Capacitors Made Easy The Hackaday Way

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.

Different capacitor applications. By Elcap (Own work) [CC0], via Wikimedia Commons
Different capacitor applications. By Elcap (Own work) [CC0], via Wikimedia Commons
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.

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Lint And Dog Hair Supercapacitor

[Mechanicus] has made a supercapacitor with a claimed 55 Farads per gram of active material. And he’s made it using dryer lint and dog hair. And he’s done it in 24 hours. That’s the short story. The longer story is an epic journey of self-discovery and dog ownership, and involves a cabin in the Wyoming backwoods.

So how did he do it?

He started with a home-made crucible that you maybe wouldn’t want to carry around in public as it bears more than a passing resemblance to a pipe bomb. Into that he packed his dog hair and lint, along with a generous helping of ammonia. An hour or two in a woodstove glowing red, and he’d made a rod of mostly carbon with the required high surface area. He sawed off a carbon slice, bathed it in lithium sulphate and potassium iodide electrolyte, and with the addition of a couple of pieces of stainless steel he had a supercapacitor.

Full details of his build can be found on the hackaday.io pages linked above, but there is also a handy YouTube video below the break.

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Re-Capping An Ancient Apple PSU

It sometimes comes as a shock when you look at a piece of hardware that you maybe bought new and still consider to be rather high-tech, and realise that it was made before someone in their mid-twenties was born. It’s the moment from that Waylon Jennings lyric, about looking in the mirror in total surprise, hair on your shoulders and age in your eyes. Yes, those people in their mid-twenties have never even heard of Waylon Jennings.

[Steve] at Big Mess o’Wires has a Mac IIsi from the early 1990s that wouldn’t power up. He’d already had the life-expired electrolytic capacitors replaced on the mainboard, so the chief suspect was the power supply. That miracle of technology was now pushing past a quarter century, and showing its age. In case anyone is tempted to say they don’t make ’em like they used to, [Steve]’s PSU should dispel the myth.

It’s easy as an electronic engineer writing this piece to think: So? Just open the lid, pop out the old ones and drop in the new, job done! But it’s also easy to forget that not everyone has the same experiences and opening up a mains PSU is something to approach with some trepidation if you’re not used to working with line power. [Steve] was new to mains PSUs and considered sending it to someone else, but decided he *should* be able to do it so set to work.

The Apple PSU is a switch-mode design. Ubiquitous today but still a higher-cost item in those days as you’ll know if you owned an earlier Commodore Amiga whose great big PSU box looked the same as but weighed ten times as much as its later siblings. In simple terms, the mains voltage is rectified to a high-voltage DC, chopped at a high frequency and sent through a small and lightweight ferrite-cored transformer to create the lower voltages. This means it has quite a few electrolytic capacitors, and some of them are significantly stressed with heat and voltage.

Forum posts on the same PSU identified three candidates for replacement – the high voltage smoothing capacitor and a couple of SMD capacitors on the PWM control board. We’d be tempted to say replace the lot while you have it open, but [Steve] set to work on these three. The smoothing cap was taken out with a vacuum desoldering gun, but he had some problems with the SMD caps. Using a hot air gun to remove them he managed to dislodge some of the other SMD components, resulting in the need for a significant cleanup and rework. We’d suggest next time forgoing the air gun and using a fine tip iron to melt each terminal in turn, the cap only has two and should be capable of being tipped up with a pair of pliers to separate each one.

So at the end of it all, he had a working Mac with a PSU that should be good for another twenty years. And he gained the confidence to recap mains power supplies.

If you are tempted to look inside a mains power supply you should not necessarily be put off by the fact it handles mains voltage as long as you treat it with respect. Don’t power it up while you have it open unless it is through an isolation transformer, and remember at all times that it can generate lethal voltages so be very careful and don’t touch it in any way while it is powered up. If in doubt, just don’t power it up at all while open. If you are concerned about high voltages remaining in capacitors when it is turned off, simply measure those voltages with your multimeter. If any remain, discharge them through a suitable resistor until you can no longer measure them. There is a lot for the curious hacker to learn within a switch mode PSU, why should the electronic engineers have all the fun!

This isn’t the first recapping story we’ve covered, and it will no doubt not be the last. Browse our recapping tag for more.

Magical Blinky Capacitive Sensing Tweezers

Electronic tweezers – the kind that can test the voltage between two contacts, the resistance of an SMD resistor, or the capacitance of a circuit – are very cool and very useful if somewhat expensive. We’ve seen commercial versions of these smart tweezers, hacks to make them more useful, and homebrew versions that still work very well. All of these versions are pretty large, as far as tweezers go. [kodera2t]’s version of electronic tweezers submitted for this year’s Hackaday Prize goes in the other direction: it’s the smallest set of electronic tweezers that’s still useful.

