Re-Capping An Ancient Apple PSU

April 30, 2016 by Jenny List 35 Comments

It sometimes comes as a shock when you look at a piece of hardware that you maybe bought new and still consider to be rather high-tech, and realise that it was made before someone in their mid-twenties was born. It’s the moment from that Waylon Jennings lyric, about looking in the mirror in total surprise, hair on your shoulders and age in your eyes. Yes, those people in their mid-twenties have never even heard of Waylon Jennings.

[Steve] at Big Mess o’Wires has a Mac IIsi from the early 1990s that wouldn’t power up. He’d already had the life-expired electrolytic capacitors replaced on the mainboard, so the chief suspect was the power supply. That miracle of technology was now pushing past a quarter century, and showing its age. In case anyone is tempted to say they don’t make ’em like they used to, [Steve]’s PSU should dispel the myth.

It’s easy as an electronic engineer writing this piece to think: So? Just open the lid, pop out the old ones and drop in the new, job done! But it’s also easy to forget that not everyone has the same experiences and opening up a mains PSU is something to approach with some trepidation if you’re not used to working with line power. [Steve] was new to mains PSUs and considered sending it to someone else, but decided he *should* be able to do it so set to work.

The Apple PSU is a switch-mode design. Ubiquitous today but still a higher-cost item in those days as you’ll know if you owned an earlier Commodore Amiga whose great big PSU box looked the same as but weighed ten times as much as its later siblings. In simple terms, the mains voltage is rectified to a high-voltage DC, chopped at a high frequency and sent through a small and lightweight ferrite-cored transformer to create the lower voltages. This means it has quite a few electrolytic capacitors, and some of them are significantly stressed with heat and voltage.

Forum posts on the same PSU identified three candidates for replacement – the high voltage smoothing capacitor and a couple of SMD capacitors on the PWM control board. We’d be tempted to say replace the lot while you have it open, but [Steve] set to work on these three. The smoothing cap was taken out with a vacuum desoldering gun, but he had some problems with the SMD caps. Using a hot air gun to remove them he managed to dislodge some of the other SMD components, resulting in the need for a significant cleanup and rework. We’d suggest next time forgoing the air gun and using a fine tip iron to melt each terminal in turn, the cap only has two and should be capable of being tipped up with a pair of pliers to separate each one.

So at the end of it all, he had a working Mac with a PSU that should be good for another twenty years. And he gained the confidence to recap mains power supplies.

If you are tempted to look inside a mains power supply you should not necessarily be put off by the fact it handles mains voltage as long as you treat it with respect. Don’t power it up while you have it open unless it is through an isolation transformer, and remember at all times that it can generate lethal voltages so be very careful and don’t touch it in any way while it is powered up. If in doubt, just don’t power it up at all while open. If you are concerned about high voltages remaining in capacitors when it is turned off, simply measure those voltages with your multimeter. If any remain, discharge them through a suitable resistor until you can no longer measure them. There is a lot for the curious hacker to learn within a switch mode PSU, why should the electronic engineers have all the fun!

This isn’t the first recapping story we’ve covered, and it will no doubt not be the last. Browse our recapping tag for more.

Windows 95 On An Apple Watch

April 30, 2016 by Jenny List 26 Comments

What happens if the slick user interface and tight iOS integration of your Apple Watch leave you wanting more? A real operating system, from the days when men were men and computers were big grey boxes!

[Nick Lee] solved this unexpected problem with his Watch by getting a working copy of Windows 95 to run on it. On paper it shouldn’t be at all difficult, with a 520 MHz ARM, 512 MB of RAM, and 8GB of storage you might think that it would eclipse the quick 486s and low-end Pentiums we ran ’95 on back in the day with ease. But of course, the ability to run aged Redmond operating systems on a Watch was probably not at the top of the Apple dev team’s feature list, so [Nick] had to jump through quite a few hoops to achieve it.

As you might expect, the ’95 installation isn’t running directly on the Watch. In the absence of an x86 processor his complex dev process involved getting the Bochs x86 emulator to compile for the Watch, and then giving that a ’95 image to boot. The result is comically slow, with a 1-hour boot time and a little motor attached to the Watch to vibrate it and stop it going to sleep. It’s not in any way a useful exercise, after all who’d really want to use ’95 on a Watch? Internet Explorer 3 and The Microsoft Network, how handy! But it’s one of those “because you can” exercises, and we applaud [Nick] for making it happen. If you want to give it a try, his Bochs-forWatchOS code is on Github.

