If you build electronic circuits on a regular basis the chances are you will have used capacitors many times. They are a standard component along with the resistor whose values are lifted off the shelf without a second thought. We use them for power supply smoothing and decoupling, DC blocking, timing circuits, and many more applications.
A capacitor though is not simply a blob with two wires emerging from it and a couple of parameters: working voltage and capacitance. There is a huge array of capacitor technologies and materials with different properties. And while almost any capacitor with the right value can do the job in most cases, you’ll find that knowing more about these different devices can help you make something that doesn’t just do the job, but does the best possible job. If you’ve ever had to chase a thermal stability problem or seek out the source of those extra dBs of noise for example you will appreciate this.
If you are a novice electronic constructor, you will become familiar with common electronic components. Resistors, capacitors, transistors, diodes, LEDs, integrated circuits. These are the fodder for countless learning projects, and will light up the breadboards of many a Raspberry Pi or Arduino owner.
There is a glaring omission in that list, the inductor. True, it’s not a component with much application in simple analogue or logic circuits, and it’s also a bit more expensive than other passive components. But this omission creates a knowledge gap with respect to inductors, a tendency for their use to be thought of as something of a black art, and a trepidation surrounding their use in kits and projects.
We think this is a shame, so here follows an introduction to inductors for the inductor novice, an attempt to demystify them and encourage you to look at them afresh if you have always steered clear of them.
As a fresh-faced electronic engineering student while the first Gulf War was raging in a far-off desert, I learned my way through the different families of 74 logic at a university in the North of England. 74LS was the one to use, the story went, because it’s quick and doesn’t use much power. At the time, there was an upstart on the scene: 74HC. Now that’s really quick. New. Exotic, even.
Thus an association was formed, when you want a quick logic function then 74HC is the modern one to go for. It could have been a lifelong love affair, but over twenty years, after many factors of speed increases and some RF tricks with gates we wouldn’t have dreamed of back then, it’s over. There is a whole world of newer logic families to choose from, and while HC is still good at what it does, it’s well past time to admit that it may just have been superseded.
A tendency to cling to the past with logic families is pretty harmless. Like [Adam Fabio]’s TIP power transistors they’re pretty cheap, still very much in production, and still do most jobs demanded of them excellently. But what prompted this piece was a far more egregious example of an old component still being specified: the RCA 40673 dual-gate MOSFET. Launched in the mists of time when dinosaurs probably still roamed the earth, this static-sensitive four-pin TO72 found a home in a huge variety of RF amplifiers, oscillators, and mixers. It worked well, but as you might expect better devices came along, and the 40673 was withdrawn some time in the 1980s.
Unfortunately, nobody seems to have told a section of the amateur radio community about the 40673’s demise. Or perhaps nobody’s told them that many scrap analogue TV tuners of a certain age will yield a perfectly good newer replacement for free. Because even today, thirty years after the 40673 shuffled off this mortal coil, you can still find people specifying it. If you have a stash of them in your junk box, they’re worth a small fortune, and yours could be the bench with the throng of people at the next ham radio convention.
A different but equally annoying manifestation of the phenomenon comes when the device everyone likes to specify is not very old and very much still in production, but the designer hasn’t taken the time required to check for a cheaper alternative. Nobody ever got fired for buying IBM, they say, but perhaps they should be fired for specifying an AD8307 logarithmic amplifier in an amateur radio power meter. Don’t take this the wrong way, it’s a beautiful chip and probably a lot of work at Analog Devices has gone into laser-trimming resistors to make it perform to an extremely demanding specification. But eleven dollars for a chip? When a cursory search will turn up Maxim’s MAX9933 which does a perfectly good job in this application at well under two dollars? Someone isn’t doing their homework.
Sometimes there are components for which there are no perfect replacements. Germanium point-contact diodes, for example. 1N34As and OA91s are becoming like hen’s teeth these days, and though Schottky diodes can replace them in many applications, there are still a few places if you’re a radio person you’ll hanker for the original. There are suppliers on Alibaba who claim to manufacture 1N34s, but the pictures always look suspiciously like 1N4148s, and anyway who can find a home for a hundred thousand diodes? (Hang on, this is Hackaday. There will be someone out there with a hundred-thousand-diode project, you can count on it.)
