It is widely accepted that Gutenberg’s printing press revolutionized thought in Europe and transformed the Western world. Prior to the printing press, books were rare and expensive and not generally accessible. Printing made all types of written material inexpensive and plentiful. You may not think about it, but printing–or, at least, printing-like processes–revolutionized electronics just as much.
In particular, the way electronics are built and the components we use have changed a lot since the early 1900s when the vacuum tube made amplification possible. Of course, the components themselves are different. Outside of some specialty and enthusiast items, we don’t use many tubes anymore. But even more dramatic has been how we build and package devices. Just like books, the key to lowering cost and raising availability is mass production. But mass producing electronic devices wasn’t always as easy as it is today.Pre PCB
At one time, electronics were assembled by hand with point-to-point wiring and a variety of terminal strips and connections (for example, see the 1948 Motorola TV set to the right). Wires formed connections to the terminal strip (the component with five lugs near the top left), sockets, lugs on controls, and components.
This is in stark contrast to today where all the components would mount on a printed circuit board (PCB). Actually, PCBs in some form have been around since the early part of the 20th century. Even [Thomas Edison] tried to plate conductors on paper.
Despite some limited use, PCBs didn’t really take off until World War II. German mines and U. S. proximity fuses used them. Still, it would be well into the 1950s, though, before consumer electronics started to really use PCBs.
There are some technical advantages (and disadvantages) to using PCBs. But the most obvious advantage is just in labor savings. Assemblers used to use photographs and checklists to be sure they made every required connection. Not only was this labor-intensive, but it was also prone to error. The photo below shows an RCA radio factory in 1937.
Despite the name, printed circuit boards are not always printed (in fact, today, they are rarely printed). But the idea that you can make one template and automatically make tens, hundreds, or thousands of identical copies is the same idea of the printing press.Pre IC
The other printing-like process that changed electronics forever was the integrated circuit. While the PCB allowed wires to be reproduced flawlessly, the IC lets you create entire circuits with many components and then reproduce them relatively easily. There are other advantages, too (miniaturization, close matching of active devices, etc.). But the ability to produce a CPU, for example, with all its components and wiring repeatedly using a reasonably simple process has driven price and innovation in the electronics business since it became available.
If you think about it, the IC makes a lot of things practical. Let’s say you are going to create a fish finder that uses a sonic pulse to find your dinner (or the bottom of the lake). You probably need an instrumentation amplifier. How much could you spend to develop it? You probably can’t sell millions of fish finders, so you won’t have a lot of time to refine your design. It probably can’t have too many components in it either, or the price will go up and you’ll have even fewer sales.
You can buy an instrumentation amplifier as an IC very inexpensively. The company that makes it probably spent years getting it to the current state that it is in, going through multiple product iterations. Although more components do drive up the cost of an IC (due to driving up the die size), it doesn’t raise it very much, especially at smaller die sizes where manufacturing processes have very high yields. So your choice is to design your own inferior amp using a few devices at great cost or spend the buck or less to get a well-tested design with dozens of devices and great specifications. Easy choice. Of course, if you can find a highly-integrated fish finder IC (don’t laugh, the LM1812 was a thing; see page 81 of this old Popular Electronics) then you can use that and be done with your whole design in an afternoon.Better Living Through Military
The military is often the first to find ways to pay for new technology. They had been searching for a reasonable way to get more reproducible electronic assembly for some time. The U.S. Navy, for example, had project Tinkertoy. The idea was to make little modules out of ceramic with silver patterns painted on them. Components like resistors and capacitors could also be placed on the boards using automated processes. At the end, modules stacked together and little tabs around the edges served as a guide for interconnection wires as well as keys for orienting the boards.
You can see a very detailed–and a little stiff–video from 1953, below, explaining how the system worked. NIST (the technical muscle behind Tinkertoy) also has a photo gallery of both the devices and the pilot plant.Cordwood
This was an improvement, of sorts, over another technique often used in military electronics back then known as the cordwood module. Cordwood modules were the ultimate in packaging density and shock resistance when using normal components and found use in military, space, and high-speed computer systems (since the density allowed wiring to be shorter).
The idea was to use two insulating cards. Components like resistors would bridge between the two boards and nickel ribbon would form wiring on the outer surfaces of the insulating cards. Thinner cards were used where ribbons intersected. Later, single sided PCBs would sometimes act as the cards and copper traces replaced the nickel ribbons. The module in the picture below uses this method.
Of course, if a component in the middle of the module went bad, you had a lot of work to get to it.Don’t Forget the Army
The Navy wasn’t the only one thinking about this. The Army had their MM (Micro-Module) concept that looked a lot like Tinkertoy. The document covered late 1962 which was the 19th quarter of the program, so it was a little bit behind Tinkertoy. The MicroPac computer used as a test case looked pretty interesting and surprisingly compact for its day.
There were probably other module standards floating around (The NSA’s “flyball modules” come to mind), but really what everyone wanted was the integrated circuit. Then again, the first IC was in 1960, so the Micro-Module and its siblings were doomed almost from the start.Modern Times
Once in a while, you’ll still see something done in the cordwood style (like the blinking light board in the video below). The board in the video is actually sold as a kit with no instructions as a puzzle challenge. Your job is to build it without looking at instructions (like we would do that, anyway).
Of course, you still see standardized modules around. It is just usually, they take the form factor of an IC. The Basic Stamp comes to mind. You can get whole ARM systems on a little DIP board. There are still a few places where hybrid integrated circuits are used instead of pure integrated circuits.The Time Has Come
It is interesting that looking back you can see the pattern. The industry clearly wanted cheap standardized modules that didn’t require a lot of hand assembly. Just as the printing press allowed mass production of books and other reading material, PCBs allowed mass production of wiring and ICs the mass production of entire circuit “boards” with components.
There are more modern examples, too. Everyone was moving towards small boards that could run Linux when things like the Gumstix and the BeagleBone appeared. But the Raspberry Pi made it cheap and that’s what pushed high adoption rates. We are already seeing those get pushed into the chip level, too.
