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This is part of IEEE Spectrum’s special report: Top 11 Technologies of the Decade
Even in the go-go world of high tech, it’s pretty rare that a technological leap delivers both markedly superior performance and stunningly greater efficiency. That neat trick happened with class-D audio amplifiers, which now dominate the market for applications in car stereos, home-theater-in-a-box systems, television sets, and personal computers.
Their success has been a long time coming. The first commercially available class-D amps came in the 1960s from the British company Sinclair Radionics (now Thurlby Thandar Instruments), but they didn’t work well. Somewhat better ones came along in the 1970s and 1980s: John Ulrick designed a couple of class-D amps for Infinity Systems in the early and mid-1970s, and a decade later Brian Attwood did a series of “digital energy conversion amplifiers” for Peavey Electronics Corp. But in those days class-D theory was ahead of implementation, because the available components simply weren’t good enough to produce high-quality sound.
The problem was speed: Class-D amps sample the input audio waveform hundreds of thousands of times a second before amplifying it, and it wasn’t until the 1990s that cheap and reliable MOSFETs became available that were fast enough to sample a waveform at such high frequencies, says Bruno Putzeys, the chief engineer at Hypex Electronics. Hypex, in Groningen, Netherlands, is a leading maker of audiophile class-D amplifier modules, which are incorporated into products sold by other firms.
“What it took was for a couple of companies to take the plunge,” Putzeys adds. Those pioneers were Tact Audio, ICEpower, and Tripath Technology, all of which released their first class-D offerings in the late 1990s. Tact, now called Lyngdorf, rocked the audio community in 1998 with a US $9800 class-D amplifier called the TacT Millennium, which was designed by the Danish engineer Lars Risbo. It dazzled as much for its industrial design as for its engineering: The amp had a large volume knob with a digital display in its center.
COMPANY TO WATCH: Intersil D2Audio, Milpitas, Calif. Intersil D2Audio sells products powered by its Digital Audio Engine technology, which combines class-D amplifiers with signal processing to minimize the effects of noisy power supplies or harsh automotive environments.
BET YOU DIDN’T KNOW: The first class-D audio amplifier offered to the public, in 1964, was an £8 kit from the British company Sinclair Radionics. Its power output was so far below the claimed 10 watts that Wireless World magazine, deluged with complaints, supposedly declined to take future advertising from Sinclair.
ICEpower was founded jointly by another Danish engineer, Karsten Nielsen, who designed the company’s first amplifiers and amplifier modules, and the Danish audio company Bang & Olufsen. ICEpower is best known for its combined power supply and amplifier modules, although its single biggest source of income is its MobileSound line of amplifier chips for cellphones.
Tripath, in San Jose, Calif., was the first to introduce a class-D amplifier chip, the TA1101, in 1996. It was used in Apple’s celebrated Power Mac G4 Cube. Tripath’s first big hit, the TA2020, in 1998, could funnel 20 watts per channel into 4-ohm speakers (see “25 Microchips That Shook the World”). It was used in ministereos and early flat-screen TVs. “We were shipping millions of chips every quarter to companies like Samsung, Panasonic, Toshiba, Sanyo, NEC, Onkyo, and Sony,” says Adya Tripathi, who was the company’s president and CEO.
Large stocks of Tripath chips are still available. They feed an e-Bay market for tiny, ultracheap (as low as $15) amps from China and also a thriving business among hobbyists and DIYers.
Today almost all of the audio amplifier market, from cheap cellphone chips to unbelievably expensive home hi-fi, is split between class-D and class-AB amplifiers; the latter are the long-established technology, and they still dominate in home audio and also in mobile music players, including iPods, MP3s, and smartphones. Those pocket players use micropower amps, which put out fewer than 100 milliwatts per channel. Class-D chips are available for these applications, but they can’t yet match the price of the class-AB chips that are available for a few cents per chip from such giants as National Semiconductor, Maxim, Texas Instruments, Sanyo, and various Taiwanese companies. Millions of those amps are sold every year. And class-AB isn’t even the only other competitor in this fast-growing field: Class-G amp chips share class-D’s high efficiency and are also supposedly easier to integrate into a dense and highly complicated system like a smartphone.
Nevertheless, the micropower category is still a big market possibility for class-D chips, Tripathi insists. It’s only a matter of time before the huge efficiency advantage of class-D tips the scales in their favor, just as class-AB amps slowly but surely displaced class-A decades ago. Some day, without a doubt, it will be a class-D world.
