Новини світу мікро- та наноелектроніки

Back in the early ‘90s, at the television station where I worked, we had a newsroom computer system that the reporters, anchors, and producers used to write and produce the newscasts. The system employed a pair of redundant servers and a newsroom full of PC workstations. The servers ran IBM’s OS/2 operating system, using the latest 90 MHz Pentium processors. (Ooh, that was fast!)

The workstations used 33 MHz 80386 CPUs running MS-DOS. No hard drives – just 3½” floppy disks. The floppy disks booted the computers to MS-DOS, and then ran a batch file that loaded the newsroom system’s executable program from the server. All the data, such as news stories and newscast rundowns, were stored on the server and everything connected over 10Base-T Ethernet running on a network hub (this was prior to network switches).

It all worked very well … that is, until one of our 11pm news anchors began reporting a problem.

Her workstation was occasionally and spontaneously rebooting, causing her to lose her unsaved work. We couldn’t find anything wrong with the workstation, so we replaced it. No good. We replaced her keyboard. Still no good. (No mouse change – there was no mouse; this was character mode MS-DOS.)

We replaced her network cable, changed to a different hub port, changed to a different homerun cable, and we even changed her monitor. Some of the swaps we did twice, but it still happened!

Finally, one day she wrote a very polite email to the news director, complaining that she had lost an hour’s work the previous night because her machine had rebooted, and she had to stay well past midnight rewriting her story. “If this keeps up, I’m afraid I’m going to have to ask for a new machine.” 

The news director called me and asked what was going on. I told him she apparently didn’t realize we had already given her two new machines. It didn’t seem to be a hardware problem. We decided to send one of my engineers to sit with her to see if he could figure out what was happening. I should have done that much earlier, as it took him less than five minutes to find the culprit.

The news anchor’s CPU tower was located on the floor under her desk, sitting on a short box. Back in those days, the CPU box had two buttons on the front – a power button and a reset button. The reset button connected directly to the NMI (non-maskable interrupt) pin on the microprocessor. Pressing the reset button produced an instantaneous hard reboot of the computer. 

She liked to sit with her legs crossed while she typed. While sitting with her our engineer looked down, and said, “How often do you figure you hit the reset button with the tip of your pointed high-heel shoe?”

And that, was that. 

Robert Yankowitz has been Chief Engineer at a television station in Boston, Massachusetts since 1999. Prior to that, he worked for 15 years at a station in an undisclosed city (to protect those with high-fashion footwear from embarrassment).

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Fuses are an essential part of many system designs, and we’ve come to depend on them since the earliest days of electricity. The basic concept of using a fusible link—which self-heats due to current flow and then opens to cut off current flow if there is an overcurrent condition—is simple, reliable, clear cut, and unambiguous. Fuse protects subcircuits against localized faults in a device like power regulator and implements system and user protection as mandated by regulatory standards.

Among the most widely used fuse body sizes is the 3AG size—measuring 6.3 mm x 32 mm—which is available in standard ratings from 100 mA to 15 A, in fast-acting, slow-blow, precision, and time-delay versions. It usually has a clear glass enclosure (Figure 1).

Figure 1 The glass-body 3AG fuse is among the most widely used in older consumer products as well as older and current chassis-based instrumentation and equipment. Source: Codrey Electronics

However, shatter-proof ceramic ones are also available; one of the handy features of the glass-body version is that you can tell at a glance if it has been blown (Figure 2).

Figure 2 It’s easy to check the status of the glass-body 3AG fuse. Source: Codrey Electronics

Among the many attributes of the 3AG fuse is that it fits into a fuseholder socket and can be removed, inspected, and replaced without tools, and in a few seconds. Of course, that convenience can lead users to sometimes change it without first finding out why it need replacing: was it due to an eternal surge or because of internal short circuit?