The video below the break shows the process of booting the ’95 Watch, opening the Start Menu, and running one of the card games. One can almost feel the lengthening shadows outside as it goes.

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The Gerber Behind Gerber Files

April 29, 2016 by Jenny List 12 Comments

When we create a printed circuit board, the chances are these days that we’ll export it through our CAD package’s CAM tool, and send the resulting files to an inexpensive PCB fabrication house. A marvel of the modern age, bringing together computerised manufacturing, the Internet, and globalised trade to do something that would have been impossible only a few years ago without significant expenditure.

Those files we send off to China or wherever our boards are produced are called Gerber files. It’s a word that has become part of the currency of our art, “I’ll send them the Gerbers” trips off the tongue without our considering the word’s origin.

This morning we’re indebted to [drudrudru] for sending us a link to an EDN article that lifts the lid on who Gerber files are named for. [H. Joseph Gerber] was a prolific inventor whose work laid the ground for the CNC machines that provide us as hackers and makers with so many of the tools we take for granted. Just think: without his work we might not have our CNC routers, 3D printers, vinyl cutters and much more, and as for PCBs, we’d still be fiddling about with crêpe paper tape and acetate.

An Austrian Holocaust survivor who escaped to the USA in 1940, [Gerber] began his business with an elastic variable scale for performing numerical conversions that he patented while still an engineering student. The story goes that he used the elastic cord from his pyjamas to create the prototype. This was followed by an ever-more-sophisticated range of drafting, plotting, and digitizing tools, which led naturally into the then-emerging CNC field. It is probably safe to say that in the succeeding decades there has not been an area of manufacturing that has not been touched by his work.

So take a look at the article, read [Gerber]’s company history page, his Wikipedia page, raise a toast to the memory of a great engineer, and never, ever, spell “Gerber file” with a lower-case G.

The Minimin Aims To Be The Simplest Theremin

April 26, 2016 by Jenny List 5 Comments

Hackaday.io user [eagleisinsight] is a high-school hacker whose dreams of becoming a Theremin virtuoso were thwarted by the high cost of a commercial instrument. His response is the Minimin, an affordable Theremin design using a 555 and an ATMega328.

The 555 is configured as an astable oscillator running at about 5MHz and with a loop antenna attached to its timing capacitor. The parasitic capacitance of the musician’s hand against the antenna varies the frequency of the oscillation, as you would expect. In a classic Theremin the signal from the 555 would be mixed with the output from a fixed 5MHz oscillator and the sound would be generated from the difference between the two oscillators, but in [eagleisinsight]’s design the 555 clocks the ATMega328’s timer. The processor can thus read the oscillator frequency and use that value to control a waveform generator.

There is something missing from this Theremin: a second antenna for volume. For now a potentiometer does that job, but [eagleisinsight] is working on a MkII device to correct this omission, along with plans to replace the ATMega with an XMega processor whose DAC can produce a sine wave output and whose USB port can be used to enable the Minimin as a MIDI controller.

As you might expect, we’ve covered numerous Theremins over the years here on Hackaday. You can browse them all, but we’d like to draw your attention to a typical breadboard instrument using a soda can antenna, people using Theremins as Guitar Hero controllers, and Léon Theremin’s terpistone, a full-body instrument.

Pillaging The Wealth Of Information In A Datasheet

April 26, 2016 by Jenny List 33 Comments

It’s a fair assumption that the majority of Hackaday readers will be used to working with electronic components, they are the life blood of so many of the projects featured here. In a lot of cases those projects will feature very common components, those which have become commoditized through appearing across an enormous breadth of applications. We become familiar with those components through repeated use, and we build on that familiarity when we create our own circuits using them.

All manufacturers of electronic components will publish a datasheet for those components. A document containing all the pertinent information for a designer, including numerical parameters, graphs showing their characteristics, physical and thermal parameters, and some application information where needed. Back in the day they would be published as big thick books containing for example the sheets for all the components of a particular type from a manufacturer, but now they are available very conveniently online in PDF format from manufacturer or wholesaler websites.

