Ken Shirriff Found Butterflies In His Op-Amp

June 27, 2018 by Steven Dufresne 8 Comments

In 1976, Texas Instruments came out with the TL084, a four JFET op-amp IC each with similar circuitry to Fairchild’s very popular single op-amp 741. But even though the 741 has been covered in detailed, when [Ken Shirriff] focused his microscope on a TL084, he found some very interesting things.

To avoid using acid to get at the die, he instead found a ceramic packaged TL084 and pried off the cover. The first things he saw were four stabilizing capacitors, by far the largest structures on the die and visible to the naked eye.

When he peered into his microscope he next saw butterfly shapes which turned out to be pairs of input JFETs. The wide strips are the gates and the narrower strip surrounded by each gate is the source. The drain is the narrow strip surrounding each gate. Why arrange four JFETs like this? It’s possible to have temperature gradients in the IC, one side being hotter than the other. These gradients can affect the JFET’s characteristics, unbalancing the inputs. Look closely at the way the JFETs are connected and you’ll see that the top-left one is connected to the bottom-right one, and similarly for the other two. This diagonal cross-connecting cancels out any negative effects.

[Ken’s] analysis in his article doesn’t stop there though. Not only does he talk more about these JFETs but he goes over the rest of the die too. It’s well worth the read, as is his write-up about the 741 which we’ve also covered.

PIC Powered PicoBat Picks Up Pulsed Power

June 26, 2018 by Kerry Scharfglass 15 Comments

In 2012, [Bruno] wanted to detect some bats. Detect bats? Some varieties of bat (primarily the descriptively named “microbats”) locate themselves and their prey in space using echolocation, the same way your first robot probably did. The bat emits chirps from their adorably tiny larynx the same way a human uses its vocal cords to produce sound. The bat then listens for an echo of that sound and can make inferences about the location of its presumed prey in the volume around it. Bat detectors are devices which can detect these ultrasonic sounds and shift them into a range that humans can hear. So how would you build such a device? [Bruno]’s PicoBat probably sets the record for component count and code simplicity.

With no domain expertise the most conspicuous way to build a bat detector is probably to combine the glut of high performance microcontrollers with a similarly high performing analog to digital converter. With a little signal processing knowledge you sample the sounds at their native frequency, run them through a Fast Fourier transform, and look for energy in the ultrasonic frequency range, maybe about 20 kHz to 100 kHz, according to Wikipedia. With more knowledge about signal interference it turns out there are a surprisingly large number of ways to build such a device, including some which are purely analog. (Seriously, check out the Wikipedia page for the myriad ways this can be done.)

[Bruno] did use a microcontroller to build his bat detector, but not in the way we’d have expected. Instead of using a beastly high performance A/D and a similarly burly microcontroller, the PicoBat has a relatively tame PIC12 and a standard ultrasonic transducer, as well as a piezo buzzer for output. Along with a power rail, that’s the entire circuit. The code he’s running is similarly spartan. It configures a pair of GPIOs and toggles them, with no other logic. That’s it.

So how does this work? The ultrasonic transducer is designed mechanically to only receive sounds in the desired frequency range. Being piezoelectric, when enough sound pressure is applied the stress causes a small voltage. That voltage is fed into the PIC not as a GPIO but as a clock input. So the CPU only executes an instruction when ultrasonic sound with enough intensity hits the transducer. And the GPIO toggling routine takes four clock cycles to execute, yielding a 1:4 clock divider. And when the GPIOs toggle they flip the potential across the buzzer, causing it to make human-audible sound. Brilliant!

Check out [Bruno]’s video demo after the break to get a sense for how the device works. You might be able to do this same trick with other components, but we’re willing to be that you won’t beat the parts count.

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No Caffeine, No Problem: A Hand-Soldered Chip-Scale Package

June 26, 2018 by Dan Maloney 47 Comments

It’s said that the electronic devices we use on a daily basis, particularly cell phones, could be so much smaller than they are if only the humans they’re designed for weren’t so darn big and clumsy. That’s only part of the story — battery technology has a lot to do with overall device size — but it’s true that chips can be made a whole lot smaller than they are currently, and are starting to bump into the limit of being able to handle them without mechanical assistance.

Or perhaps not, if [mitxela]’s hand-soldering of a tiny ball-grid array chip is any guide. While soldering wires directly to a chip is certainly a practical skill and an impressive one at that, this at least dips its toe into the “just showing off” category. And we heartily endorse that. The chip is an ATtiny20 in a WLCSP (wafer-level chip-scale package) that’s a mere 1.5 mm by 1.4 mm. The underside of the chip has twelve tiny solder balls in a staggered 4×6 array with 0.4 mm pitch. [mitxela] tackled the job of soldering this chip to a 2.54-mm pitch breakout board using individual strands from #30 AWG stranded wire and a regular soldering iron, with a little Kapton tape to hold the chip down. Through the microscope, the iron tip looks enormous, and while we know the drop of solder on the tip was probably minuscule we still found ourselves mentally wiping it off as he worked his way across the array. In the end, all twelve connections were brought out to the protoboard, and the chip powers up successfully.

We’re used to seeing [mitxela] work at a much larger scale, like his servo-plucked music box or a portable Jacob’s Ladder. He’s been known to get small before though, too, like with these tiny blinkenlight earrings.