What you have to wonder is what trends are we in the middle of today? Will someone come out with a cheap multimaterial 3D printer (that includes metal or circuit components)? We are pushing to where the whole planet will be bathed in wireless networking, but at great cost. Will a Hackday author in the year 2110 write an article about how we used to build cell towers and satellites everywhere to get network devices connected? Spotting those trends can be lucrative or–if you fail to act on them–frustrating.
Cordwood module photo by [ArnoldReinhold] CC BY 2.5
Filed under: Hackaday Columns, History, Retrotechtacular
[Klakinoumi] wanted to use their Magsafe 1 charger from 2007 with their newer Macbook Pro Retina from 2012 — but it had a Magsafe 2 port. There were a few options on the table (buy an adapter, buy a new charger, cry) but those wouldn’t do. [Klakinoumi] went with the brute force option of grinding a Magsafe 1 charger to fit Magsafe 2.
Based on the existence of passive adapters that allow Magsafe 1 chargers to work with newer laptops, we’d assume that the older chargers are probably electrically similar to the newer models. That said, it’s not our gear and we’d definitely be checking first.
With that out of the way, it’s a simple enough modification — grind away the Magsafe 1’s magnet until it fits into a Magsafe 2 port. It really is that easy. The spring-loaded pins all seem to line up with the newer port’s pads. [Klakinoumi] reports it worked successfully in their tests with 2012, 2014 and 2015 Macbooks but that it should be attempted at your own risk — good advice, as laptops ain’t cheap.
When doing this mod, consider taking care not to overheat the connector during grinding. You could both melt plastic parts of the connector, or ruin the magnet by heating it past its Curie point.
Interested in the protocol Magsafe speaks over those little golden pins? Find out here.
Filed under: classic hacks, computer hacks, laptops hacks, macs hacks
Hackaday has been expanding into all kinds of new areas. We find ourselves stretched a bit thin and it’s time to ask for help. Want to lend a hand while making some extra dough to plow back into your projects? These are work-from-home (or wherever you like) positions and we’re looking for awesome, motivated people to help guide Hackaday forward!
Contributors are hired as private contractors and paid for each post. You should have the technical expertise to understand the projects you write about, and a passion for the wide range of topics we feature. If you’re interested, please email our jobs line, and include:
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Filed under: Hackaday Columns
From animatronic dinosaurs to [Jeff Goldblum]’s prosthetic chest hair, Jurassic Park is known for its practical effects and props. While it’s not as fancy as a breathing triceratops, YouTube’s god of resin casting has recreated one of the more endearing props from this movie. [Peter Brown] and [Pocket83] made a replica of the amber-topped cane carried by John Hammond, and it took him two years to do it.
The ‘mosquito in amber’ walking cane prop from Jurassic Park is just what you think it is – a large mosquito-looking bug trapped in 100 million year old amber. Of course, finding such a chunk of amber with the included mosquito would cost a fortune, so [Peter] turned to polyurethane resin. This block of resin was cast in two halves, with a ‘mosquito eater’ (or a crane fly) embedded in the middle. It took two years for [Peter] to cast this block of amber, but really all but two weeks of that was waiting for a few adult crane flys to appear.
With a bug encased in resin, the project went over to [Pocket83] who turned the walking cane on his lathe. There’s not much to this part of the build except for drilling a three-foot long hole down the center of a piece of wood, although the finish does make this cane look spectacular.
The long wait for crane fly breeding season was worth it. This is one of the best looking functional props from Jurassic Park. You can check out the videos for this build below.
Filed under: misc hacks
In a recent article, I lamented my distaste for carrying on the classic amateur radio conversation — calling CQ, having someone from far away or around the block call back, exchange call signs and signal reports and perhaps a few pleasantries. I think the idle chit-chat is a big turn-off to a lot of folks who would otherwise be interested in the World’s Greatest Hobby™, but thankfully there are plenty of ways for the mic-shy to get on the air. So as a public service I’d like to go over some of the many digital modes amateur radio offers as a way to avoid talking while still communicating.Of Modes and Modulations
Hams speak in terms of modes and modulations when describing their radio transmissions. The difference between the two terms is mostly not important to our discussion, though, and in practice a lot of hams use the terms interchangeably. But for completeness, modulation is a way of impressing information on a radio wave, and a mode is a way of using a modulation to communicate. Modulation schemes include amplitude modulation (AM), frequency modulation (FM), and single sideband modulation (SSB). Modes include continuous wave (CW), analog voice, digital voice, images, and data.
The digital modes I want to discuss are the ones where you can easily sit down at a keyboard and have your message appear magically on another ham’s terminal across the world. I’m not going to cover CW as a data mode here, even though it clearly was the first and is arguably the most successful digital data mode ever. International Morse Code has been going strong for 140 years, and with the many advantages of CW modulation it’s likely to remain a powerful tool for as long as people care to learn their dits and dahs. Yes, there are applications that will translate keystrokes to Morse and back, but that just feels like cheating.Equipment
Those of us with long enough memories will recall the early days of the interwebz, when dial-up connections were the only way to get online. The sound of a modem dialing Compuserve or AOL and negotiating a connection was the soundtrack of the pre-Internet days. The modem was modulating the data signals from your computer into audio tones that would fit down the analog phone line, and demodulating the returning audio signals. All ham radio data modes basically boil down to this same process — with the addition of a little outboard equipment, data from your computer is turned into audio tones that are fed to your transmitter, and audio from your receiver is decoded back into data.