[kodera]’s electronic sensing tweezers only measure capacitors, and for good reason: chip caps usually don’t have values printed on them. These tweezers don’t print out the value of a cap on a display, either. Instead, these tweezers just flash an LED if the value of the cap is above 0.1uF. It’s simple, but surprisingly useful for most soldering jobs.

The circuit for this pair of magical tweezers is about as simple as if can get, with all the smarts contained in a very small ATtiny10. The PCB [kodera] designed is smaller than the coin cell battery, and with the help of some copper tape and possibly an insulator, this device can be mounted to any pair of tweezers. It’s a simple tool, yes, but that’s the beauty of it, and makes for a great entry into the Hackaday Prize

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Measuring Capacitors Over Their Working Voltage

Ceramic capacitors are small, they don’t leak, they’re convenient, but they are downright strange. Certain types of caps will lose their capacitance depending on the voltage they’re operating at. If you’re using ceramic caps for filters, DC to DC power supplies, bypass caps, or anything where you need an exact capacitance in a circuit, this can be a problem.

[Mathieu] has come up with a tool that’s able to measure the capacitance of a cap over its entire working range. He’s calling it the OpenCVMeter, and although the name might be slightly confusing, the functionality is not. This little box will measure the capacitance of a part over a voltage range from 1.3 to 15.5V.

By attaching the SMD tweezers or test clips to a capacitor, the OpenCVMeter ramps up the voltage and measures the capacitance of the part through the test cycle. This data is then dumped to a Chrome app – a surprisingly popular platform for test equipment apps – and a determination of the cap’s ability will to work in a circuit is displayed on the screen

If you’ve ever tooled around with antique electronic equipment, you’ll know the first thing to go bad in any piece of equipment are caps. Either caps had extremely loose manufacturing tolerances back in the day or the values really were that critical, but a dodgy cap can bring down everything from tube amps to computers. It’s a very neat tool, and something that doesn’t really exist in a single dedicated device.

The Most Powerful DIY Railgun

The US Navy is working on a few railgun projects that will eventually replace the largest guns on the fleet’s cruisers and destroyers. These rail guns will fire a projectile away from the ship at around Mach 7 on a ballistic trajectory to a target one hundred miles away. It’s an even more impressive piece of artillery than a gun with a nuclear warhead, and someday, it will be real.

most-powerful-non-military-railgunUntil then, we’ll have to settle with [Zebralemur]’s DIY mobile railgun. He built this railgun capable of firing aluminum projectiles through pumpkins, cellphones, and into car doors and blocks of ballistics gelatin.

All rail guns need a place to store energy, and in all cases this is a gigantic bank of capacitors. For this project, [Zebralemur] is using fifty-six, 400 Volt, 6000 microfarad caps. The MSRP for these caps would be about $50,000 total, but somehow – probably a surplus store – [Zebralemur] picked them up for $2,400.

These caps are just the power supply for the rail gun, and aren’t part of the structure of this already large, 250 pound gun. Luckily, with the seats down in [Zebralemur]’s car, they fit in the back of his hatchback.

These caps are charged by a bunch of 9V batteries stuck end to end. When the caps are charged, all the power is dumped into two copper bars in the gun, accelerating the aluminum projectile to speeds fast enough to kill. It’s an incredible build, but something that should not be attempted by anyone. Although this does seem to be the year that all danger seekers are busting out their electromagnetic projection flingers.

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Hackaday Links: October 18, 2015

We have our featured speakers lined up for the Hackaday Supercon, one of which is [Fran Blanche]. We’ve seen a lot of her work, from playing with pocket watches to not having the funding to build an Apollo Guidance Computer DSKY. In her spare time, she builds guitar pedals, and there’s a biopic of her in She Shreds magazine.

Halloween is coming, and that means dressing children up as pirates, fairies, characters from the latest Marvel and Disney movies, and electrolytic capacitors.

There’s a new movie on [Steve Jobs]. It’s called the Jobs S. It’s a major upgrade of the previous release, featuring a faster processor and more retinas. One more thing. Someone is trying to cash in on [Woz]’s work. This time it’s an auction for a complete Apple I that’s expected to go for $770,000 USD.

Hackaday community member [John McLear] is giving away the factory seconds of his original NFC ring (think jewelry). These still work but failed QA for small reasons and will be fun to hack around on. You pay shipping which starts at £60 for 50 rings. We’ve grabbed enough of them to include in the goody bags for the Hackaday Superconference. If you have an event coming up, getting everyone hacking on NFC is an interesting activity. If you don’t want 50+, [John] is also in the middle of a Kickstarter for an improved version.

Your 3D printed parts will rarely come out perfectly. There will always be some strings or scars from removing them from the bed. There’s a solution to these problems: use a hot air gun.

Everyone has a plumbus in their home, but how do they do it? First, they take the dinglebop, and smooth it out with a bunch of schleem. The schleem is then repurposed for later batches.