Figure 3 This fuse holder is deigned to be screwed to a mounting surface, and the wires are either connected using slip-on contacts or they are soldered. Source: Keystone Electronics via Digi-Key

The 3AG fuse is supported by a large number of fuseholders, including PCB surface-mount units, discrete-wire models (Figure 3) as well as the very popular panel-mount version often used on the back of a chassis (Figure 4). There are even RFI-shielded holders with a captive cap for applications where you don’t want to lose the cap, which is part of the fuse circuit path (Figure 5).

Figure 4 The panel-mount fuse folder is widely used on chassis, most often on the back panel; this spectrograph project uses one fuse and holder for each of its three independent power rails. Source: University of California Observatories

Figure 5 For rugged applications, this metal 3AG holder has a captive cap, which also maintains chassis EMI/RFI shielding integrity. Source: eBay

Of course, fuses come in many other form factors such as the blade-type widely used in automobiles, nor are they the only circuit-protection component in use. Among the other well-known circuit-protection devices are:

• Metal oxide varistor (MOV)
• Positive temperature coefficient (PTC) thermistor
• Transient voltage suppression (TVS) diode
• Gas discharge tube (GDT)
• Polymer PTC resettable fuse

Like fuses, each of these has a well-defined and appropriate role in providing circuit protection, yet the basic circuit-breaking fusible-link retains its position in many designs due to its combination of consistency, direct action, and irreversibility. In fact, many designs use one or more of the above for highly localized protection, plus a thermal-link fuse as a system-level cutoff if things really go the wrong way. In this sense, the classic fuse acts as a backup and offers extra insurance.

But the classic fusible link design represented but not limited to the 3AG style is not physically compatible with many of today’s compact products units. These products don’t have the room for that fuse, and they don’t have a way for the user to get in there and change the fuse—nor would that be a good idea in many cases.

Now consider a rechargeable Li-ion battery pack with its requisite battery management system (BMS): if things really get out of control, having a fuse to terminate current flow is a desirable extra layer of protection. Furthermore, it’s a good idea to figure out what happened and why before you’d want to replace the fuse and re-initiate the current flow.

To meet the size needs and non-replaceable preferences while retaining the virtues of a “hard” fuse and circuit break, vendors are now offering surface-mount fuses as tiny, PCB-friendly components that provide the same level of current-cutoff circuitry as the classic fusible link like 3AG. They do this not by further miniaturization of the traditional thermal element. Instead, they use a variety of innovative structures and technologies.

For example, Bourns has the SinglFuse product portfolio, which comprises seven different fuse-construction technologies: thin-film sputtering, thin-film PCB, ceramic multilayer, ceramic cavity laminate, wire core, ceramic tube, and ceramic cube (Figure 6).

Figure 6 It takes a variety of underlying technologies to create surface-mount, regulatory approved fuses that can handle currents across a wide range. Source: Bourns via Digi-Key

The package sizes of these thermal devices range from an almost invisible 0402—0.040 inch × 0.020 inch or 1.0 mm × 0.5 mm—at the lower current ranges to 3812—0.150 inch × 0.100 inch or 3.81 mm × 2.54 mm—at current ratings of 62 mA to 100 A. Despite their diminutive size, they are UL/CSA/IEC approved, and some models are also AEC-Q200 qualified for automotive use.

I’ll be honest: I’m going to miss the widespread use of the 3AG fuse. I know it’s not going away since it still is the best fit for many application scenarios. However, I will also have to be on the lookout for fuses that look like any other surface-mount device, and it won’t be easy to identify or replace them when there’s a problem.

Plus, there’s something satisfying at a visceral level, seeing how 3AG fuse pulling it from the holder to check it and replace it if needed. Maybe it’s a “caveman/fire/take action” thing? Nonetheless, times and technologies need change, even for humble devices such as fuses.

Which circuit-protection devices, including thermal fuses, have you used? Have you used a combination of different circuit protection devices in your design? Was it a prudent design to meet safety standards? Tell us about your preferences and experiences.