In a lot of cases, the extra equipment required to tap into most data modes these days is minimal. There was a time when special converters were needed, but with a powerful DSP built into every computer sound card, pretty much any PC will do. Many ham transceivers now have sound cards built in, too, so sometimes all you need is a USB cable and the right software. FL-Digi is a popular package that supports most of the popular digital modes, provides a waterfall display that lets you easily visualize a huge swath of bands, and even controls your rig, tuning it to the selected frequency and keying the transmitter when needed.Data Modes
There is a bewildering number of data modes out there, and cruising through the HF bands at night can sound a little spooky. The warbling tones that seem to drift across the bands as the ionosphere does its nightly dance are a little eerie. The audio signature of each data mode is pretty distinctive, and experienced practitioners can pick out the mode just by the sound, or maybe with a little help from its appearance on the waterfall display. Noobs can get help with identifying the modes from any number of websites, or can rely on their software package to autodetect the mode.
Which mode to choose is largely a function of what is going to work best under the given conditions. Unlike modems connected by a telephone line, the physical medium in ham data modes is subject to a lot more potential for interference, both natural and man-made. Signals can be interrupted by crashes of static from electrical storms, two signals can arrive by different paths and suffer phasing problems, or the signal strength can be so low as to be barely above the noise floor. Any useful data mode has to take these vagaries into account, and some do a better job of dealing with one set of conditions than another.
Here’s a run-down of the major data modes you’ll run across and the relative benefits of each:RTTY
Radioteletype, or “ritty” as hams call it, is the original digital data mode. It dates back almost as far as commercial radio does, with the first RTTY service established between San Francisco and Honolulu in 1932. Then as now, RTTY uses the 5-bit Baudot code to encode each character. The simplest modulation scheme for RTTY is audio frequency-shift keying (ASFK) with a 170Hz difference between the mark and the space bits. This results in a whopping 45-baud connection (you’ll notice that most ham digital modes tend to be on the low side with regard to throughput thanks to the limited bandwidths available at the relatively low frequencies needed to take advantage of the ionospheric skip needed for long-distance contacts.) As slow as it sounds, that’s still about 60 words per minute, which is plenty fast enough to keep up with most typists.
RTTY has been joined by a raft of other data modes, but there are still RTTY aficionados out there plying the airwaves. The lower end of the 20-meter band is a good place to find RTTY operators.PSK31
One of RTTY’s advantages is that it’s technically easy to implement. But it doesn’t perform particularly well at very weak signal levels. To fix that, [Peter Martinez (G3PLX)] decided to come up with a better RTTY. In 1998, PSK31 was introduced, and it has become quite popular since then.
[Martinez] took a two-pronged approach: first, he developed a new encoding method for alphanumeric characters, called Varicode. Instead of a fixed word length like the Baudot used in RTTY, Varicode’s word-length was more Morse-like, with frequently used letters represented by shorter codes than rarer letters. Then, to modulate the code, [Martinez] leveraged the DSP in a computer’s sound card to shift the phase of an audio signal by 180° to represent a zero in the Varicode, while unshifted audio represented a logical one.
This phase-shift keying (PSK) results in a bit rate of 31 – slower than RTTY, but designed to keep up with the average typist. PSK31 is more efficient than RTTY in terms of bandwidth — only 31Hz wide — and coupled with the fact that receiver and transmitter have to be synchronized and the DSP algorithm lends itself to predicting when to expect the phase transitions that signal data being transmitted, PSK31 excels at pulling data from weak signals.Packet Modes
The user experience for RTTY and PSK31 is pretty simple — the sending party types a terse, abbreviation-rich message on a keyboard, and the receiving party reads the message on some sort of alphanumeric display. But lest you think that Amateur data modes are just for sending straight text messages like those that were sent by Model 33 teletype terminals back in the day, there are plenty of packet modes for sending more complex messages, including email.
PACTOR is a set of modes that are based on frequency-shift keying (FSK) with a 200Hz shift. Unlike RTTY and PSK31, PACTOR encodes data as 96- or 192-bit packets, which allows the use of the Automatic Repeat Request (ARQ) error control protocol to request packets that fail a CRC to be resent. PACTOR clocks in at around 200 baud.
Unfortunately, PACTOR requires an expensive piece of equipment called a terminal node controller (TNC) between the radio and the computer. To remedy this, the WINMOR protocol was developed. Similar to PACTOR in that it’s a packet mode with error correction, WINMOR does away with the TNC by using an inexpensive USB audio link, or by leveraging the sound card built into many modern transceivers.
Both WINMOR and PACTOR are gateway protocols to the Winlink 2000 network that provides email service via HF radio. Winlink is an extremely diverse hybrid network of HF and VHF radio links into internet-coupled message servers. Emails can be composed with the full-featured RMS Express client that looks and feels pretty much like any other email client. Emails can include attachments and can be sent peer-to-peer or through the network to any other Winlink user.
As useful as the Winlink network is — it has been a huge boon to emergency communications in natural and man-made disasters where local internet service is disrupted — using it is about as exciting as sending an email, because that’s exactly what you’re doing. For my money, digging a one-to-one contact out of the noise with a couple of watts on PSK31 sounds like a lot more fun. I’m glad the Winlink network is there, and it pays to practice with it from time to time, but there are a lot more challenging data modes to explore, at least in my opinion.
I’ve only scratched the surface of the digital modes available to the mic-shy ham. Here’s hoping this gets a few more new people into the hobby, or maybe even gets those licensed but largely inactive hams on the air. After all, we all need more people to not talk to.
Filed under: Engineering, Featured, radio hacks
If you’ve ever thought about having a light-up dance floor at an event, the chances are you will have been shocked at the rental cost. Doing your best impression of a young John Travolta in Saturday Night Fever doesn’t come cheap, it seems. When faced with this problem before the Furnal Equinox 2017 convention, [Av] and friends decided instead to build their own LED-lit floor.
Their design and build is shown in the video we’ve placed below the break, and though each individual light unit is straightforward it is the scale of the project and its epic build that makes it a very impressive achievement. There are 64 panels of 4 light cells, giving a total of 256 cells and 7680 RGB LEDs arranged as 2560 pixels. Each panel has a shift register PCB interfacing LEDs to the Teensy that controls the floor, and there are also microswitches talking to an Arduino Mega which provides the floor with interactivity. It’s hard to imaging this build would be possible without the people numerous who pitched in at the Toronto Hacklab for the assembly process.