Datasheets are a mine of information on the components they describe, but sometimes they can be rather impenetrable. There is a lot of information to be presented, indeed when the device in question is a highly integrated component such as a DSP or microprocessor the datasheet can resemble a medium-sized book. We’re sure that a lot of our readers will be completely at home in the pages of a datasheet, but equally it’s a concern that a section of the Hackaday audience will not be so familiar with them and will not receive their full benefit. Thus we’re going to examine and explain a datasheet in detail, and hopefully shed some light on what it contains.

The device whose datasheet we’ve chosen to put under the microscope is a transistor. The most basic building block of active semiconductor circuits, and the particular one we’ve chosen is a ubiquitous NPN signal transistor, the 2N3904. It’s been around for a very long time, having been introduced by Motorola in the 1960s, and has become the go-to device for a myriad circuits. You can buy 2N3904s made by a variety of manufacturers all of whom publish their own data sheets, but for the purposes of this article we’ll be using the PDF 2N3904 data sheet from ON Semiconductor, the spun-off former Motorola semiconductor division. You might find it worth your while opening this document in another window or printing it out for reference alongside the rest of this article.

Let’s take a look at all the knowledge enshrined in this datasheet, and the engineering eye you sometimes need to assign meaning to those numbers, diagrams, and formulas.

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Retrotechtacular: MONIAC

April 26, 2016 by Jenny List 26 Comments

There is an argument to be made that whichever hue of political buffoons ends up in Number 10 Downing Street, the White House, the Élysée Palace, or wherever the President, Prime Minister or despot lives in your country, eventually they will send the economy down the drain.

Fortunately, there is a machine for that. MONIAC is an analogue computer with water as its medium, designed to simulate a national economy for students. Invented in 1949 by the New Zealand economist [WIlliam Phillips], it is a large wooden board with a series of tanks interconnected by pipes and valves. Different sections of the economy are represented by the water tanks, and the pipes and valves model the flow of money between them. Spending is downhill gravitational water flow, while taxation is represented by a pump which returns money to the treasury at the top. It was designed to represent the British economy in the late 1940s as [Philips] was a student at the London School of Economics when he created it. Using the machine allowed students and economists for the first time to simulate the effects of real economic decisions in government, in real time.

So if you have a MONIAC, you can learn all about spectacularly mismanaging the economy, and then in a real sense flush the economy down the drain afterwards. The video below shows Cambridge University’s restored MONIAC in operation, and should explain the device’s workings in detail.
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Workshops For Timid Solderers

April 25, 2016 by Jenny List 35 Comments

As a hackspace member, it’s easy to fall into the belief that your own everyday skills are universal. Soldering for example. You’ve handled an iron since you were a youngster, the solder bends to your will as a matter of course, and since you see your fellow makers doing the same thing you might imagine that it’s a universal hackspace skill. Everyone can do it, can’t they?

Of course, they can’t. If you weren’t lucky enough to have a parent who tolerated your occasional propensity for acquiring burns on your fingers then you probably won’t have that innate experience with an iron. This extends to people you might expect to have those skills, indeed as an electronic engineering student a couple of decades ago your scribe was surprised to find that the ability to solder was her hotly tradeable skill, amazingly even a lot of EE students couldn’t solder.

So the ability to solder is not as universal as we might expect, and your hackspace will attract plenty of people for whom it is an as-yet-unknown art. What do you do about it? If you are Vancouver Hackspace, you run a workshop whose participants are introduced to soldering through building a simple AM radio. The kit itself is not too special, it looks like one of the Elenco educational kits, but it is what the workshop represents that is important. A hackspace lives or dies by how it shares its skills, and Vancouver’s workshop is a fantastic piece of community engagement. We’d like to see more spaces doing this kind of thing.

So, perhaps it’s time to put our money where our mouth is. How difficult would it be to run a hackspace soldering workshop for the uninitiated? Assuming your space is used to the mechanics of running events, the challenge is to find for each participant a soldering iron, some solder, and a radio or other kit without breaking the bank. An ideal budget from where this is being written in the UK would be £20 (about $29), into which a Chinese kit from AliBaba or similar and a cheap iron kit could be fitted. Some work to decipher the Chinese instructions with the help of an overseas student member and to write an English manual, and we’d be ready to go. If this comes together we’ll report back on whether the non-solderers of our hackspace successfully learned the craft.

We recently featured a similar educational initiative, a course at Swansea Hackspace teaching robotics through an Arduino robot. We would like to encourage this kind of thing, what is your hackspace doing in this line?