 1957 instructional film about slide rules, it also seems old-fashioned. But Encyclopædia Britannica has a complete 30-minute training film, which, what it lacks in glitz, it makes up for in mathematical rigor.

We appreciated that it started out talking about numbers and significant figures instead of jumping right into the slide rule. One thing about the slide rule is that you have to sort of understand roughly what the answer is. So, on a rule, 2×3, 20×30, 20×3, and 0.2×300 are all the same operation.

You don’t actually get to the slide rule part for about seven minutes, but it is a good idea to watch the introductory part. The lecturer, [Dr. Havery E. White] shows a fifty-cent plastic rule and some larger ones, including a classroom demonstration model. We were a bit surprised that the prestigious Britannica wouldn’t have a bit better production values, but it is clear. Perhaps we are just spoiled by modern productions.

We love our slide rules. Maybe we are ready for the collapse of civilization and the need for advanced math with no computers. If you prefer reading something more modern, try this post. Our favorites, though, are the cylindrical ones that work the same, but have more digits.

We love and hate OpenSCAD. As programmers, we like describing objects we want to 3D print or otherwise model. As programmers, we hate all the strange things about OpenSCAD that make it not like a normal programming language. Maybe µCAD (or Microcad) is the answer. This new entry in the field lets you build things programmatically and is written in Rust.

In fact, the only way to get it right now is to build it from source using cargo. Assuming you already have Rust, that’s not hard. Simply enter: cargo install microcad. If you don’t already have Rust, well, then that’s a problem. However, we did try to build it, and despite having the native library libmanifold available, Rust couldn’t find it. You might have better luck.

You can get a feel for the language by going through one of the tutorials, like the one for building a LEGO-like shape. Here’s a bit of code from that tutorial:

use std::geo2d::*;
use std::ops::*;

const SPACING = 8mm;

op grid(columns: Integer, rows: Integer) {
@input
.translate(x = [1..columns] * SPACING, y = [1..rows] * SPACING)
.align()
}

sketch Base(
columns: Integer,
rows: Integer,
width: Length,
height: Length
) {
thickness = 1.2mm;
frame = Frame(width, height, thickness);
struts = Ring(outer_d = 6.51mm, inner_d = 4.8mm)
.grid(columns = columns-1, rows = rows-1);
frame | struts;
}

There are proper functions, support for 2D sketches and 3D objects, and even a VSCode extension.

Will you try it? If we can get it to build, we will. Meanwhile, there’s always OpenSCAD. Even TinkerCAD can do some parametric modeling.

We can’t get enough of [Bettina Neumryn’s] videos. If you haven’t seen her, she takes old electronics magazines, finds interesting projects, and builds them. If you remember these old projects, it is nostalgic, and if you don’t remember them, you can learn a lot about basic electronics and construction techniques. This installment (see below) is an Elektor digital voltmeter and frequency counter from late 1981.

As was common in those days, you could find the PCB layouts in the magazine. In this case, there were two boards. The schematic shows that a counter and display driver chip — a 74C928 — does most of the heavy lifting for the display and the counter.

It is easy to understand how the frequency counter works. You clip the input with a pair of diodes, amplify it a bit, square it with a Schmitt trigger, and then, possibly, prescale it using a divider. The voltmeter is a little trickier: it uses a voltage divider, an op amp, and a 555 to convert the voltage to a frequency.

Of course, finding the parts for an old project can be a challenge. A well-stocked junk drawer doesn’t hurt. A PCB etching setup helps, too.

We’ve looked at her magazine rebuilds before. If you ever get the urge to tackle a project like this, you can find all the grand old magazines online.

If you are a schoolkid of the right age, you can’t wait to lose a baby tooth. In many cultures, there is a ritual surrounding it, like the tooth fairy, a mouse who trades your tooth for a gift, or burying the tooth somewhere significant. But in 1958, a husband and wife team of physicians wanted children’s teeth for a far different purpose: quantifying the effects of nuclear weapons testing on the human body.

Louise and Eric Reiss, along with some other scientists, worked with Saint Louis University and the Washington School of Dental Medicine to collect and study children’s discarded teeth. They were looking for strontium-90, a nasty byproduct of above-ground nuclear testing. Strontium is similar enough to calcium that consuming it in water and dairy products will leave the material in your bones, including your teeth.

The study took place in the St. Louis area, and the results helped convince John F. Kennedy to sign the Partial Nuclear Test Ban Treaty.

They hoped to gather 50,000 teeth in a year. By 1970, 12 years later, they had picked up over 320,000 donated teeth. While a few kids might have been driven by scientific altruism, it didn’t hurt that the program used colorful posters and promised each child a button to mark their participation.

Children’s teeth were particularly advantageous to use because they are growing and are known to readily absorb radioactive material, which can cause bone tumors.

