If there’s one thing that amateur radio operators are passionate about, it’s the search for the perfect sine wave. Oscillators without any harmonics are an important part of spectrum hygiene, and while building a perfect oscillator with no distortion is a practical impossibility, this twin-tee audio frequency oscillator gets pretty close.
As [Alan Wolke (W2AEW)] explains, a twin-tee oscillator is quite simple in concept, and pretty simple to build too. It uses a twin-tee filter, which is just a low-pass RC filter in parallel with a high-pass RC filter. No inductors are required, which helps with low-frequency designs like this, which would call for bulky coils. His component value selections form an impressively sharp 1.6-kHz notch filter about 40 dB deep. He then plugs the notch filter into the feedback loop of an MCP6002 op-amp, which creates a high-impedance path at anything other than the notch filter frequency. The resulting sine wave is a thing of beauty, showing very little distortion on an FFT plot. Even on the total harmonic distortion meter, the oscillator performs, with a THD of only 0.125%.
This video is part of [Alan]’s “Circuit Fun” series, which we’ve really been enjoying. The way he breaks complex topics into simple steps that are easy to understand and then strings them all together has been quite valuable. We’ve covered tons of his stuff, everything from the basics of diodes to time-domain reflectometry.
Once ubiquitous, the incandescent light bulb has become something of a lucerna non grata lately. Banned from home lighting, long gone from flashlights, and laughed out of existence by automotive engineers, you have to go a long way these days to find something that still uses a tungsten filament.
Strangely enough, this lamp-stabilized LM386 Wien bridge oscillator is one place where an incandescent bulb makes an appearance. The Wien bridge itself goes back to the 1890s when it was developed for impedance measurements, and its use in the feedback circuits of vacuum tube oscillators dates back to the 1930s. The incandescent bulb is used in the negative feedback path as an automatic gain control; the tungsten filament’s initial low resistance makes for high gain to kick off oscillation, after which it heats up and lowers the resistance to stabilize the oscillation.
For [Grug Huler], this was one of those “just for funsies” projects stemming from a data sheet example circuit showing a bulb-stabilized LM386 audio oscillator. He actually found it difficult to source the specified lamp — there’s that anti-tungsten bias again — but still managed to cobble together a working audio oscillator. The first pass actually came in pretty close to spec — 1.18 kHz compared to the predicted 1.07 kHz — and the scope showed a very nice-looking sine wave. We were honestly a bit surprised that the FFT analysis showed as many harmonics as it did, but all things considered, the oscillator performed pretty well, especially after a little more tweaking. And no, the light bulb never actually lights up.
Thanks to [Grug] for going down this particular rabbit hole and sharing what he learned. We love builds like this that unearth seemingly obsolete circuits and bring them back to life with modern components. OK, calling the LM386 a modern component might be stretching things a bit, but it is [Elliot]’s favorite chip for a reason.
Back in the “beige box” days of computing, it was pretty easy to tell what your machine was doing just by listening to it, because the hard drive was constantly thrashing the heads back and forth. It was sometimes annoying, but never as annoying as hearing the stream of Geiger counter-like clicks stop when you knew it wasn’t done loading a program yet.
That “happy sound” is getting harder to come by, even on retro machines, which increasingly have had their original thrash-o-matic drives replaced with compact flash and other solid-state drives. This HDD sound simulator aims to fill that diagnostic and nostalgic gap on any machine that isn’t quite clicky enough for you. Sadly, [Matthias Werner] provides no build details for his creation, but between the longish demo video below (by a satisfied customer) and the details of the first version, it’s easy enough to figure out what’s going on here. An ATtiny and a few support components ride on a small PCB along with a piezoelectric speaker. The dongle connects to the hard drive activity light, which triggers a series of clicks from the speaker that sound remarkably like a hard drive heading seeking tracks. A demo starts at 7:09 in the video below; the very brave — or very nostalgic — might want to check out the full defragmentation that starts at 13:11.
Sure, this one is perhaps a bit over-the-top, but in the retrocomputing world, no price is too high to pay in the name of nostalgia. And it’s still far from the most ridiculous hard drive activity indicator we’ve seen.
Tell the world that something is in short supply, and you can bet that people will start reacting to that news in the ways that make the most sense to them — remember the toilet paper shortage? It’s the same with the ongoing semiconductor pinch, except that since the item in short supply is (arguably) more valuable than toilet paper, the behavior and the risks people are willing to take around it are even more extreme. Sure, we’ve seen chip hoarding, and a marked rise in counterfeit chips. But we’d imagine that this is the first time we’ve seen chip smuggling quite like this. The smuggler was caught at the Hong Kong-Macao border with 256 Core i7 and i9 processors, valued at about $123,000, strapped to his legs and chest. It reminds us more of “Midnight Express”-style heroin smuggling, although we have to say we love the fact that this guy chose a power of 2 when strapping these babies on.