The resulting 17 foot square dancefloor is a work of art, with custom programmed graphics responding to dancers moves, and even a few games along the lines of Dance Dance Revolution built in. After watching the video below, how many of you will secretly want one?
We’ve brought you quite a few dance floor projects over the years. Memorable was this one using a glass floor suspended over a swimming pool, but there has also been more than one student project floor.
Filed under: led hacks
There’s something to be said for economies of scale and few things sell more than cell phones. Maybe that’s why [NODE] took inspiration from an iPhone slide out keyboard case to create this Pi Zero W-based portable terminal. This is actually his third iteration, and in the video below he explains why he has built the new version.
By housing the custom bits in a 3D-printed frame that is size compatible with the iPhone, [NODE] manages to leverage the slick slide out keyboard cases available for the phone. The iPhone in question is an older iPhone 5, so the cases are inexpensive, compared to the latest generation. On the other hand, the iPhone 5 is recent enough that it should be hard to find a compatible case.
The circuitry itself is pretty straightforward: a battery, a charge controller, and an LCD display. The only complaint we could see was the lack of a control key on the keyboard.
Being a terminal, we would have appreciated bringing a serial port out. On the other hand, there is a full-size USB connector so you could plug in a serial cable. There’s also a micro port for charging and a small HDMI connector, which means you could use an available HDMI device as a full-size screen if you like. Although you can see a prototype, [NODE] is still refining the 3D printed parts and plans to release them soon. Having seen the prototype, you can grab the dimensions of your target phone and duplicate something similar if you’re up for a challenge.
[NODE] clearly likes portable Linux systems since we’ve seen him cobbling together slightly larger laptops before. Of course, everyone loves the Pi and that’s why we’ve also been keeping our eye on the ZeroPhone. Of course many like to play games on their phones. If you’d rather play on a real iPhone, there’s always this simple method.
Filed under: 3d Printer hacks, Cellphone Hacks, Raspberry Pi
Have you got a spare Dish Network antenna lying about? They’re not too hard to come by, either curbside on bulk waste day or perhaps even on Freecycle. If you can lay hands on one, you might want to try this fun radio telescope build.
Now, don’t expect much from [Justin]’s minimalist build. After all, you’ll be starting with a rather small dish and an LNB for the Ku band, so you won’t be doing serious radio astronomy. In fact, the BOM doesn’t include a fancy receiver – just a hacked satellite finder. The idea is to just get a reading of the relative “brightness” of a radio source without trying to demodulate the signal. To that end, the signal driving the piezo buzzer in the sat finder is fed into an Arduino through a preamp. The Arduino also controls stepper motors for the dish’s azimuth and elevation control, which lets it sweep the sky and build up a map of signal intensity. The result is a clear band of bright spots representing the geosynchronous satellites visible from [Justin]’s location in Brazil.
Modifications are definitely on the docket for [Justin], including better equipment that will allow him to image the galactic center. There may be some pointers for him in our coverage of a tiny SDR-based radio telescope, or from this custom receiver that can listen to Jupiter.
Filed under: radio hacks
We’ve seen a bunch of replacements for nixie tubes using LEDs and edge-lit acrylic for the numbers. But one of the earliest digital voltmeters used edge-lit Lucite plates for the numbers and a lot of incandescent lamps to light them up.
[stevenjohnson] has a Non-Linear Systems Model 481 digital voltmeter and he’s done a teardown of it so we can get a glimpse of the insides. Again, anyone who’s seen the modern versions of edge-lit numeric displays knows what they are: A series of clear plastic plates with numbers (or characters) etched into them, each with a light source beneath them. You turn one light on to light one plate, another to light another, and so on. The interesting bit here is the use of incandescent bulbs and the use of sequential relays to cycle through the lights. The relays make a lot of racket, especially with the case open.
[stevenjohnson] also notes that he might have made a mistake opening up the part of the machine where the plates are stored as it took him a bit to get the plates back in place and back in the unit. We’d imagine it was pretty loud if you were taking a lot of measurements with this machine, although it looks great inside and, obviously, the idea is a pretty good one. Check out this edge-lit nixie tube display or these edge-lit numeric modules.
Filed under: hardware, teardown
[Buger] had an ESP-12F and wanted to play with nodeMCU, but found they were lacking buttons for reset & flash. We’ve all been there – mucking about with a project on a breadboard, trying to save the time required to solder up a button by shorting pins with wire or bending component legs to touch. This either doesn’t work or ends up bricking the microcontroller when it inevitably goes wrong. [Buger] found a tidier solution to adding buttons to the ESP-12F with the minimum of effort.
It’s the spirit of deadbug applied to buttons. One side of a piece of wire is soldered to the pin needing to be pulled down. Component leg offcuts are ideal for this. The other end of the wire is bent up and left to float over the metal shield of the ESP-12, which is connected to ground. When you want the pin to go low, press the wire into the shield, grounding it. Let it go, and the pin returns high again, assuming your pullup resistors are all in order.
It’s a quick hack that’s much more robust than trying to hold two ends of a piece of hookup wire in place. It’s also still easier than trying to find a tactile switch solder leads to, and you don’t end up having it hanging off the board either.
For deadbug construction taken to an impressive conclusion, check out this clock built out of discrete components.
[Thanks to Richard Marko for the tip!]
Filed under: classic hacks
Nobody is likely to confuse it with the beautiful joinery that makes fine furniture so desirable. But as a practical technique, using plastic bottles as heat-shrink tubing for composite joints is pretty nifty, and the pieces produced are not without their charm.