OK, maybe germanium diodes are an edge case and the examples above have a radio flavour, but you get the picture. What the full-blown rant in the previous paragraphs has been building up to is this: a plea for designers to do their homework. Please try to design every project for the next two decades, and as though any extras in the component price come from your company’s bottom line. (We’ll make exceptions for building something for which the whole point is a retro circuit. An Apple I replica like the Mimeo 1 needs old logic chips for artistic purposes.)
Is there a vital electronic engineering skill that’s being lost here perhaps? Back when the Internet was the sole preserve of boffins and Tim Berners-Lee hadn’t yet plugged his hypertext ideas into it, we relied on catalogs. Big paper-bound books the size of telephone directories were our only window into the exciting world of electronic components. If you’re an American yours was probably from Radio Shack, but for most UK-based hackers and makers who couldn’t get their hands on a commercial account from RS or Farnell that meant the Maplin catalogue. Before they moved in a consumer-electronics direction, they were a component specialist whose catalogue with its distinctive spaceships on the cover could be bought at large newsstands.
It’s difficult to describe the impact of electronics catalogues in the ’70s and ’80s to someone who has known only the abundance of information from the WWW. These publications were our only window into the world of electronic components. They contained significant excerpts from semiconductor data sheets, and we read their wealth of information from cover to cover. We knew by heart what each device was capable of, and we eagerly devoured each new tidbit of information as it arrived.
In short, when we specified a component, we did so with a pretty good knowledge of all the components that were available to us.
By comparison, nowadays we can quickly buy almost any device or component in production from a multitude of suppliers. There are millions more devices available, and if RS or Farnell don’t have the part then Mouser or Digi-Key are sure to provide. The WWW allows us to find what we need in short order, and the miracle of global distribution means that we can have it delivered within 48 hours almost wherever we live.
Which means that all the new devices are available to us, but we’ve lost the ability to keep on top of them. We’ve become information rich, but knowledge poor. Printed catalogs still exist, but the sheer volume of information they contain forces brevity upon their entries and expands the size of the publication to the point at which it becomes an unwieldy work of reference. We therefore tend to stick with the devices and components we know, regardless of their cost or of whether they have been superseded, and our work is poorer for it.
We need to relearn the skill of inquisitiveness when it comes to the parts we use, and to rediscover the joy of just browsing, even if the medium is now a huge suppliers’ web site rather than a paper catalog. Otherwise we’ll still be looking at circuit diagrams containing 74LS logic and 40673 MOSFETs in the 2030s, and that can’t be a good thing!
There is of course also a slightly macabre alternative scenario. The highest online price we found for 40673s was over $30 each, so if a producer can make that kind of silly money then there’s a danger that RCA’s successors will see a business model in exhuming the corpse and re-animating it, thus ensuring that we’ll never be free of the undead. We need to make sure that doesn’t happen!
The fact that you’re reading Hackaday puts you into one of three categories: you wish you had a lot more tools, you’re on the way to a well-stocked workshop, or you’re trying to pass on your shop surplus to someone who will love it like you do. There’s now a perfect solution for the buy-upgrade-horde cycle we all inevitably fall into: the Tindie Flea Market. If you use something to make hardware, this is going to be the place to buy or sell it.
Has that starter scope been collecting dust since you picked up not one, but two better models? We know you can’t part with it unless you know it’s not going to be thrown out, and this is the chance to find not just a good home, but an owner that will use and cherish it. This goes for all kinds of great tools. After all, how do you find someone to take that pick and place off of your hands?
At launch, the Tindie Flea Market categories will include Adapters and Cables, Audio and Video, Batteries and Power, Bulk Components, Equipment, Fasteners, RC, and Small Tools. Maybe I’ll finally be able to find a home for that tube of power transistors I ordered years ago in the wrong package — and maybe even that long tape of EEPROM that I ordered in 1.8v instead of 3.3v. Time to start my listings and keep good stuff out of the landfill. Yet another great reason we were so happy to welcome Tindie to the Hackaday family.