Scale

You might wonder just how much nuclear material is floating around due to bombs. Obviously, there were two bombs set off during the war, as well as the test bombs required to get to that point. Between 1945 and 1980, there were five countries conducting atmospheric tests at thirteen sites. The US, accounting for about 65% of the tests, the USSR, the UK, France, and China detonated 504 nuclear devices equivalent to about 440 megatons of TNT.

Well over 500 bombs with incredible force have put a lot of radioactive material into the atmosphere. That doesn’t count, too, the underground tests that were not always completely contained. For example, there were two detonations in Mississippi where the radiation was contained until they drilled holes for instruments, leaving contaminated soil on the surface. Today, sites like this have “monuments” explaining that you shouldn’t dig in the area.

Of course, above-ground tests are worse, with fallout affecting “downwinders” or people who live downwind of the test site. There have been more than one case of people, unaware of the test, thinking the fallout particles were “hot snow” and playing in it. Test explosions have sent radioactive material into the stratosphere. This isn’t just a problem for people living near the test sites.

Results

By 1961, the team published results showing that strontium-90 levels in the teeth increased depending on when the child was born. Children born in 1963 had levels of strontium-90 fifty times higher than those born in 1950, when there was very little nuclear testing.

The results were part of the reason that President Kennedy agreed to an international partial test ban, as you can see in the Lincoln Presidential Foundation video below. You may find it amazing that people would plan trips to watch tests, and they were even televised.

In 2001, Washington University found 85,000 of the teeth stored away. This allowed the Radiation and Public Health Project to track 3,000 children who were, by now, adults, of course.

Sadly, 12 children who had died from cancer before age 50 had baby teeth with twice the levels of the teeth of people who were still alive at age 50. To be fair, the Nuclear Regulatory Commission has questioned these findings, saying the study is flawed and fails to account for other risk factors.

And teeth don’t just store strontium. In the 1970s, other researchers used baby teeth to track lead ingestion levels. Baby teeth have also played a role in the Flint Water scandal. In South Africa, the Tooth Fairy Project monitored heavy metal pollution in children’s teeth, too.

Teeth aren’t the only indicator of nuclear contamination. Steel is also at risk.

Featured image: “Castle Bravo Blast” by United States Department of Energy.

[Big Clive] picked up a tiny heater for less than £8 from the usual sources. Would you be shocked to learn that its heating capacity wasn’t as advertised? No, we weren’t either. But [Clive] treats us to his usual fun teardown and analysis in the video below.

A simple test shows that the heater drew about 800 W for a moment and drops as it heats until it stabilizes at about 300 W. Despite that, these units are often touted as 800 W heaters with claims of heating up an entire house in minutes. Inside are a fan, a ceramic heater, and two PCBs.

The ceramic heaters are dwarfed by metal fins used as a heat exchanger. The display uses a clever series of touch sensors to save money on switches. The other board is what actually does the work.

[Clive] was, overall, impressed with the PCB. A triac runs the heaters and the fan. It also includes a thermistor for reading the temperature.

You can learn more about the power supply and how the heater measures up in the video. Suffice it to say, that a cheap heater acts like a cheap heater, although as cheap heaters go, this one is built well enough.

We were as excited as anyone when MARSIS (the Mars Advanced Radar for Subsurface and Ionosphere Sounding) experiment announced there was possibly liquid water under the southern polar ice cap. If there is liquid water on Mars, it would make future exploration and colonization much more feasible. Unfortunately, SHARAD (the Shallow Radar) has a new trick that suggests the data may not indicate liquid water after all.

While the news is a bummer, the way scientists used SHARAD to confirm — or, in this case, deny — the water hypothesis was a worthy hack. The SHARAD antenna is on the Mars Reconnaissance Orbiter, but in a position that makes it difficult to obtain direct surface readings from Mars. To compensate, operators typically roll the spacecraft to give the omnidirectional antenna a clearer view of the ground. However, those rolls have been under 30 degrees.

Computer modelling indicated that rolls of 120 degrees would greatly improve the SHARAD data. So far, four of these “very large roll” or VLR maneuvers have allowed more detailed probes of the surface with SHARAD. Unfortunately the new data didn’t back up the early findings. Scientists now think the reflection may be just an unusually flat surface under the ice.

Of course, just because there might not be water in that location doesn’t mean there isn’t any at all. Want to live on Mars? There’s a lot to think about.

When you think of ultrasonics,  you probably think of a cleaner or maybe a toothbrush. If you are a Star Trek fan, maybe you think of knocking out crew members or showers. But there is another practical use of ultrasonics: cutting. By vibrating a blade at 40 kHz or so, you can get clean, precise cuts in a variety of materials. The problem? Commercial units are quite expensive. So [Electronoobs] decided to roll his own. Check it out in the video below.

