RF Burns And Exploding PC Speakers: Sophos Looks At The Evidence

June 21, 2021 by Jenny List 24 Comments

Every year in the month of June, someone by the unlikely name of [R.F. Burns] posts a question to the Linux Kernel Mailing List asking whether a Linux kernel module is possible that would blow the PC speaker. It’s fairly obviously a joke, which is why the UK-based anti-virus company Sophos have devoted a light-hearted blog post to it.

The post is an interesting diversion into early PC sounds, when the only hardware guaranteed to be present was a small speaker hooked up to a bit on an output port. The bit could be cycled for square wave beeps, or with a lot of clever manipulation could put out a low-bitrate PWM that delivered almost intelligible sounds including music and voice. They conclude that since the speaker would have been designed to be at the full amplitude of the 5-volt output bit all the time it should be impossible to blow it from software, and we’d be inclined to agree. There’s a remote possibility that some speakers might have a resonant frequency that could be found in software, but we’re not entirely convinced.

Your Hackaday scribe might have spent a while in a university computer lab back in the day trying and failing to write C code that would produce a usable PWM on an XT speaker, but those with long memories might recall the PC speaker driver for Windows 3.1. If you’re a fan of chiptune music there are even entire albums written for this most basic of instruments.

Header image: MKFI, Public domain.

A Mini USB Display For Your PC Desktop

June 20, 2021 by Jenny List 22 Comments

By now it’s likely that most Hackaday readers will be used to USB display adapters, in their most common form channeling DisplayPort over the ubiquitous serial interface. Connecting to projectors and other screens with a laptop becomes a breeze, and gone are the days of “Will my laptop work in the venue” stress for people delivering presentations. [Avra Mitra]’s STM32 tiny monitor may not ascend to these giddy heights, but it does at least live up to the promise of reproducing a desktop onto a small colour LCD hooked up through a USB port.

Not through any DisplayPort wizardry though, instead it relies on a Python script that takes successive screen grabs and streams them through USB to the microcontroller, which in tun puts them on the display. It’s claimed to achieve 6 to 7 frames per second as you can see in the video below, with an admission that there remains a huge scope for improvement.

Notwithstanding its limited utility at the moment, we can see that maybe this idea could have its uses in a very basic display after a few improvements. Meanwhile, more conventional monitors take the established route of pairing a dedicated controller board with an LCD panel.

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IPod HiFi Gains New High Notes

June 19, 2021 by Jenny List 1 Comment

The iPod HiFi was a stereo speaker add-on produced by Apple in the mid-2000s for their iPod range, a $300-plus speaker cabinet with twin drivers per channel, an iPod dock, aux, and TOSLINK interfaces. It’s caught the eye of [Jake], in particular one posted on Reddit that had an extra set of tweeters to improve the HiFi’s lackluster treble. The question was that it might have been an Apple prototype, but lacking his own [Jake] set out to replicate it.

The job he’s done is to a high quality. The baffle has first 3D scanned, and then recesses were milled out of it so the tweeters could be press-fit in. He’s driving them through a simple LC crossover circuit taken from the speaker drive, and reports himself happy with the result.

Unfortunately, we still don’t know whether or not the Reddit original was an Apple prototype or not. We’d be inclined to say it isn’t and praise the skills of the modder who put the tweeters in, but in case it might be we’d point to something that could deliver some clues. The iPod HiFi didn’t use a passive crossover, instead it had a DSP and active crossover, driving four class D amplifiers. If you find one with tweeters and they’re driven from the DSP through an extra pair of amplifiers then put it on eBay as a “RARE BARN FIND APPLE PROTOTYPE!” and make a fortune, otherwise simply sit back and enjoy the extra treble a previous owner gave it.

Of course, some people baulked at the price tag of the Apple speaker, and made their own.

Vacuum Tube Magic Comes To The 741

June 19, 2021 by Jenny List 41 Comments

Some of you may remember a recent project that featured on these pages, a 555 timer reproduced using vacuum tubes. Its creator [Usagi Electric] was left at loose ends while waiting for a fresh PCB revision of the 555 to be delivered, so set about creating a new vacuum tube model of a popular chip, this time the ubiquitous 741 op-amp. (Video, embedded below.)