In the meantime, class-D amps are making steady inroads in the home market, where they can exploit to full advantage modern components that are cheap but have very high performance: MOSFETs just keep getting better and better and cheaper and cheaper. And for the technically inclined, amplifier modules and kits allow anyone with modest soldering skills to get class-D sound, highly precise and detailed, for a few hundred dollars. One of our favorite kits is the SDS-224 kit from Class D Audio, with its robust power supply.
Class-D amps are starting to do well even in the rarefied high-end niche, where an amplifier can cost many thousands of dollars. Putzeys just completed and tested an amplifier design with total harmonic distortion of 0.001 percent at full power across the entire audio range, scalable to 2000 W and beyond. It is a specification that would have been dismissed as science fiction before class-D amplifiers. At any price.
For all of IEEE Spectrum’s Top 11 Technologies of the Decade, visit the special report.
The Ethereum-blockchain-based app already has thousands of riders and drivers, but challenges remain
Edd Gent is a freelance science and technology writer based in Bangalore, India. His writing focuses on emerging technologies across computing, engineering, energy and bioscience. He's on Twitter at @EddytheGent and email at edd dot gent at outlook dot com. His PGP fingerprint is ABB8 6BB3 3E69 C4A7 EC91 611B 5C12 193D 5DFC C01B. His public key is here. DM for Signal info.
Drife’s cofounders are chief operating officer Surya Ranjith [left], chief executive officer Firdosh Sheikh [middle], and chief technology officer Mudit Marda [right].
Ride-hailing in India is dominated by Uber and local rival Ola, but startup Drife thinks blockchain technology could be the key to breaking up their duopoly.
CEO and cofounder Firdosh Sheikh used to be a power user of Uber, racking up more than 5,000 rides in total. But after speaking to drivers she discovered many were unhappy with the commissions the platform charged and the often opaque rules that governed which rides they get assigned. Riders also get a raw deal, she says, with little control over what they pay for their rides or who they travel with.
The problem, Sheikh decided, boiled down to having a middleman controlling the relationship between riders and drivers. So she set out to build a decentralized ride-hailing platform that puts control back into the hands of users via blockchain technology. Last November, after three years of development, she and her cofounders launched the Drife app in the southern city of Bangalore. Today, they have more than 10,000 drivers and 100,000 riders signed up to the platform.
One of the main things that differentiates them from companies like Uber, says Sheikh, is that they don’t charge any commission. Drivers get to keep the entire fare and will instead pay a monthly subscription to use the platform, although the company is currently waiving this to encourage sign-ups.
“We don’t charge anything from the fare that you pay as a rider,” she says. “A centralized entity who has a profit motive in the fare that I pay as a rider will start manipulating the fare and exploiting it for their own profit motive, and that’s where both drivers and riders struggle.”
A base fare is set based on the class of vehicle and the distance of the trip, but after that riders can boost the amount they are willing to pay to attract more drivers. Drivers can also make counteroffers. The rider then chooses who to go with based either on price or driver ratings. This means pricing is purely market-driven, and because Drife isn’t taking a cut, fares should be cheaper than alternatives, says Sheikh.
The company also has its own cryptocurrency, called DRF. At present it can’t be used for much, but the token will play an important role in Drife’s expansion plans, says Sheikh. The company plans to operate on a franchise model, with local entrepreneurs bidding to run Drife operations in new cities in return for a share of subscription fees. But to apply for a franchise, they will need to purchase a large chunk of DRF tokens and lock them up for the duration of their contract. So far the company has received about 60 franchise requests from cities across the world, says Sheikh.
About 30 percent of DRF tokens have also been reserved for an “ecosystem fund,” which will be used for incentives and rewards for drivers and riders. Besides being tradable for real money, these tokens will also confer the right to vote in a decentralized autonomous organization (DAO)—a kind of member-run organization whose internal rules are encoded into a blockchain. Each city will have their own DAO, which will be responsible for choosing franchisees.
“Nothing that we see today can work at the scale that we want to grow,” says Sheikh. “That’s why we’ve started our own side project where we’re working on a blockchain customized to our own needs.”
Crucially, users won’t need to take Drife’s word for any of this, as the entire system will be governed by smart contracts. These are software programs that live inside a blockchain and automate transactions according to predefined rules that are visible to everyone. “Nobody’s going to trust me if I say I don’t manipulate it unless I show them that I don’t have any power to manipulate that data,” says Sheikh. “That’s only possible through blockchain.”
In reality, however, Drife is building the plane while flying it. The firm’s smart-contract system is built on Polygon, which is an extension of the Ethereum blockchain. But because they are constantly tweaking features and functionality, Sheikh admits that most of the time operations are actually running on a back-end server that mimics the processing the blockchain is supposed to do.