There are dreams and then there’s reality. Originally, the plan was for a handheld unit, but this turned out not to be very practical. Coil actuators were too slow. Piezo elements made more sense, but to move the blade significantly, you need a larger element.

Taking apart an ultrasonic cleaner revealed a very large element, but mounting it to a small blade would be a problem. The next stop was an ultrasonic toothbrush. Inside was a dual piezo element with an interesting trick. The elements were mounted in a horn that acts like an ultrasonic megaphone, if you will.

These horns are available, and he found an off-the-shelf solution with four piezos and a large horn that seemed promising. Driving the elements, though, requires a 40 kHz 100 VAC signal. His original board didn’t work — but he’s not giving up. But, for now, he used a simple circuit on a breadboard. However, it didn’t make a strong vibration, even with a larger horn.

Comparison with ultrasonic cleaners showed that his output voltage wasn’t enough. The expedient answer was to buy an ultrasonic cleaner kit (who knew they came as kits?) and use the boards from it to drive the horn and the blade. That worked very well.

His current thinking is that the cleaner driver may be too large, since the blade and horn get hot in use. But he still encased it with a 3D printed case and wound up with a usable tool. His next version should be portable and maybe run a little cooler.

Ultrasonic sensors are, of course, super useful. Or you can always levitate tiny things with it.

We aren’t sure why, but [Lev Chizhov] and some other researchers have found a way to make you smell things by hitting your head with ultrasound. Apparently, your sense of smell lives in your olfactory bulb, and no one, until now, has thought to try zapping it with ultrasound to see what happens.

The bulb is somewhere behind your nose, as you might expect. This is sub-optimal for ultrasound because your nose isn’t flat, and it is full of air. Packing a subject’s nose with gel wasn’t going to win many fans. The answer was to place the transducer on the person’s forehead and shoot down at the bulb. They made a custom headset that let them precisely target areas of the subject’s bulb guided by an MRI.

So far, they have a sample size of two, but they’ve managed to induce the smell of fresh air, garbage, ozone, and burning wood. What would you do with this? Smell-o-vision? A garbage truck VR game? Let us know in the comments. We don’t think this is exactly how the last VR smell gadget we saw worked, but — honestly — we aren’t completely sure.

The BBC wanted to show everyone how a computer might be used in schools. A program aired in 1979 asks, “Will Computers Revolutionise Education?” There’s vintage hardware and an appearance of PILOT, made for computer instructions.

Using PILOT looks suspiciously like working with a modern chatbot without as much AI noise. The French teacher in the video likes that schoolboys were practicing their French verb conjugation on the computer instead of playing football.

If you want a better look at hardware, around the five-minute mark, you see schoolkids making printed circuit boards, and some truly vintage oscilloscope close-ups. There are plenty of tiny monitors and large, noisy printing terminals.

You have to wonder where the eight-year-olds who learned about computers in the video are today, and what kind of computer they have. They learned binary and the Towers of Hanoi. Their teacher said the kids now knew more about computers than their parents did.

As a future prediction, [James Bellini] did pretty well. Like many forecasters, he almost didn’t go far enough, as we look back almost 50 years. Sure, Prestel didn’t work out as well as they thought, dying in 1994. But he shouldn’t feel bad. Predicting the future is tough. Unless, of course,  you are [Arthur C. Clarke].

We think of radios as audio devices, but for people who are visually impaired, it can be difficult to tell which channel you are listening to at any given time. [Sncarter] has a family member with vision impairment and built a radio to help her. Unfortunately, it was difficult to replicate, so he decided to try again. The result is an FM radio that provides audible status notifications about power and frequency. Check it out in the video below.

This isn’t just some hacked-up commercial radio, but a ground-up design that uses a TEA5767 with an ATMega328 for control. There is an LCD for when someone else might use the radio and an audio amplifier. He built the prototype on a breadboard, but moved the finished product to a PCB.

It isn’t just the electronics and the sound that are assistive. The case has raised bosses to help the user find things like the switch and rotary encoder. The Arduino can speak frequency announcements, although the quality of the voice is something he wants to tackle in the next revision.

These radios on a chip give you many design options. These same ideas can be useful for audiobook players, too.

You have that slide rule in the back of the closet. Maybe it was from your college days. Maybe it was your Dad’s. Honestly. Do you know how to use it? Really? All the scales? That’s what we thought. [Amen Zwa, Esq.] not only tells you how slide rules came about, but also how to use many of the common scales. You can also see his collection and notes on being a casual slide rule collector and even a few maintenance tips.

The idea behind these computing devices is devilishly simple. It is well known that you can reduce a multiplication operation to addition if you have a table of logarithms. You simply take the log of both operands and add them. Then you do a reverse lookup in the table to get the answer.