Undertaken as an art project to show people what can be done with recycled materials, [Micaella Pedros]’ project isn’t a hack per se. She started with bottles collected around London and experimented with ways to use them in furniture. The plastic used in soda and water bottles, polyethylene terephthalate (PET), turns out to shrink quite a bit when heated. Rings cut from bottles act much like large pieces of heat-shrink tubing, but with more longitudinal shrinkage and much more rigidity. That makes for a great structural component, and [Micaella] explored several ways to leverage the material to join wood. Notches and ridges help the plastic grip smoother pieces of wood, and of course the correct size bottle needs to be used. But the joints are remarkably strong – witness the classic leaning-back-in-a-chair test in the video below.
Its aesthetic value aside, this is a good technique to file away for more practical applications. Of course, there are plenty of ways to recycle soda bottles, including turning them into cordage or even using them as light-pipes to brighten a dark room.
Thanks to [infrared411] for the tip.
Filed under: green hacks, misc hacks
Part smoothing for 3D printed parts, especially parts printed in ABS, has been around for a while. The process of exposing an ABS part to acetone vapor turns even low-resolution prints into smooth, glossy 3D renderings that are stronger than ever. The latest improvement in part smoothing for 3D printed parts is now here: use a brush. Published in Nature‘s Scientific Reports, researchers at Waseda University have improved the ABS + acetone part smoothing process with a brush.
According to the authors of the paper, traditional filament-based printing with ABS has its drawbacks. The grooves formed by each layer forms a porous surface with a poor appearance and low rigidity. This can be fixed by exposing an ABS part to acetone vapor, a process we’ve seen about a million times before. The acetone vapor smoothing process is indiscriminate, though; it smooths and over-smooths everything, and the process involves possible explosions.
The researcher’s solution is a felt tip pen-like device that selectively applies acetone to a 3D printed part. Compared to the print over-smoothed in a vat of acetone vapor, more detail is retained. Also, there’s a ready market for felt tip pens and there isn’t one for crock pots able to contain explosive vapor. This is, therefore, research that can be easily commercialized.
Filed under: 3d Printer hacks
Suppose you take a few measurements of a time-varying signal. Let’s say for concreteness that you have a microcontroller that reads some voltage 100 times per second. Collecting a bunch of data points together, you plot them out — this must surely have come from a sine wave at 35 Hz, you say. Just connect up the dots with a sine wave! It’s as plain as the nose on your face.
And then some spoil-sport comes along and draws in a version of your sine wave at -65 Hz, and then another at 135 Hz. And then more at -165 Hz and 235 Hz or -265 Hz and 335 Hz. And then an arbitrary number of potential sine waves that fit the very same data, all spaced apart at positive and negative integer multiples of your 100 Hz sampling frequency. Soon, your very pretty picture is looking a bit more complicated than you’d bargained for, and you have no idea which of these frequencies generated your data. It seems hopeless! You go home in tears.
But then you realize that this phenomenon gives you super powers — the power to resolve frequencies that are significantly higher than your sampling frequency. Just as the 235 Hz wave leaves an apparent 35 Hz waveform in the data when sampled at 100 Hz, a 237 Hz signal will look like 37 Hz. You can tell them apart even though they’re well beyond your ability to sample that fast. You’re pulling in information from beyond the Nyquist limit!
This essential ambiguity in sampling — that all frequencies offset by an integer multiple of the sampling frequency produce the same data — is called “aliasing”. And understanding aliasing is the first step toward really understanding sampling, and that’s the first step into the big wide world of digital signal processing.
Whether aliasing corrupts your pristine data or provides you with super powers hinges on your understanding of the effect, and maybe some judicious pre-sampling filtering, so let’s get some knowledge.Aliasing You say “aliasing”, I say “addition”: 35 Hz + 135 Hz, sampled at 100 Hz.
In some sense, aliasing is all in your mind. When you took your 100 Hz samples, you were probably looking for some relatively low frequency. Otherwise you would have sampled faster, right? But how is Mother Nature supposed to know which frequencies you want to measure? She just hands you the instantaneous sum of all voltage signals at all frequencies from DC to daylight, and leaves you to sort it out.
If you add together 35 Hz and 135 Hz waveforms, the resulting analog waveform will have twice the amplitude at the sampling points that correspond to 100 Hz. And when you sample, you get exactly the right value. Why did you expect otherwise?
The why is because when you think of the sampled values, you’re fooling yourself into thinking that you’ve seen the whole picture rather than just a few tiny points in time, with no data in between. But in principle, anything can be happening to the signal between samples. We just choose to use the simplest (lowest frequency) interpretation that will fit.
Not only does this seem reasonable, but this is also deeply ingrained in human physiology, so there’s no use fighting it. When you watch a Western, and the stagecoach accelerates so that the spokes in its wheels just match the film’s frame rate, you see the wheels as stopped because each frame was taken when the next spoke was in the same position as in the previous frame. As it speeds up further, you even think you see the wheel turning backwards. The illusion that sampled data comes from the “obvious” underlying signal is strong.
So if sampling adds together signals from different frequencies, how can we disentangle them? The short answer is that once the data has been collected, you can’t. There’s just not enough information there to recreate the full bandwidth of the universe.
But we can avoid aliasing when it’s a problem. The brute force method is to simply take more frequent samples. Since the alias frequencies are the desired frequency plus or minus integer multiples of the sampling frequency, , sampling faster pushes away the frequencies that would otherwise mess up your data. If you could see between the data points in the various graphs, you could tell that not all of the signal was actually coming from 35 Hz.
Indeed, if you knew beforehand that your 35 Hz signal was contaminated with a 135 Hz signal, you could sample at 120 Hz, resulting in first-order aliases at -115 Hz and 15 Hz. Now you could separate the signals from each other using fancy DSP tricks. Of course, if the signal also has nuisance signals at 155 Hz, this won’t work.Anti-Aliasing
An alternative is to get rid of the would-be aliases before sampling in the first place. When you wake up in the morning, and look outside to see the sun rise, you don’t ask yourself if you’ve slept for one night or two. That’s because it’s impossible that you’ve slept for 32 hours without noticing, right? Similarly, to anti-alias your data before sampling, you just need to rule out the higher multiples of the sampling frequency with a filter.From Lyons’ “Understanding Digital Signal Processing”, with Lowpass Filter Profile Added
Lowpass sampling is the name for this procedure of applying a lowpass filter to your data before sampling it. Filtering out the high frequency content before sampling means that there’s nothing there to alias down, and the lowest frequencies, which you’re going to perceive as being “the sample” anyway, are the only ones present. This is done in nearly every analog-to-digital converter one way or another.
