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ถูกปรับปรุง 4 hours 18 min ก่อน

Thermoelectric Paint Opens Prospect Of Easier Energy Harvesting

6 hours 38 minก่อน

We will all be used to the thermoelectric effect in our electronic devices. The property of a junction of dissimilar conductors to either generate electricity from a difference in temperature (the Seebeck effect), or heating or cooling the junction (the Peltier effect). Every time we use a thermocouple or one of those mini beer fridges, we’re taking advantage of it.

Practical commercial thermoelectric arrays take the form of a grid of semiconductor junctions wired in series, with a cold side and a hot side. For a Peltier array the cold side drops in temperature and the hot side rises in response to applied electric current, while for a Seebeck array a current is generated in response to temperature difference between the two sides. They have several disadvantages though; they are not cheap, they are of a limited size, they can only be attached to flat surfaces, and they are only as good as their thermal bond can be made.

Researchers in Korea have produced an interesting development in this field that may offer significant improvements over the modules, they have published a paper describing a thermoelectric compound which can be painted on to a surface. The paint contains particles of bismuth telluride (Bi2Te3), and an energy density of up to 4mW per square centimetre is claimed.

This all sounds impressive, however as always there is a snag. The coating is painted on, but then it must be sintered at high temperature to form the final material. Then since the thermoelectric Seebeck effect voltage generated across a junction is tiny, some means must be arrived at to connect multiple regions of paint in series to achieve a usable voltage. The paint is produced in both n- and p-type semiconductor variants, so they appear to achieve this series connection by alternating bands of each. And finally the efficiency of the whole is only as good as the ability of its cold side to lose heat, so we are guessing to be effective it would require something extra to improve heat transfer away from it. Still, it will have a thermal bond with its substrate that is second to none and it has the potential to cover the entire surface of a hot item, so it shows considerable promise. The researchers discuss using it for power generation, but  we wonder whether there is also a prospect of it being used as a Peltier effect device to provide enhanced cooling.

We’ve covered many conventional thermoelectric generators in the past. The smallest was probably this LED ring, but we’ve also shown you a thermoelectric charger for use in rural Mongolia, and this very neat candle-powered fan.

Thanks to [Jack Laidlaw].


Filed under: chemistry hacks, green hacks

A Handy Tutorial For Voice-Command Awesomeness

9 hours 38 minก่อน

When somebody can’t find a guide on how to accomplish a particular task, we here at Hackaday admire those individuals who take it upon themselves to write one for the benefit of others. Instructables user [PatrickD126] couldn’t find a write-up on how to connect Amazon’s Alexa service, and Echo to his Raspberry Pi home security system, so his handy tutorial should get you up to speed for your own projects.

[PatrickD126] shows how loading some software onto the Raspberry Pi is readily accomplished along with enabling Alexa to communicate more directly with the Pi. From there, it’s a matter of configuring your Amazon Web Services account with your preferred voice commands, as well as which GPIO pins you’d like to access. Done! [PatrickD126] notes that the instructions in the guide only result in a temporary solution, but suggests alternatives that would allow your project to operate long-term.

For more advanced users this tutorial is probably rote, but it could save time in a crunch or hackathon scenario. Now all you have to do is connect this project to a typewriter that will allow you to dictate your next report — old school style.

[Thanks for the submission, Patrick D!]


Filed under: Raspberry Pi

LEGO Strain Wave Gear is Easy on the Eyes

12 hours 38 minก่อน

We are continually amazed by the things people do with LEGO and Technics, especially those that require incredible engineering skill. There’s an entire community based around building Great Ball Contraptions, which are LEGO Rube Goldberg machines that move tiny basketballs and soccer balls from one place to another. Except for a few rules about the input and output, the GBC horizons are boundless.

Famed GBC creator [Akiyuki] recently built a GBC module that’s designed to show the movement of strain wave gear systems. These types of gear systems are used in industrial applications where precision is vital. Strain wave gears are capable of reducing gear ratios in a small footprint.

There are three parts to a strain wave gear: the wave generator, the flex spline, and the circular spline. [Akiyuki]’s wave generator is the elliptical gray disk in the center. It is attached to the input shaft. The flex spline is the piece around the gray disk that is transporting the little balls. It is called a flex spline because the wave generator forces it to flex into an ellipse. Industrial strain wave gears are of course made of metal, and the flex spline does not get quite as deformed by the wave generator as this one. The 1/8 reduction ratio also exaggerates the deformation.

We covered one of [Akiyuki]’s larger GBCs a few years ago. While that one is definitely impressive, this strain wave gearing module is quite the engineering marvel.


