Reconstructing Data From A Corrupt Apple ][ Floppy Disk

January 27, 2021 by 47 Comments

Back in 1990 [Benjamin Zotto] wrote – while in elementary school – a dog racing game called Wonderland 2. The BASIC source code and images for the game were stored on a single ProDOS formatted, soft-sectored 5.25″ floppy disk. Fast-forward thirty years to today and [Benjamin] found to his dismay that ProDOS could no longer read the floppy, giving an I/O error. Not deterred, he set about to recover the data, as documented in this Twitter thread.

Applesauce visualization of the patterns on the corrupted disk, with soft-sectoring spiral arms.

The gist of the story is that the floppy disk’s surface could still be scanned with help from the aptly named Applesauce Floppy Drive Controller, which got the following visualization of the magnetic patterns on the disk surface:

This data could then be analyzed sector by sector, with the bad sectors and the cause for ProDOS flaking out with its reading attempts here marked in red.

Checking the data recovered so far confirmed that it was a ProDOS disk. It also confirmed that the sector containing the directory listing was shot. This required diving into the technical reference manual for ProDOS and its filesystem to figure out how to reconstruct the directory layout. This required figuring out the offsets and sizes of the files, assisted by knowing what was likely on the disk, and having some bits and pieces of the original volume listing still intact. This allowed for the directory volume to be rebuilt, one byte at a time.

Sectors on the disk, with bad sectors in red.

At the end of that arduous and highly educational journey success waited, and [Benjamin] was once again able to relive his memories of 1990s BASIC and hand-drawn bitmap graphics.

Arduino Learns The Martial Arts With Nunchucks Input Device

January 26, 2021 by 11 Comments

There is a boring part of every computer introduction class that shows how a computer is made up of input, output, and processing. Maybe it wouldn’t be so boring if the input device was a nunchuck. [Brian Lough] thinks so and he belligerently asserts that nunchucks are the best input device ever. With a simple connection to a Wii controller and an associated library, you get access to an analog joystick, two buttons, and an accelerometer.

The nunchuck is meant to plug into a Wii controller and the connection is I2C, so that’s trivial to interface to an Arduino or other small microcontroller. The only issue is making the connection. We might have just snipped the wires, but [Brian] prefers to use a small breakout board that plugs into the stock connector and provides solder points for your own cable. There are options for the breakout boards, and [Brian] has his own design that you can get from OSHPark for about a buck for three boards. You can also just jam wire into the connector, but that’s not always robust.

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How To Keep Your Head Warm With A Skirt

January 26, 2021 by 58 Comments

We’re not sure what we like better about this upcycled trapper hat — that [ellygibson] made it as a tribute to Holden Caulfield, the anti-hero of the classic teen angst novel The Catcher in the Rye, or the fact that she made it out of a skirt that cost a dollar from the thrift store. Oddly enough, one dollar is exactly what Holden paid for his hat in the book.

To make this hat, [elly] started by measuring the circumference of her head, then used math to figure out the radius of the circle for the top part. She made a prototype first to get the fit right, then cut the pieces from the skirt and the lining pieces from black flannel. We love that [elly] used the tiny pocket from the skirt in one of the ear flaps, because it will surely come in handy one day.

[elly] doesn’t provide pattern pieces, but that’s okay — between the explanation of how she arrived at the hat band circumference and the step-by-step instructions, it should be easy to make one of these for yourself from whatever fabric you’ve got.

Before you go cutting up an old coat, consider whether it could be fixed. Remember when [Ted Yapo] fixed the zipper box on his son’s winter coat by printing a replacement? Or how about the time [Gerrit Coetzee] cast his own pea coat buttons?

Dreaming Of A Transparent (PCB) Christmas

January 26, 2021 by 1 Comment

[Carl] wanted to put his force sensors on a transparent PCB and had to ask his board vendor for a special sample. Flexible PCBs are available on transparent substrates made of PET, but they are not as common as polyimide boards. As [Carl] found out, these boards are a bit thicker, a bit less flexible, and don’t hold up to very high heat as well as the standard boards. Undeterred, he designed a 3D Christmas tree using the clear boards. The result that you can see in the video below looks pretty good and would have been hard to duplicate with conventional means.