Because the negative frequencies interfere with our desired signal, the cutoff frequency of the filter needs to be set at 1/2 of the sampling frequency, or at the top of the desired bandwidth, whichever’s lower. When recording CDs, for instance, they are passed through a steep 20-22 Khz cutoff filter before being sampled at 44.1 kHz. A potentially contaminating 30.1 kHz signal, which would alias down to -14 kHz after sampling, is simply filtered away before it ever hits the ADC.
When you sample using an ADC, consider what’s going on at multiples of the sampling frequency. Do you need a lowpass filter? We suspect you might.Bandpass Sampling
Finally, here is the super-power side of aliasing. Just as you can count the number of spokes on the “stopped” wagon wheel in Stagecoach, you can also get information about frequencies that are higher than the sampling rate by taking advantage of aliasing. And just as with the spokes on the wheel, even though it looks like you’re drawing samples from a single period of the waveform, you’re actually getting snapshots of different phase positions from across many periods of the wave. But if the desired signal is relatively consistent — the wagon’s spokes are roughly interchangeable — it won’t matter.
Bandpass Sampling (or undersampling) is the DSP name for this super power. You know that signals at all multiples of the sampling frequency are all going to get mixed together when you sample. The trick is just the same as in the lowpass case: simply filter out all the frequency bands except for the one that you want, and let aliasing do the frequency downconversion for you.
So if we were interested in capturing the 135 Hz wave, we would simply filter as tightly around the desired 135 Hz as we can, sample at 100 Hz, and read the resulting frequency off at 35 Hz. Note that the ADC you use still has to be able to resolve the 135 Hz signal — if its input is too sluggish, it will smear out the high-frequency content, leaving you with a mess. (The exposure on the movie camera has to be fast enough to “freeze” the wagon wheel as well. Garbage in, garbage out.) Still, you can get the same information about the 135 Hz signal using only 100 samples per second instead of 270 by using this trick if your ADC is up to it.More on Aliasing
There’s actually a lot more to aliasing than we have room to cover here, mostly because it informs all aspects of sampling, and thus DSP. If you want to get in deeper, any good DSP textbook should do. I really liked [Richard Lyons]’s “Understanding Digital Signal Processing”. (Here is the chapter on bandpass sampling for your enjoyment.)
If you’re a little bit uneasy with all of the “negative frequency” stuff above, it actually makes a lot more sense when viewed in the complex plane and with I/Q sampling. For a gentle video introduction to both complex signals and sampling theory, I like [Michael Ossmann]’s video series on software defined radio basics. Watch at least Chapter Six on complex numbers and then Chapter Nine on aliasing. If you don’t have any interest in SDR applications and you’re already comfortable with complex signals, you can actually get by starting Chapter Nine at 14:00 and going through 24:00. It’ll be the best ten minutes that you’ve spent. (Other than the ten reading this article, naturally.)
If you’re wondering just how those signals get sampled in the first place, try [Bil Herd]’s roundup of ADC techniques.
Filed under: Engineering, Featured, how-to
The audio cassette is an audio format that presented a variety of engineering challenges during its tenure. One of the biggest at the time was that listeners had to physically remove the cassette and flip it over to listen to the full recording. Over the years, manufacturers developed a variety of “auto-reverse” systems that allowed a cassette deck to play a full tape without user intervention. This video covers how Akai did it – the hard way.
Towards the end of the cassette era, most manufacturers had decided on a relatively simple system of having the head assembly rotate while reversing the motor direction. Many years prior to this, however, Akai’s system involved a shuttle which carried the tape up to a rotating arm that flipped the cassette, before shuttling it back down and reinserting it into the deck.
Even a regular cassette player has an astounding level of complexity using simple electromechanical components — the humble cassette precedes the widespread introduction of integrated circuits, so things were done with motors, cams, levers, and switches instead. This device takes it to another level, and [Techmoan] does a great job of showing it in close-up detail. This is certainly a formidable design from an era that’s beginning to fade into history.
The video (found after the break) also does a great job of showing glimpses of other creative auto-reverse solutions — including one from Phillips that appears to rely on bouncing tapes through something vaguely resembling a playground slide. We’d love to see that one in action, too.
One thing you should never do with a cassette deck like this is use it with a cassette audio adapter like this one.
Filed under: digital audio hacks, teardown
On Saturday the Hackaday community turned out in force to try something new. The first Hackaday Unconference was held in three places at the same time, and I was in Chicago and was amazed at the turnout and variety of presentations. The image above sums up the concept quite well, everyone shows up ready to give an eight minute talk, but as a whole, no one knows what to expect. Well, we should have known to expect awesome and that’s what we got.
As usual, people are excellent… to one another and in adapting to the fluid nature of the day. Pumping Station: One, a renowned Hackerspace in the Avondale neighborhood near downtown Chicago, opened their doors for us. Not knowing how many people to expect we set up two presentation rooms with a third on deck just in case it was needed.
We just barely squeezed everyone in one room for the first track but ended up splitting into two for part of the day. Here you can see that second room filling up. Even so we still had a handful of presentations that didn’t get a chance to shine — we simply must do this again so they can have the chance and because I had such a great time!Cherry Picking Talks
It’s really tough to report on all of these talks. Some people came with prepared talks including slides and props. Many came with talk topic and structure in mind and gave their talk adapted to some of the others they had heard that day. Even those who didn’t plan to speak were easily cajoled into giving us two minutes on what projects they’re exploring these days.
Many of our readers who couldn’t be there asked us to record it, but we didn’t want the presence of cameras to dampen anyone’s spontaneity, so we left them off. Here’s some of the highlights I remember from Saturday.