Bill Schweber is an EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features.

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In my recent coverage of balanced headphone connections, I planned to mention the iPhone, despite the fact that neither it nor any other smartphone that I’m aware of—past, current, or announced future—even offers a balanced analog audio output. And ever since the iPhone 7 generation, iPhones don’t support analog audio outputs at all. So your puzzlement on this topic would be understandable, but I never said that the iPhone or other smartphone would be used standalone in balanced mode.

To begin, let’s step back. If your device doesn’t have a built-in analog headphone jack (whether balanced or unbalanced, i.e., single-ended), you’re not out of luck with respect to being able to listen to (along with generate, if microphone functionality is also supported) music and other sounds with it. One option, if your device supports Bluetooth, is to pick up a pair of wireless headphones, but to do so you’ll need to shell out even more cash than you’ve already spent on any headphones you already own. The new ones may not be as high-quality as those you already have, either. And quality may be further compromised depending on which audio codecs are supported both by the Bluetooth transmitter (in the source device) and receiver (headphones).

Option #2: If your audio source device has digital I/O (various forms of USB along with, for iOS devices, Lightning, are the most common options here), and if that digital I/O supports the transport of digital audio (Apple’s Lightning-equipped iPod nano, for example, does not), then you can mate a set of analog headphones to the device in conjunction with an appropriately connector-equipped D/A converter. Apple’s Lightning to 3.5mm headphone jack adapter, for example, doesn’t support a balanced output option, but its sonic performance is reportedly still pretty good. And Google offers a conceptually-similar counterpart for USB-C-equipped gear. Plenty of third-party options also exist, at various price and claimed-quality points. But they’re all limited by a few factors that are out of their fundamental control.

Many audio-capable digital outputs in computers, smartphones, and the like, along with their analog audio outputs, are restricted to no better than “Red Book Audio” quality (i.e., 16-bit per-channel sample sizes and a 44.1 kHz sampling rate; 48 kHz is sometimes alternatively-or-also supported). Apple’s Mac computers’ USB ports can do 24-bit sample sizes and 48 kHz sampling rates, as can the company’s mobile devices’ Lightning ports, but audiophiles still sniff with disdain at such plebeian parameters.

These restrictions are not normally the result of system hardware limitations (after all, an uncompressed Red Book Audio bitstream is ~1.4 Mbps, whereas the USB 2.0 peak theoretical transfer rate is 480 Mbps), but are created by operating systems and drivers, which resample source audio streams prior to mixing them together and outputting them over the analog and digital audio output connections. Bluetooth system software suites frequently do similar undesirable audio transforms.

The third option, and the path I’ve chosen to travel, strives to bypass all of the above limitations as much as possible. It begins with, for my Android smartphones, an application called USB Audio Player Pro, also commonly referred to by its UAPP acronym (related discussion on the Head-Fi enthusiast site may also be of interest). As originally developed, UAPP is intended for use with smartphones that have built-in high-quality audio subsystems, like the LG ones I mentioned in my prior coverage. Reflective of the “USB” in the product name, UAPP can also be used with an external tethered DAC, subject to any interface hardware bitrate limitations. And UAPP’s proficiency has now also expanded to cover wireless (i.e., Bluetooth) connections to an external DAC.

In all cases, UAPP’s overall aspiration is to bypass Android’s various bundled audio processing facilities, thereby keeping the audio as bit-accurate and otherwise pristine as possible all the way from the streamed or file-stored source to your ears. As such, it even bundles an integrated Tidal client, including an optional MQA (Master Quality Authenticated) format decoder, for use with the Tidal HiFi service I mentioned a few months back.

Unsurprisingly, given the topic of this post, I’m using UAPP over Bluetooth. On one end of the wireless link (at least currently) are my two Google Pixel 3a smartphones, which ironically still include unbalanced analog headphone jacks. The eventual successor for one of them is the Pixel 4, which my wife got me for our recent anniversary and which I’m sure I’ll have more to say about in future blog posts. The Pixel 4, like its modern iPhone counterparts, does not have an analog headphone output, thereby bolstering the appeal of the Bluetooth-based alternative.