For a simple example, you know the (base 10) log of 10 is 1 and the log of 1000 is 3. Adding those gives you 4, and, what do you know, 10⁴ is 10,000, the correct answer. That’s easy when you are working with numbers like 10 and 1000 with base 10 logarithms, but it works with any base and with any wacky numbers you want to multiply.

The slide rule is essentially a log table on a stick. That’s how the most common scales work, at least. Many rules have other scales, so you can quickly, say, square or cube numbers (or find roots). Some specialized rules have scales for things like computing power.

We collect slide rules, too. Even oddball ones. We’ve often said that the barrier of learning to use a slide rule weeded out many bad engineers early.

Since the dawn of computers, we’ve tried different ways to store data. These days, you grab data over the network, but you probably remember using optical disks, floppies, or, more recently, flash drives to load something into your computer. Old computers had to use a variety of methods, such as magnetic tape. But many early computers used some technology that existed from the pre-computer era, like punched cards or, as [Anthony Francis-Jones] shows us, paper tape.

Paper tape was common in TeleType machines and some industrial applications. In fact, as early as 1725, looms could use paper tape, which would eventually lead to punched cards. For computers, there were two common variations that differed in how many holes were punched across the tape: 5 or 8. There was also a small sprocket hole that allowed a gear to move the tape forward through a reader.

Typically, brushes or optical sensors would read the holes into the computer. Some paper tape used regular paper, but others used oily paper. You could also get tapes made out of mylar, which was very durable.

The other big difference in tapes was in how they were punched. A conventional tape had the entire hole punched out, leaving confetti-like “chad.” There were also chadless tapes where the chad was left slightly connected to the paper.

One common feature of paper tape was that it would skip any section where every hole had been punched. This allowed you to erase parts of the tape by punching over it. Then, with scissors and tape, you could splice sections by lining up the fully punched areas between two sections of tape. You could also make endless loops of tape.

Paper tape was used as a crude word processor back in the day. They were even used to send wire photos.

If you’ve ever used an NE602 or similar IC to build a radio, you might have noticed that the datasheet has a “gilbert cell” mixer. What is that? [Electronics for the Inquisitive Experimenter] explains them in a recent video. The gilbert cell is a multiplier, and multiplying two waveforms will work to mix them together.

At the heart of the gilbert cell is essentially three differential amplifiers that share a common current source. The video shows LTSpice simulations of the circuits as he explains them.

One reason these work well on ICs is that they require very closely-matched transistors. In real life, it is hard to get transistors that match exactly. But when they are all on the same slab of silicon, it is fairly straightforward.

What we really like is that after simulating and explaining the circuit, he explains why multipliers mix signals, then builds a real circuit on the bench using discrete transistors and matched transistor arrays. There is a bit of trigonometry in the explanation, but nothing too difficult.

Of course, the most common application of differential amplifiers is the op amp. The NE602 is out of production, sadly, but if you can find any, they make dandy receivers.

[Zack], in addition to being a snappy dresser, has a thing for strange 3D printing filament. How strange? Well, in a recent video, he looks at filaments that require 445 C. Even the build plate has to be super hot. He also looks at filament that seems like iron, one that makes you think it is rubber, and a bunch of others.

As you might expect, he’s not using a conventional 3D printer. Although you might be able to get your more conventional printer to handle some of these, especially with some hacking. There is filament with carbon fiber, glass fiber, and more exotic add-ons.

Most of the filaments need special code to get everything working. While you might think you can’t print these engineering filaments, it stands to reason that hobby-grade printers are going to get better over time (as they already have). If the day is coming when folks will be able to print any of these on their out-of-the-box printer, we might as well start researching them now.

If you fancy a drinking game, have a shot every time he changes shots and a double when the Hackaday Prize T-shirt shows up.

You might be surprised to find out that [Akshat Joshi’s] Pong game that fits in a 512-byte boot sector isn’t the first of its kind. But that doesn’t mean it isn’t an accomplishment to shoehorn useful code in that little bitty space.

As you might expect, a game like this uses assembly language. It also can’t use any libraries or operating system functions because there aren’t any at that particular time of the computer startup sequence. Once you remember that the bootloader has to end with two magic bytes (0x55 0xAA), you know you have to get it all done in 510 bytes or less.

This version of Pong uses 80×25 text mode and writes straight into video memory. You can find the code in a single file on GitHub. In the old days, getting something like this working was painful because you had little choice but reboot your computer to test it and hope it went well. Now you can run it in a virtual machine like QEMU and even use that to debug problems in ways that would have made a developer from the 1990s offer up their life savings.

We’ve seen this before, but we still appreciate the challenge. We wonder if you could write Pong in BootBasic?