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Dust To Dust And Jello To Jello: The Journey Of A Very Strange Knife

June 25, 2018 by Tucker Ervin 24 Comments

How do you feel about Jello? It’s alright tasting, but it’s much more about how jiggly it gets. Nobody — probably — would eat Jello if it was a hard candy. It would quickly become restricted to the bowl of strawberry candies that Grandma always seems to have. How do you feel about knives? We’re on Hackaday. Most everybody here has at least a couple in their toolbox. Some of them have more than a couple, including the whetstones to sharpen them. It’s safe to say they probably like the concept. Now, what if you could combine the two? Two favorites are always better than one. A Jello knife, while seemingly impossible, would be rather impressive, and [kiwami japan] does just that, as well as so much more.

He starts with a couple dozen adorable Jello snacks (Jellos?), and from the wiggliest of foundations, he builds a masterpiece. The first order of business is to eat a couple of the stragglers while he decides what to do with the rest. A bit of blue food coloring, some more gelatin, and the help of several cow shaped bowls and pitchers later, [kiwami japan] has melted the survivors down and gotten a flat sheet. Once sufficiently cooled, it makes a nice knife-shaped Jello blank.

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Lawn From Hell Saved By Mower From Heaven

June 19, 2018 by Kristina Panos 94 Comments

It’s that time of year again, at least in the northern hemisphere. Everything is alive and growing, especially that narrow-leafed non-commodity that so many of us farm without tangible reward. [sonofdodie] has a particularly hard row to hoe—his backyard is one big, 30° slope of knee-ruining agony. After 30 years of trudging up and down the hill, his body was telling him to find a better way. But no lawn service would touch it, so he waited for divine inspiration.

And lo, the answer came to [sonofdodie] in a trio of string trimmers. These Whirling Dervishes of grass grazing are mounted on a wheeled plywood base so that their strings overlap slightly for full coverage. Now he can sit in the shade and sip lemonade as he mows via rope and extension cord using a mower that cost about $100 to build.

These heavenly trimmers have been modified to use heavy nylon line, which means they can whip two weeks’ worth of rain-fueled growth with no problem. You can watch the mower shimmy down what looks like the world’s greatest Slip ‘n Slide hill after the break.

Yeah, this video is two years old, but somehow we missed it back then. Ideas this fresh that tackle age-old problems are evergreen, unlike these plots of grass we must maintain. There’s more than one way to skin this ecological cat, and we’ve seen everything from solar mowers to robotic mowers to mowers tied up to wind themselves around a stake like an enthusiastic dog.

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Hybrid Lab Power Supply From Broken Audio Amp

June 18, 2018 by Ben James 9 Comments

The lab power supply is an essential part of any respectable electronics workbench. However, the cost of buying a unit that has all the features required can be eye-wateringly high for such a seemingly simple device. [The Post Apocalyptic Inventor] has showed us how to build a quality bench power supply from the guts of an old audio amplifier.

We’ve covered our fair share of DIY power supplies here at Hackaday, and despite this one being a year old, it goes the extra mile for a number of reasons. Firstly, many of the expensive and key components are salvaged from a faulty audio amp: the transformer, large heatsink and chassis, as well as miscellaneous capacitors, pots, power resistors and relays. Secondly, this power supply is a hybrid. As well as two outputs from off-the-shelf buck and boost converters, there is also a linear supply. The efficiency of the switching supplies is great for general purpose work, but having a low-ripple linear output on tap for testing RF and audio projects is really handy.

The addition of the linear regulator is covered in a second video, and it’s impressively technically comprehensive. [TPAI] does a great job of explaining the function of all the parts which comprise his linear supply, and builds it up manually from discrete components. To monitor the voltage and current on the front panel, two vintage dial voltmeters are used, after one is converted to an ammeter. It’s these small auxiliary hacks which make this project stand out – another example is the rewiring of the transformer secondary and bridge rectifier to obtain a 38V rail rated for twice the original current.

The Chinese DC-DC switching converters at the heart of this build are pretty popular these days, in fact we’re even seeing open source firmware being developed for them. If you want to find out more about how they operate on a basic level, here’s how a buck converter works, and also the science behind boost converters.

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Building An Ultralight In A Basement Is Just So Beautiful To See

June 16, 2018 by Brian Benchoff 15 Comments

[Peter] is at it again. Not content with being one of the best RC confabulators on YouTube, and certainly not content with the first airplane he built in his basement, [Peter Sripol] is building another airplane in his basement.

The first airplane he built was documented on YouTube over a month and a half. It was an all-electric biplane, built from insulation foam covered in fiberglass, and powered by a pair of ludicrously oversized motors usually meant for large-scale RC aircraft. This was built under Part 103 regulations — an ultralight — which means there were in effect no regulations. Anyone could climb inside one of these without a license and fly it. The plane flew, but there were a few problems. It was too fast, and the battery life wasn’t really what [Peter] wanted.

Now [Peter] is onto his next adventure. Compared to the previous plane, this has a more simplified, traditional construction. It’s a high wing monoplane with an aluminum frame. There are two motors again, although he’s still in the process of finding lower kV motors. This plane should also fly slower, longer, something you really want in an ultralight.

As far as tools required for this build, it’s surprising how few are needed to put the plane together. Of course, there are a few excessively large pop rivet guns and there will be some extra special aviation-grade bolts, but the majority of this plane will be made out of standard aluminum, insulation foam, a bit of wood, and some fiberglass. Watching [Peter] churn out high-end fabrication with these simple parts is so satisfying. If you have a drill press with a cross slide vise, you too can build a plane in your basement.

This is shaping up to be a truly fantastic build. [Peter] has already proven that yes, he can indeed build an airplane in his basement. This time, though, he’s going to have a plane that will stay in the air for more than just a few minutes.

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