Filed under: misc hacks, toy hacks

Maybe You Can Print in Metal

15 hours 38 minก่อน

Let’s face it. Printing in plastic is old hat. It is fun. It is useful. But it isn’t really all that exotic anymore. The real dream is to print using metal. There are printers that handle metal in different ways, but they aren’t usually practical for the conventional hacker. Even a “cheap” metal printer costs over $100,000. But there are ways you can almost get there with a pretty garden-variety printer.

There’s no shortage of people mixing things into PLA filament. If you have a metal hot end and don’t mind wearing out nozzles, you can get PLA filament with various percentages of metal powder in it. You can get filament that is 50% to 85% metal and produce things that almost seem like they are made from metals.

[Beau Jackson] recently had a chance to experiment with a metal-bearing filament that has a unique twist. Virtual Foundry’s Filamet has about 10% PLA. The remaining material is copper. Not only do you have to print the material hot, but you have to print it slow (it is much denser than standard PLA). If it were just nearly 90% metal, that would be impressive, but nothing too exciting.  The real interesting part is what you can do after the print is complete. (If you don’t want to read, you can always skip to the videos, below.)

If you do nothing, you still wind up with a metal-like print. If you have access to a kiln, though, you can put  your part in at nearly 1000 degrees C along with the company’s proprietary “magic black powder.” This removes nearly all the PLA and leaves a completely (99.9%) metal object.

If you prefer, you can also sand and polish the material to bring out the metal appearance, which might be easier than slaving over a hot kiln. Either way, the results do look (and sound) like metal.

The company claims other metals are in development. This isn’t quite as awesome as having a printer that really spews molten metal, but it is a lot more affordable. Not that it is very cheap, mind you. A 750 g spool of material is $85. Sure beats electroplating, though.

 


Filed under: 3d Printer hacks

This DIY Wearable Assist Goes Beyond Traditional Therapy

17 hours 7 minก่อน

Bodo Hoenen and his family had an incredible scare. His daughter, Lorelei, suddenly became ill and quickly went from a happy and healthy girl to one fighting just to breathe and unable to move her own body. The culprit was elevated brain and spinal pressure due to a condition called AFM. This is a rare polio-like condition which is very serious, often fatal. Fortunately, Lorelei is doing much better. But this health crisis resulted in nearly complete paralysis of her left upper arm.

Taking an active role in the health of your child is instinctual with parents. Bodo’s family worked with health professionals to develop therapies to help rehabilitate Lorelei’s arm. But researching the problem showed that success in this area is very rare. So like any good hacker he set out to see if they could go beyond the traditional to build something to increase Lorelei’s odds.

What resulted is a wearable prosthesis which assists elbow movement by detecting the weak signals from her bicep and tricep to control an actuator which moves her arm. Help came in from all over the world during the prototyping process and the project, which was the topic of Bodo Hoenen’s talk at the Hackaday SuperConference, is still ongoing. Check that out below and the join us after the break for more details.

The core concept is to provide assistive feedback which will help Loreli’s body get better at relearning how to command her affected bicep and tricep.

Challenges

There’s a hard limit on weight for this project. That’s because too much weigh on the shoulder and it can be pulled out of the socket due to the current weakness. Hopefully this will also improve with time, but for now the assistive device needs to weigh less than 150 grams.

The actuator must be able to move the mass of her forearm (about 400 g). Input should come from the bicep and tricep using electromyography. They also want a relatively long battery life of at least five hours, and for the final product to look nice, lest she not want to wear it.

No Prior Experience

How do you build something with no prior experience? For regular Hackaday readers that’s not a real question… we do it all the time. Bodo didn’t have experience with most of what went into this project, but cites his entrepreneurial experiences in tackling hard problems. The trick is to learn what it is you don’t know and then ask for help in those areas when needed.

What we really like is that he didn’t just build this for her but built it along with her. The two of them started researching what kind of things other people had built: how people were taking muscle signals and using them to move things. They came up with some ideas, when hitting road blocks they asked for help and the world responded.

They received help in learning how to 3D scan Lorelei’s arm for the best fit. A company in Canada sent them some actuators that met their weight, size, and power constraints. When they tested out the EMG sensors they discovered the signals on her damaged arm were almost completely lost in the noise. Again, help came in from a company working on a very similar problem. A new seventeen-sensor method was adopted that uses machine learning to find those signals. Most recently they have turned this into a video game — Lorelei is retraining her body by moving an arm onscreen. Gamification of physical rehab? Yes please!

The physical prototype is moving right along. It was first assembled with Fischer Technik. With that proof in hand they 3D printed a lattice out of PLA. This was designed from the 3D scan of her arm, printed flat, then submerged in boiling water to soften it before being molded to a full-sized cast of her arm. The result is visually pleasing, light weight, sturdy, and well-fit to her arm.