And many of the details about how the platform will work still need to be ironed out. How to ensure the DAO voting system isn’t dominated by those who hold the most tokens is a work in progress, says Sheikh. Most blockchains are also geared toward settling financial transactions, and it’s not clear if they can cope with the volume of real-world data involved in running a large-scale ride-hailing business. “Nothing that we see today can work at the scale that we want to grow,” says Sheikh. “That’s why we’ve started our own side project where we’re working on a blockchain customized to our own needs.”
It might still be some time before that becomes a problem. Despite a promising number of sign-ups, the company is currently doing only around 7,000 rides a week, compared to the millions done by Uber and Ola every day.
Mobility consultant Vinay Piparsania, founder of MillenStrat Advisory & Research, says that blockchain technology holds considerable promise for disrupting the ride-hailing industry and breaking the monopolies of the big players. The biggest challenge for startups like Drife, though, is matching their financial and operational capabilities.
“Unfortunately, at this time, such driver-focused startups are much too small and fragmented to make the difference to the duopolic might of Uber and Ola,” he says. It’s a David and Goliath situation, Piparsania adds, so for the time being these companies should focus on “nibbling away in some key towns and categories by attracting and holding onto drivers, and actually demonstrating to riders that they can compete on delivery.”
How to hunt for downed radiosonde beacons with a cheap SDR receiver
David Schneider is a senior editor at IEEE Spectrum. His beat focuses on computing, and he contributes frequently to Spectrum's Hands On column. He holds a bachelor's degree in geology from Yale, a master's in engineering from UC Berkeley, and a doctorate in geology from Columbia.
What goes up must come down, and you might find it after it lands with an inexpensive software-defined radio and homebrew antennas.
I’ve never hadan interest in pursuing game such as deer or grouse. Hunting was never my thing. But I do enjoy a good technical challenge. And I recently found a challenge that involves hunting—with downed radiosondes as the quarry.
Radiosondes are instrument packages carried aloft by weather balloons. They measure atmospheric conditions up to altitudes of 30 kilometers or more, providing key data for the computer models that give us our weather predictions. Weather services around the world launch countless numbers of these balloons. The U.S. National Weather Service (NWS) alone sends them up twice a day from about 100 different locations. During their flights, which can last as long as a few hours, they transmit data by radio. Eventually the balloons ascend so high that the low pressure causes them to burst. The radiosonde package descends, slowed by a small parachute.
Sometimes these radiosondes are found on the ground. The NWS reuses returned radiosondes when it can. Tracking one down and returning it would be a way for me to say, “Thank you” for the essential work the folks there do. My hunting gear would be a pair of homemade antennas and a software-defined radio (SDR).
Another invaluable aid was the Sondehub Tracker website. It’s amazing: You can track the flights of weather balloons around the world in real time using data received by radio amateurs. I’ve been using this site to follow the balloons launched from the airport in Greensboro, N.C., about 70 km from my home. But the radio amateurs who have been tracking balloons launched from Greensboro are located quite far away, and they typically lose contact when the falling radiosonde reaches a few kilometers’ altitude, which leaves considerable uncertainty in the radiosonde’s final position.
You can use an inexpensive software-defined-radio dongle [bottom left] to track radiosondes carried aloft by weather balloons. Even a simple omnidirectional antenna [top left] will serve for that, but a Yagi antenna [middle] provides greater sensitivity and directionality. A laptop runs the software used to analyze the signal, and an orange safety vest reassures onlookers. James Provost
Clearly, I’d need to track these things myself, following them down as close to the ground as possible. Then I could go to my best guess for the landing site and try to pick up the signal from the downed radiosonde—transmitting perhaps from high in a tree (which would no doubt present its own interesting technical challenges).
The balloon data on the Sondehub site shows that the NWS in Greensboro is using Graw DFM-17 radiosondes, transmitting on 403.4 megahertz. To receive these signals, I quickly cobbled together a 1/4-wave antenna (using an online calculator to size the elements), plugged that into an SDR dongle attached to my laptop, and ran the HDSDR software, which I had used for various other projects. In no time, I was picking up FM signals from the balloons being launched from the Greensboro airport at 7 a.m. and 7 p.m. each day.
It took just a little more work to figure out how to decode these signals so that I could track radiosonde position and altitude. For that, I use a program called Sonde Monitor. A third piece of software, called Virtual Audio Cable, pipes the demodulated FM signal from HDSDR to Sonde Monitor for decoding. So with a decent signal, it’s easy to see the geographical coordinates and altitude of a radiosonde. Sonde Monitor can also plot the position of the radiosonde on Google Maps.