The circuit is fairly straightforward, using six small pentodes. The first two are a long-tailed pair as might be expected, followed by two gain stages, then a final gain stage feeding a cathode follower with feedback. It’s neatly built on a PCB with IC-style “pins” made from more PCB material, then put in a huge replication of an IC socket on a wooden baseboard.

The result is an op-amp, but not necessarily a good one. He looks at the AC performance instead of the DC even though it’s a fully DC-coupled circuit, and finds that while it performs as expected in a classic op-amp circuit it still differs from the ideal at higher gain. The frequency response is poor too, something he rectifies by replacing the feedback capacitor with a smaller value. Sadly he doesn’t look at its common mode performance, though we’d expect that without close matching of the tubes it might leave something to be desired.

It’s obvious that this project would never be selected as an op-amp given the quality of even the cheapest silicon op-amp in comparison. But its value is in a novelty, a talking point, and maybe a chance to learn about op-amps. For that, we like it.

We covered the vacuum tube 555 when details of it emerged, but if op-amps are your bag we’ve looked at a simple one very closely indeed.

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Tell Time The Cistercian Way

June 19, 2021 by Jenny List 10 Comments

It’s rare for the fields of the engineer and the mediaevalist to coincide, but there’s a clock project bringing the two fields together. The Cistercian monastic order used an intriguing number system from the 13th century onwards that could represent any four-digit number as a series of radicals expressed in the four corners of a single composite symbol, and it’s this number system that’s used by the clock to render the full range of 24 hour time on a large 5×7 LED matrix mounted on a wooden base.

Behind the scenes is an Arduino and a DS3231 real-time clock, and all the code can be found in a handy GitHub repository. There’s even a PCB from everyone’s favourite vendor of purple PCBs, The result is certainly an interesting clock that makes the break from the usual binary and Nixie timepieces with some style. It also provides an introduction to this fascinating but obscure numerical system, in the event that any of us might have missed the one other such clock that has made it to these pages.

Is It A Plasma Tweeter Or A Singing Tesla Coil?

June 19, 2021 by Jenny List 6 Comments

When our ears resolve spatial information, we do so at the higher treble frequencies rather than the bass. Thus when setting up your home cinema you can put the subwoofer almost anywhere, but the main speakers have to project a good image. The theoretical perfect tweeter for spatial audio is a zero mass point source, something that a traditional speaker doesn’t quite achieve, but to which audio engineers have come much closer with the plasma tweeter. This produces sound by modulating a small ball of plasma produced through high-voltage discharge, and it’s this effect that [mircemk] has recreated with his HF plasma tweeter.

A look at the circuit diagram and construction will probably elicit the response from most of you that it looks a lot like a Tesla coil, and in fact that’s exactly what it is without the usual large capacitor “hat” on top. This arrangement has been used for commercial plasma tweeters using both tubes and semiconductors, and differs somewhat from the singing Tesla coils you may have seen giving live performances in that it’s designed to maintain a consistent small volume of discharge rather than a spectacular lightning show to thrill an audience.

You can see it in operation in the video below the break, and it’s obvious that this is more of a benchtop demonstration than a final product with RF shielding, It’s not the most efficient of devices either, but given that audiophiles will stop at nothing in their pursuit of listening quality, we’d guess that’s a small price to pay. Efficiency can be improved with a flyback design, but for the ultimate in showing off how about a ring magnet to create the illusion of a plasma sheet?

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Do You SpaceAPI?

June 18, 2021 by Jenny List 8 Comments

Here at Hackaday we’re privileged to be part of a global community of hackers, makers, technology enthusiasts and creative people whose collective works make our daily news feeds such a fascinating read. We encounter you all directly in the physical world rather the virtual one at the many events across the community, or at the various hackerspaces we visit on our travels. But how can we keep track of the world of hackerspaces when there are so many? Maybe SpaceAPI might hold the answer.

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