It is very rare that children who have loss of muscle control from this condition are able to gain it back. But some progress has already been made. We think it’s amazing to see an outpouring of goodwill to help Bodo and his daughter in this endeavor and it has far-reaching benefits. She is learning a lot about engineering and what is possible in life. And they have built an example for others to follow when they are met with obstacles they need to overcome.


Filed under: cons, Hackaday Columns, Medical hacks

Creating A PCB In Everything: KiCad, Part 2

18 hours 36 minก่อน

This is the continuation of a series where I create a PCB in every software suite imaginable. Last week, I took a look at KiCad, made the schematic representation for a component, and made a schematic for the standard reference PCB I’ve been using for these tutorials. Now it’s time to take that schematic, assign footprints to parts, and design a circuit board.

The completed schematic for our board

All PCB design tools have different methods of associating the schematic view of a component with how it will be represented on the finished board. Eagle uses libraries that contain both a schematic view and PCB view of a component. In the prehistory of PCB design software, Autotrax simply ignored the schematic view.

Click this button to run PCBnew

KiCad has a clear separation between a symbol (the schematic view) and a footprint (the PCB view). If we were to take our schematic and create a new PCB by running PCBnew, nothing would happen – our symbols aren’t associated with any footprints.

Click this button to run CvPCB

To associate symbols with footprints, we need to run CvPCB. This sub-program tucked inside KiCad gives us the ability to associate footprints with our schematic symbols.

CvPCB, with another window open allowing you to view the footprints It’s like the cloud, only not completely worthless

CvPCB is a new feature for KiCad 4.0. Instead of every other PCB design tool we’ve taken a look at so far, KiCad effectively stores all of the footprints in Github. In the Github repo for KiCad, you’ll find a bunch of files with a .pretty file name. These are the footprints for nearly every component you can imagine. If you’re running a fresh install of KiCad, everything shows up in CvPCB automagically – there’s nothing you need to worry about, and footprints just happen.

There’s a subtle brilliance about this implementation. It’s like the cloud, only it’s completely verifiable, and if a part doesn’t work, you can fix it and submit a pull request. Already, this is phenomenally better than the Eagle paradigm, where millions of footprints are available in thousands of different libraries scattered around the Internet. If you’re reading through this series in order, take note: this ‘Github as the cloud’ will be a major point of comparison when we get to other cloud-based PCB design tools.

With that said, we need to associate footprints with the symbols on our schematic. To do that, go down the list in the center of the CvPCB window that contains a list of all the components in our schematic and associate a footprint with each part. Footprints are on the right, libraries (or categories) are on the left. To view the selected footprint in a new window, click the ‘view selected footprint’ button.

Selecting a footprint for the USB port Getting Libraries In Order

This project is using (mostly) all through-hole parts, and as such, I could easily select a DIP8 footprint for the ATtiny85 and be done with the whole thing. This is a tutorial, though, and I need to demonstrate how to make a part – schematic and PCB view – from scratch.

To make a footprint, KiCad offers a Footprint Editor. This can be accessed from either PCBnew or the launcher. Click on that, select File -> New Footprint, enter a name for this footprint (‘ATtiny85’ will do), the name of the footprint and a reference designator is placed onto the footprint editing window.

Libraries are important, and since KiCad is now running on ‘not-worthless cloud technology’, we have to create a library for this project that won’t be saved along with our copies of the standard Github libraries. Select File -> Save Footprint In New Library, save this library wherever the rest of the files are for this project, and give the library a name.

We have just created a new library, but that doesn’t mean KiCad knows what library we’re working with. In the Footprint Editor, select Preferences -> Footprint Libraries Manager, and click on the ‘Project Specific Libraries’ tab. Hit the ‘Append Library’ button, and drop the path to the library we just created in the ‘Library Path’ field. That’s more KiCad weirdness, but once we’re done we can finally create a footprint.

Making The Footprint

Now that we have the Footprint Editor open, a part name and a reference for the footprint, and the library all set up, it’s time to actually put some pads down. There are a few relevant buttons on the screen:

The most important, obviously, is the ‘Add a pad’ button. Click that and drop some pads down where they should be. This is a standard DIP8, or two rows of four pins 0.3″ apart. The default grid, as you may have noticed, is 50mils.

After placing the pads, use the hotkey ‘E’ to edit the properties of each pad. Here, you can change a through-hole part to an SMD, change the dimensions of the pad, hole, and shape of everything. Importantly, the Pad Properties window allows you to change the number of the pad. The number of the pad is how KiCad connects the schematic representation of a part with the footprint. Get this right, or else nothing will work.

Add a few lines to the footprint, save your work in the project library, and go back to the schematic. You’re done. That’s how you make a footprint.