If you’re wearing an orange vest, everyone assumes that whatever you are doing is legit.
To further help me find a downed radiosonde, I built a directional antenna using a handy website to design a five-element Yagi antenna for 403 MHz. I constructed it using some left-over PVC for the boom and some 1/4-inch-diameter (6-mm) copper tubing that I had in my scrap pile. Despite its origins as junk, it works great.
Weather balloons rise into the stratosphere, with their position dictated by wind movements at different altitudes. Each balloon eventually bursts, and the sonde descends by parachute. All the while, the radiosonde transmits telemetry.James Provost
Last night, I saw that the Sondehub Tracker was projecting that the 7 p.m. flight would end in Siler City, just 50 km from my home. (Readers old enough to remember “The Andy Griffith Show” might assume that this is a fictional town, but in fact it’s a real place.) So I gathered up my laptop, my antennas, and some food and water for my hunting expedition, along with one more essential piece of equipment: an orange safety vest. I didn’t really expect to be taken for a bear and shot while tromping through the woods, but in a past life I used to be a geologist. I learned then that when you pull your car over on the highway and start snooping around, people (including state troopers) tend to think you are up to no good. If you’re wearing an orange vest, however, everyone assumes that whatever you are doing is legit.
After 40 minutes’ drive, I arrived at a convenient stopping place close to the estimated landing site, which put me in the parking lot of a food-processing facility. The late-shift workers must have wondered what I was doing waving around what must have looked to them like a shrunken TV antenna. From that nearby vantage, I was able to track the radiosonde down to just 200 meters or so above ground level. I then drove 6 km to a church located close to my last position fix. And from the church parking lot, I was easily able to pick up signals from the downed radiosonde, which allowed me to map its final position on Google Maps.
Because it was dark, I headed home, but I returned today in daylight to see whether I could spot the orange parachute and perhaps even retrieve the radiosonde, which had landed just 150 meters from the road. Alas, I was thwarted by some features of the terrain not apparent from Google Maps: a chain-link fence and signs warning that trespassers would be prosecuted. So I didn’t bring home any radiosonde trophies today. But one thing worked perfectly during my outings: the orange vest. Not one person so much as asked me what the heck I was doing!
This article appears in the September 2022 print issue as “Chasing Downed Weather Balloons.”
Think back to when you were a young and an eager beginner in technology. Remember the first time you took apart your first PC, wrote your first line of code, learned how to hack Doom. The easiest way to learn technology was (and is) by being hands-on.
“Hands-on learning is 15X more effective than passive learning (ie. lectures).”
Getting started in technology can be intimidating. If you want to learn technology these days, there aren’t many great options.
Since these are purely digital, you don’t get the hands-on experience of building electronics. These often end up being just coding lessons.
Most schools don’t even offer electronics and programming in their curriculum. Even fewer engage students in hands-on learning. If you’re lucky, you might find a school that has an afterschool program led by a passionate STEM educator.
“There are nearly 500,000 open Computing jobs in the U.S. alone.”
You can find some hands-on projects that use block code and snap-on parts, but these are often oversimplified to the point that you don’t even learn the fundamentals. When you remove the potential of making mistakes, you lose the connection to how things work in the real world.
What happened to the good ole days of getting your hands dirty with real hardware and programming?
The truth is, people learn best by doing.
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Would you rather build your own bluetooth speaker, or read a textbook on electronics? Hands-on learning is not only more engaging, but fun too. Learning shouldn’t be a chore, and Creation Crate makes sure of that.
Creation Crate combines hands-on learning with educational electronics courses to teach electronics, circuits, coding, critical thinking, problem solving, and more!
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If there was ever a time to be an aspiring engineer, it’s now! The cost of components is a fraction of what it was ten years ago. Anyone can get access to the hardware and software used in everyday tech careers.
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They’ll also learn how to use components like a Breadboard, Ultrasonic Sensor, LED Matrix, 7-Segment Display, Accelerometer, Distance, Pressure, Temperature, & Humidity Sensors, LCD Screen, Keypad, Microphone Module, Resistors, Servo Motors, Motor Driver Board, and more!
Learning how to program is a tedious but rewarding process. Most engineering careers in technology require an understanding of programming languages like Java, C++, Python, Ruby, and others.
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What are Comments and Variables?
As your aspiring engineer progresses through the curriculum, they’ll learn how to build and program electronic projects that become more challenging as they learn new lessons. They’ll learn how to build things like...
A color-changing mood lamp that activates when the lights are off
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