When you build the board it is as a flat spiral, but lifting it in the center allows it to expand into a conical tree shape. The circuit itself is just an LED blinker, but the flexible board is the interesting part.

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Chasing Down Bad Caps To Save A Troubled PSU

January 26, 2021 by 36 Comments

We know what you’re thinking. It’s a bad power supply, of course it was capacitors to blame. But even if we all intuitively know at this point that bad caps are almost always the culprit when a PSU gives up the ghost, it’s not always easy to figure out which one is to blame. Which is why this deep dive into a failed ETK450AWT by [eigma] is worth a look.

The first sign of trouble was when the computer would unexpectedly reboot with nothing in the system logs to indicate a problem. Eventually, [eigma] noticed a restart before the operating system even loaded, which confirmed the hardware was to blame. A quick look at the PSU output with a voltmeter showed things weren’t too far out of spec, but putting an oscilloscope on the 12 V line uncovered a nasty waveform that demanded further investigation.

Connecting all the dots.

By carefully following traces and comparing with common PSU diagrams, [eigma] was able to identify the SG5616 IC that checks the various voltages being produced by the PSU and generates the PWR_OK signal which tells the motherboard that everything is working normally. As before, all of the DC voltages at this chip seemed reasonable enough, but the pin that was measuring AC voltage from the transformer was showing the same ripple visible on the 12 VDC line.

Even more digging uncovered that the transformer itself had a control IC nestled away. The 13 VDC required by this chip to operate is pulled off the standby transformer by way of a Zener diode and a couple capacitors, but as [eigma] soon found, the circuit was producing another nasty ripple. Throwing a few new capacitors into the mix smoothed things out and got the PSU to kick on, but that’s not quite the end of the story.

Pulling the capacitors from the board and checking their values with the meter, [eigma] found they too appeared to be within reasonable enough limits. They even looked in good shape physically. But with the help of a signal generator, he was able to determine their equivalent series resistance (ESR) was way too high. Case closed.

While swapping out blown capacitors in older electronics is something of a rite of passage for hardware hackers, this case is an excellent example of how even the simplest of fixes can be tricky to troubleshoot.

How Does A Circuit Breaker Break?

January 26, 2021 by 32 Comments

Even if you aren’t an electronics person, you probably have a working knowledge of circuit breakers. When the lights go out, you find the circuit breaker and flip it back to the on position. Most people understand, too, that the breaker will trip if you overload the circuit with too many things plugged in or with an accidental short circuit. But how does this common device actually work? Keep in mind, circuit breakers need to be super reliable and have been around long enough that you can imagine they are pretty low tech. [Learn Engineering] has a very clear video about what goes on inside a circuit breaker that’s worth the eight minutes to watch. You can see the video below.

The handle is a mechanical engineering marvel, using two springs and a special design so that even a tiny force will cause it to snap to the off position. That takes care of a human tripping it. However, you have two other cases where you want to turn it off: overload and short circuit.

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Cable Mechanism Maths: Designing Against The Capstan Equation

January 26, 2021 by 20 Comments

I fell in love with cable driven mechanisms a few years ago and put together some of my first mechanical tentacles to celebrate. But only after playing with them did I start to understand the principles that made them work. Today I want to share one of the most important equations to keep in mind when designing any device that involves cables, the capstan equation. Let some caffeine kick in and stick with me over the next few minutes to get a sense of how it works, how it affects the overall friction in your system, and how you can put it to work for you in special cases.

A Quick Refresher: Push-Pull Cable Driven Mechanisms

But first: just what exactly are cable driven mechanisms? It turns out that this term refers to a huge class of mechanisms, so we’ll limit our scope just to push-pull cable actuation systems.

These are devices where cables are used as actuators. By sending these cables through a flexible conduit, they serve a similar function to the tendons in our body that actuate our fingers. When designing these, we generally assume that the cables are both flexible and do not stretch when put in tension. Continue reading “Cable Mechanism Maths: Designing Against The Capstan Equation” →