[Cameron Blocker] has been experimenting with graphics cards, using the GPU and abusing the VGA outputs as signal generators. After all, a VGA video card is just three fast DACs outputting specific signals on a very strict timing scheme.
When someone says “$50 Thermal Camera” the next word out of your mouth should be “impossible”. Or so I thought. [Michael Shaub] was at the Uncon to prove me wrong in a big way. He hit up everyone’s favorite mixed-bag of tools (Harbor Freight) for a non-contact thermometer. He put it on a two-servo gimbal and then followed the software rabbit hole to stitch together heat-map overlays onto a still image. This is really excellent work and we’re trying to compel him to post more details so make sure to like and follow his project. It takes some time to scan in an entire image, but if you’re looking for poorly insulated areas of your home what’s the rush? This is fun to build and will work great for that purpose.
I greatly enjoyed [Bob Baddeley’s] talk on design considerations when you want to manufacture in plastics. This was huge expansion on the peek we got with his Injection Molding article. But the talk included a range of manufacturing processes, starting with differences between thermoset and thermoplastics and walking through ever avenue extending outward.
[Chris Gammell] has recently adopted a new design for a standard expansion header on his electronic designs. These are electronics used to teach design and layout skills in his Contextual Electronics courses and so the header is called the CE Header. Having presented to the room it was interesting to hear the discussion on good and bad choices (should the serial pins be on opposite sides of a dual row header or does that complicate addon routing, etc.)
A couple of weeks ago I heard on the radio that the average age of farmers in Wisconsin is now 60 years old. (I live in Wisconsin if that helps the story make more sense). This is alarming to me as I know that Japan is seeing something of a crisis with the rising age of their farming population. I’ve been reading and researching about the issue and gave my talk on some of the promising hardware advances to help these farmers, and some of the social issues that need to be solved to help get more new blood interested in feeding the world.
Would it be a Hackaday event without some hands-on Hardware? [Will Caruana] is trying to build a reliable single-cell injector for biohacking (and also more traditional lab work of course) at a greatly reduced rate. One method he’s using is a blowtorch and glass pipette. Of course Pumping Station: One has a hot metal workshop and one of the members happily brought his blowtorch over for the demo. Very cool… er… hot, very very hot.
There were even a few talks on products pushing toward a launch. [Adam] and [Will] came down from Milwaukee to show off the MagneTag rig they’ve been building. It’s a chest and back plate that you strap on, then have a fight with foam swords. Scoring is automatic (seen on the screen behind them) and there was an engineering challenge that went into detecting hits on the shields but not elsewhere. Get this, they have the swords encased in foam by the same company that makes the cheeseheads.
[Andrew] was showing off some of the videos his made with his robot arm Evezor. The belt and servo driven arm looks pretty incredible and he loaded up the plotter tool and had the bot write us this letter.Learning and Curiosity as Lifestyle
What makes an Unconference so special is that it’s about sharing excitement about learning. This means listening to what other people are working on, and spending time thinking about something that you might not otherwise have been exposed to. This is incredibly important and it’s what The Hackaday Prize is all about. That makes these Unconferences a great event to happen a few days before we launched this year’s challenge.
One of the final talks in Chicago was a talk by [Dan White] about why we learn so much outside of school. The gist of the discussion is to explore who we can “learn by doing” in a school setting more than we already do. But for me, I’ve made it my mission in life since I left school to learn in my free time. That’s what Hackaday’s all about and I don’t think I would have made it this far with electronics and fabrication without the inspiration I’ve drawn from Hackaday over the years.
We have the power to inspire and this is why we host the Hackaday Prize every year. Every single entry has the power to change the world. Maybe not directly, but the pollination of knowledge, the infection of excitement, and the power of inspiration. Build something that helps you strengthen your skills and your knowledge, but this time, also think about how to fix a problem, to inspire someone coming up behind you trying to learn their own hardware skills. It’s a way to give back for all the people and projects that helped you get here.Quick Thank Yous Dinner (and breaks) were a flurry of conversations and demos.
We already thanked Pumping Station: One for hosting. Their officers and members pitched in to help with staffing, organization, preparation, and cleanup. Thank you! Digikey, Microchip, and Supplyframe are our awesome sponsors for the 2017 Hackaday Prize and provided financial support for this event. We had a bounty of wonderful food, swag, and giveaways because of that. It turns out hackers like bananas 2:1 over clementines, toasted sandwiches are a huge hit, and everyone loves local craft beer although they will make fun of you for carding people at the keg.
Thank you all for attending. I hope to make Hackaday Unconferences a regular thing all over the world. Feel free to pester us to come to your Hackerspace for one, but you don’t have to wait for us. If you interested in hosting a live event we’ll help you get started, just let us know.The HackadayPrize2017 is Sponsored by:
Filed under: cons, Hackaday Columns, The Hackaday Prize
[Michal Zalewski] has radiation on the brain. Why else would he gut a perfectly-horrible floor lamp, rebuild the entire thing with high-power RGB LEDs, and then drive it with a microcontroller that is connected up to a Geiger-Müller tube? Oh right, because it also looks very cool, and Geiger tubes are awesome.
If you’ve been putting off your own Geiger tube project, and we know you have, [Michal]’s detailed explanation of the driver circuit and building one from scratch should help get you off the couch. Since a Geiger tube needs 400 volts DC, some precautions are necessary here, and [Michal] builds a relatively safe inverter and also details a relatively safe way to test it.
The result is a nice piece of decor that simultaneously warns you of a nuclear disaster by flashing lights like crazy, or (hopefully) just makes a nice conversation piece. This is one of the cooler Geiger tube hacks we’ve seen since [Robert Hart] connected up eighteen Geiger tubes, and used them to detect the direction of incoming cosmic rays and use that to compose random music (YouTube, embedded below).