On the other end of the wireless link is a battery-powered portable Bluetooth receiver, the Earstudio ES100 MK2, from a company called Radsone (which currently also sells a USB-only DAC and a set of in-ear headphones). I first stumbled across the ES100 MK2 earlier this summer as I was browsing through Drop’s then-current product inventory (the related and extensive discussion on the product both there and at Head-Fi.org may also be of interest). I’ll start with some stock photos:

The ES100 MK2 can also operate in a USB-tethered fashion as a wired DAC:

Now it’s time for my shots, the first as-usual-accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison:

As you can see, the ES100 MK2 is pretty tiny: 1×2×0.5 inches, to be exact, with a weight of 20 grams. The packaging is equally diminutive, not to mention unpretentious. The ES100 MK2 product page includes links to multiple in-depth documents in PDF format, which I commend to your inspection.

Here’s the ES100 MK2 alongside my unbalanced Shure E5C in-ear monitors (IEMs), mentioned in my earlier balanced headphones post, my Etymotic Research ER4SR IEMs (complete with ear wax, I now see in re-looking at the photo, yuck sorry about that!) with the balanced cable configuration option, my unbalanced Massdrop X E-MU Purpleheart closed-back headphones (another recent anniversary gift), and my Massdrop x Sennheiser HD 58X Jubilee open-back headphones, also with a supplemental balanced cable:

Claimed battery life is 14 hours, dependent in part on what Bluetooth codec (and resultant required computational horsepower) is in use, the listening volume, what audio processing features are enabled, and other variables. This seems to jive with my limited usage so far, as well as the experiences of the HeadFi.org crowd. Speaking of which, the Android (shown) and iOS applications’ exposed feature sets are extensive:

The ES100 MK2 sounds great when paired with any of the earlier mentioned headphones, especially in balanced configurations, and can even drive my higher-impedance Massdrop x Sennheiser HD 6XX headphones to more-than-sufficient volume levels. It even embeds a microphone, so you can take (and make) calls while your phone is Bluetooth-connected to it. And the clincher is the price tag. I bought the ES100 MK2 from Drop back in October for $75 using a $10-off promotion coupon code (plus taxes, and $5 for shipping). As I type these words on Christmas Eve 2020, it’s selling on Radsone’s site for that same $75, and for $69.99 at Amazon. That’s a non-costly audio upgrade if I ever saw (and heard) one!

Do I wish the ES100 MK2 was made of metal, versus plastic? Conceptually, yes, although looking at the situation from an engineering mindset, I also realize that doing so would likely adversely affect the transmitter-to-receiver operating range (due to the well-known Faraday cage effect). And to that point, I should also point out that the “MK2” in the product name reflects a second-generation mechanical redesign with improved operating buttons and other enhancements (but the same electronics inside).

And do I wish the ES100 MK2 had a user-replaceable battery to avoid its sooner-or-later demise? Yes, but I also realize that doing so would adversely affect the unit’s size, weight, and cost. And pragmatically, after two years’ (or so) use, I’ll probably be ready for an upgrade anyway. The lead designer for the ES100 subsequently left Radsone for Qudelix; the company’s Qudelix-5K Bluetooth-and-USB DAC (whose artwork I used in my earlier balanced headphones piece, more foreshadowing!) has upgraded internals now also supporting, for example, the “Adaptive” variant of the aptX codec and currently sells for only $109 on Amazon.

All in all, I’m quite pleased with my purchase. With that, here’s even more foreshadowing: in my next post, I plan to further discuss the audio codec (for both archive, streaming, and Bluetooth transmission) topics I touched on here. And with that, I’ll wrap up for now and await your thoughts in the comments!

—Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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