Speaking of big money, let’s say you’ve pulled off a few chip heists without getting caught, and have retired from the smuggling business. What is one to do with the ill-gotten gains? Apparently, there’s a big boom in artifacts from the early days of console gaming, so you might want to start spreading some money around there. But you’d better prepare to smuggle a lot of chips: last week, an unopened Legend of Zelda cartridge for the NES sold for $870,000 at auction. Not to be outdone, two days later someone actually paid $1.56 million for a Super Mario 64 cartridge, this time apparently still in the tamperproof container that displayed it on a shelf somewhere in 1996. Nostalgia can be an expensive drug.
And it’s not just video games that are commanding high prices these days. If you’ve got a spare quarter million or so, why not bid on this real Apollo Guidance Computer and DSKY? The AGC is a non-flown machine that was installed in LTA-8, the “lunar test article” version of the Landing Module (LM) that was used for vacuum testing. If the photos in the auction listing seem familiar, it’s with good reason: this is the same AGC that was restored to operating condition by Carl Claunch, Mike Stewart, Ken Shiriff, and Marc Verdiell. Sotheby’s estimates the value at $200,000 to $300,000; in a world of billionaire megalomaniacs with dreams of space empires, we wouldn’t be surprised if a working AGC went for much, much more than that.
Meanwhile, current day space exploration is going swimmingly. Just this week NASA got the Hubble Space Telescope back online, which is great news for astronomers. And on Mars, the Ingenuity helicopter just keeps on delivering during its “operations demonstration” mission. Originally just supposed to be a technology demonstration, Ingenuity has proven to be a useful companion to the Perseverance rover, scouting out locations of interest to explore or areas of hazard to avoid. On the helicopter’s recent ninth flight, it scouted a dune field for the team, providing photographs that showed the area would be too dangerous for the rover to cross. The rover’s on-board navigation system isn’t great at seeing sand dunes, so Ingenuity’s images are a real boon to mission planners, not to mention geologists and astrobiologists, who are seeing promising areas of the ancient lakebed to explore.
And finally, most of us know all too well how audio feedback works, and all the occasions to avoid it. But what about video feedback? What happens when you point a camera that a screen displaying the image from the camera? Fractals are what happens, or at least something that looks a lot like fractals. Code Parade has been playing with what he calls “analog fractals”, which are generated just by video feedback and not by computational means. While he’d prefer to do this old school with analog video equipment, it easy enough to replicate on a computer; he even has a web page that lets you arrange a series of virtual monitors on your screen. Point a webcam at the screen, and you’re off on a fractal journey that constantly changes and shifts. Give it a try.
Of all our senses, the sense of touch is perhaps the most underappreciated. We understand and accept the tragedy that attends loss of vision or hearing, and the impact on the quality of life resulting from olfactory and gustatory sensations can be severe. But for some reason, we don’t give a second thought to our sense of touch, which is indeed strange given that we are literally covered with touch sensors. That’s a bit of a shame, since touch can reveal so much about the world around us, and our emotional well-being is so tightly tied to the tactile senses that those deprived of it in infancy can be scarred for life.
Haptics is the technology of tactile feedback, which seeks to leverage the human need for tactile experiences to enrich the experience of dealing with the technological world. Haptic feedback devices are everywhere now, and have gone far beyond the simple off-balance motor used since the days when a pager was a status symbol. To help us sort out what’s new in the haptics world, Tim and Kyle from Nanoport Technology will stop by the Hack Chat. Nanoport is a company on the cutting edge of haptics, so they’ll have a wealth of details about what haptics are, where the field is going, and how you can start thinking about making touch a part of your projects.
Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about. Continue reading “Haptics Hack Chat With Nanoport Technology”→
With global temperatures continuing to break records in recent years, it’s important to cast an eye towards the future. While efforts to reduce emissions remain in a political quagmire, time is running out to arrest the slide into catastrophe.
Further compounding the issue are a variety of positive feedback loops that promise to further compound the problem. In these cases, initial warming has flow-on effects that then serve to further increase global temperatures. Avoiding these feedback mechanisms is crucial if the Earth is to remain comfortably livable out to the end of the century.
A Multitude of Causes
The issue of climate change often appears as a simple one, with the goal being to reduce greenhouse gas emissions in order to prevent negative consequences for human civilization. Despite this, the effects of climate change are often diffuse and intermingled. The various climate systems of the Earth interact in incredibly complex ways, and there are many mechanisms at play in these feedback effects that could tip things over the edge.
It’s the [Bruce Land]-iest season of all, when the Cornell professor submits the projects his microcontroller class students have been working on all semester. Imagination does not seem to be in short supply with these students, and we always look forward to these tips this time of year.
[Greg] and [Sam]’s touch-screen two-dimensional ball balancer is a good example of what [Land]’s students turn out. The resistive touch screen is supported by a 3D-printed gimballed platform and tilted in two axes by hobby servos. [Greg] and [Sam] chose to read the voltage outputs from the touch screen directly using the ADC on a PIC32, toggling between the two axes at 2 kHz. Two PID control loops were implemented to keep the ball as centered as possible on the platform, and the video below shows that there’s still some loop tuning to do. But given the positional inaccuracies of hobby servos and the compliance in the gimbal, we’re impressed that they were able to keep the system under control at all.