Filed under: misc hacks
[agp.cooper]’s son recently went to China, and the biggest complaint was the Great Firewall of China. A VPN is a viable option to get around the Great Firewall of China, but [agp] had a better idea: an acoustic coupler for his son’s iPhone.
Hackaday readers of a recent vintage might remember an old US Robotics modem that plugged into your computer and phone line, allowing you to access MySpace or Geocities. Yes, if someone picked up the phone, your connection would drop. Those of us with just a little more experience under our belts will remember the acoustic coupler modem — a cradle that held a phone handset that connected your computer (indirectly) to the phone line.
With a little bit of CNC work, [agp] quickly routed out a block of plywood that cradled his son’s iPhone. Add in a speaker and a microphone, and that’s an acoustic coupler. There’s not much to it, really. The real challenge is building a modem.
In the late 90s, there were dedicated chipsets for modems, and before that, there was a 74xx-series chip that was a 300-baud modem. [agp] isn’t using anything like that. He’s building a modem with an Arduino. This is a Bell 103A-compatible modem, allowing an iPhone to talk to a remote computer at 300 bits per second. This is a difficult challenge; we’re not able to get 33kbps over a smartphone voice connection simply because of the codecs used. However, with a little bit of work, [agp] managed to build a real modem with an Arduino.
Filed under: Arduino Hacks
Back in the day, building a DIY radio was fun! We only had to get our hands at a germanium diode, make some coils, and with a resistor and long wire as an antenna maybe we could get some sound out of those old white earplugs. That was back then. Now we have things like the Si4703 FM tuner chip that can tune in FM radio in the 76–108 MHz range, comes with integrated AGC and AFC, controlled by I2C, as well as a bunch of other acronyms which seem to make the whole DIY radio-building process outdated. The challenges of the past resulted in the proven solutions of the present in which we build upon.
This little project by [Patrick Müller] is a modern radio DIY tutorial. With an Arduino Nano as the brains and controller for an Si4703 breakout board, he builds a completely functional and portable FM radio. A small OLED display lets the user see audio volume, frequency, selected station and still has space left to show the current available battery voltage. It has volume control, radio station seek, and four buttons that allows quick access to memorized stations. The source code shows how it is possible to control the Si4703 FM tuner chip to suit your needs.
As for ICs, not everything is new, [Patrick] still used the good old LM386 amp to drive the speaker, which is almost 35 years old by now. As we can listen in the demo video, it can still output some seriously loud music sounds!
Sadly, due to the FM receiver band constraints, you can’t listen to Jupiter on this one.
Filed under: Arduino Hacks
Clocks that read time via received radio signals have several advantages over their Internet-connected, NTP-synchronised brethren. The radio signal is ubiquitous and available over a fairly large footprint extending to thousands of kilometres from the transmitting antennae. This allows such clocks to work reliably in areas where there is no Internet service. And compared to GPS clocks, their front-end electronics and antenna requirements are much simpler. [Erik de Ruiter]’s DCF77 Analyzer/Clock is synchronised to the German DCF77 radio signal, which is derived from the atomic clocks at PTB headquarters. It features a ton of bells and whistles, while still being simple to build. It’s a slick piece of German hacker engineering that leaves us amazed.
Among the clock functions, it shows time, day of the week, date, CET/CEST modes, leap year indications and week numbers. The last is not part of the DCF77 protocol but is calculated via software. The DCF77 analyzer part has all of the useful information gleaned from the radio signals. There are displays for time period, pulse width, a bit counter, bit value indicator (0/1) and an error counter. There are two rings of 59 LEDs each that provide additional information about the DCF77 signal. A PIR sensor on the front panel helps put the clock in power save mode. Finally, there is a whole bunch of indicator LEDs and a bank of switches to control the various functions. On the rear panel, there are RJ45 sockets for the DCF77 receiver antenna board, temperature sensor and FTDI serial, a bunch of audio sound board controls, reset switches and a mode control switch.
His build starts with the design and layout of the enclosure. The front panel layout had to go through a couple of iterations before he was satisfied with the result. The final version was made from aluminium-coated sandwich-panel. He used an online service to photo-etch the markings, and then a milling machine to carve out the various windows and mounting holes. The rear panel is a tinted acrylic with laser engraving, which makes the neatly laid out innards visible for viewers to appreciate. The wooden frame is made from 40-year-old Mahogany, sourced from an old family heirloom desk. All of this hard work results in a really professional looking product.
The electronics are mostly off the shelf modules, except for the custom built LED driver boards. The heart of the device is an Arduino Mega because of the large number of outputs it provides. There are seven LED driver boards based around the Maxim 7221 (PDF) serial interface LED drivers – two to drive the inner and outer ring LEDs, and the others for the various seven-segment displays. The numerous annunciator LEDs are driven directly from the Arduino Mega. His build really comes together by incorporating a noise resilient DCF77 decoder library by [Udo Klein] which is running on a separate Arduino Uno. All of his design source files are posted on his GitHub repository and he hopes to publish an Instructable soon for those who would like to build one of their own.
In the first video below, he walks through the various functions of the clock, and in the second one, gives us a peek in to its inside. Watch, and be amazed.
Thanks for the tip, [Nick]
Filed under: clock hacks
Bees are a crucial part of the ecosystem – without bees to act as pollinators, many plant species wouldn’t be able to reproduce at all! It’s unfortunate then that bees are struggling to survive in many parts of the world. However, [Louise Cosgrove] is doing her part – building homes for bees in old television sets.
The project started when Louise’s son-in-law left 100 (!) analog TVs at her home, having already recycled the picture tubes. That sounds kind of impolite to us, but we’ll give them the benefit of the doubt and assume they had some sort of agreement. [Louise] realised the empty television cases had plenty of ventilation and would make ideal homes for bees. By filling the empty boxes with natural materials like wood, bamboo and bark, it creates nesting places that the bees can use to lay their eggs.
We’ve seen bees on Hackaday beefore (tee-hee) – like this beehive wired for remote monitoring.
[Thanks to Stuart Longland for the tip!]
Filed under: green hacks