Laying out one PCB, sending it out to a fab, stuffing it with components, and having the whole thing actually work when you’re done is a solved problem. Doing the same thing and having it plug in to another PCB… well, that’s a bit harder. Forget about building a PCB and having it fit inside an enclosure the first time.
The usual solution to this problem is printing the board to be fabbed on a piece of paper, take some calipers, and measure very, very carefully. Extra points for sticking a few components you’re worried about to the paper before lining the mechanical prototype up to the existing board. [N8VI] over at the i3 Detroit hackerspace had a better idea – print the whole thing out on a 3D printer.
[N8VI] is working on a software defined radio cape for a BeagleBone. He was a bit concerned about a few caps getting in the way of a board stack. This was tested by printing out a bit of plastic in the shape of the new board, adding header spacers and parts that might be troublesome.
While the idea is great, there’s not much in the way of a software solution or a toolchain to make plastic copies of completed boards. We know rendering 3D objects from KiCAD is rather easy, but there aren’t many tools available for those of us who are still stuck with Eagle. If you know of a way to print populated boards, drop a note in the comments.
Online parts search and ordering is a godsend compared to the paper-catalog days of yore. This is fact, there is no argument otherwise (despite [Dave Jones’] assertion that sourcing connectors is so much simpler if you have pages full of images). Just being able to search was a game changer. But how far do you think the concept has come since the transition online? [Chris Gammell] plans to spark a leap forward with Parts.io, an electronic component info delivery system that spans both manufacturers and distributors.
So what’s wrong with what we’re doing now? Nothing… unless you hate wasting time. Sourcing parts is time consuming. Certainly the parametric search on distributors’ sites like Mouser and Digikey have improved. Plus we’ve seen hacks that do things like automatically pull in stock data to a spreadsheet. But the real issue isn’t figuring out how to buy stuff, it’s figuring out what to use in a design. Surely there is opportunity for improvement.
Parts.io has its sights set on a better path to part discovery. Yes, this is parametric search but it will return data for all parts from all manufacturers. The distinction may not be completely obvious, but for example if you are searching on Element14 you’re only getting data on the parts that Element14 carries. Once you have drilled down to a reasonably manageable pool of components you get what you would expect: one-click datasheets and a roundup of pricing and availability from worldwide distributors. The presentation of the parts is grouped into families that differ in trailing parts designators, and I must say I am impressed at the interface’s ability to roll with you. It feels easier to find alternative parts after the drilldown where in my past searches I would have started completely over again.
The service started in private alpha in October but is now available for public use. You can search for a part without logging in, but a few features have been held back for those that sign up for a free account. Most notably this includes the ability to upload your BOM, add parts as favorites, and access their forums.
Is this a game changer? That’s for you to decide. You can give it a try yourself or watch [Chris’] feature walkthrough video found after the break.
[Al] recently returned from a trip to China. While there he toured some of the component markets in Shenzhen, the electronics assembly epicenter of the world. While he doesn’t focus too closely on what is actually being sold there, we found his description of the markets themselves and other notable attractions around the area quite interesting.
Shenzhen is different from some of the other component wonderlands we’ve heard about ([Ian Lesnet’s] tour of Akihabara in Japan comes to mind). First of all it may be a bit more difficult to get there. US Citizens need a Visa to enter China, and must fly to Hong Kong and take a ferry to the mainland. [Al] reports that the traffic is horrendous and rush-hour can turn a ten mile ride that usually takes ninety minutes into a three hour tour… a three hour tour!
The side affect of the market being out of the way is that the prices aren’t as inflated as they may be in more geek-tourist-friendly locations. That being said it also sounds like the vendors are interested in selling you a few thousand units rather than a single component. Follow the link at the top for the market tour, a stop at Seeed Studios (who will apparently sell you a map of the best markets to visit), and the rest of the attractions that [Al] encountered.