From Schematic To Board

Now that the schematic has footprints associated to everything, it’s time to open up PCBnew, move parts around, and put some traces between parts. Do that. Oh, nothing shows up. Why is that? You need to generate a netlist in the schematic view, and import it in PCBnew. There’s a button with ‘NET’ written on it in both programs. Click those. Now, what do we get when the netlist is successfully imported into PCBnew? The worst mess you’ve ever seen in any sort of design program:

I desperately want to see someone import a netlist for a large project in KiCad.

We end up with a gigantic mess on our hands. No worries, ‘M’ is the hotkey to move the parts around. You can also use the ‘Move Footprint’ mode to automagically place these parts. Reference the PCB we designed for the introduction to this series and move some parts around until we get something resembling the board below. The relevant hokeys are ‘M’ for move and ‘R’ for rotate. As always, there’s the ‘?’ hotkey that tells you everything you need to know.

That’s close, but it looks horrible. Deselect Footprint mode, use your cursor, and move all those labels and references around. We don’t need “CONN-01×04” on the board, and it’s really helpful to have the values of resistors inside their own footprint. With a little bit of work and deleting those labels, you’ll have something that looks like this:

Holy crap, that actually looks like something. All the resistors and diodes are labeled with their value, all the superfluous references are gone, and this actually looks good. You can’t do this in Eagle easily.

With the layout pretty much figured out, it’s time to finally draw some traces. This requires a description of the layers.

  • F.Cu and B.Cu are the top and bottom copper layers. The hotkeys for these layers are PgUp and PgDn
  • Edge.Cuts is the equivalent of the ‘Milling’ layer in Eagle. This is the outline of your board.
  • F.SilkS and B.SilkS is the silkscreen – the text and outlines of your components.
  • F.Mask and B.Mask is the soldermask. It’s usually green, or purple from OSHPark.
  • F.Adhes and B.Adhes is glue applied to SMD components.
  • F.Paste and B.Paste is where solder paste will be applied.

For a simple board that won’t be sent off to an assembly house, the only layers you need to worry about are the copper layers, the Edge.Cuts, and the silkscreen.

The first thing to do to complete the board is to draw the ‘edge’ or milling layer. Select the ‘Add a graphic line’ button on the right hand toolbar, and draw a rectangle around all our parts. That’s simple enough.

Now it’s time to actually put some traces down. You can select which copper layer to use in the top toolbar, and the relevant hotkey is ‘X’. Hit ‘X’, click on a few airwires, and route them just like the reference PCB. Don’t worry about power or ground traces – we’re going to do those with copper fills. When you’re done, you should have something like this:

That’s pretty much all there is to it, save for the copper fills. To do that, we need to add a ‘filled zone’ or ‘copper pour’ or a ‘polygon’. By any other name, it’s just a big area of copper that is connected to a single net in the schematic.

Click on the ‘Add filled zones’ button, and a ‘Copper Zone Properties’ window will show up. Here, you can assign a layer of copper to a specific signal. Our board puts +5V on the back copper, and GND on the front copper. In the Copper Zone Properties, select the B.Cu layer, the +5V net, hit Ok, and trace around the edge of the board. Do the same with the F.Cu layer and the GND net. When those fills become hatches around the edges of the board, hit the ‘B’ hotkey to render the copper fills.

That’s it. We are technically done. If you save and drag the .kicad_pcb file onto the OSHPark web page you’ll get a pretty purple PCB in a week or two. That’s not to say this PCB actually works – I screwed up the USB signals in the schematic, and that propagated over to the PCB. No matter, because no one is actually going to build one of these boards.

This just about concludes the ‘Creating A PCB in Everything’ tutorial for KiCad. If you’ve been reading along for the last five thousand words, you have an excellent introduction to KiCad, and should at least be able to build a breakout board. This doesn’t mean I’m done with KiCad quite yet – there are a few more tricks to go over including DRC and ERC, a demo of how freakin’ awesome the routing in KiCad is, and I need to put a keepout on the decoupling cap in on the board, anyway. Creating a PCB in Everything: KiCad Part 3 (the optional part) will be out sometime next week.

Thoughts on KiCad

This series of posts serves two purposes. First, it is a quick tutorial for various PCB design tools. After reading these posts, you should be able to guess your way through a PCB design tool and build a simple PCB. Second, each of these tutorials serves as a pseudo-review of each PCB design tool. Each of these posts serves to illuminate the quirks of a PCB design tool, and serves as a notice that I still have an unclaimed bounty for the first person to create a part for an ATtiny85 from scratch in Fritzing. Don’t use Fritzing, it sucks.

Coming from Eagle, KiCad is downright weird. That’s not to say it’s difficult, though – it’s generally the same as any other PCB design tool. The interface, like nearly every Open Source project, is obtuse, and there are five non-obvious ways to complete any task. There is zero reason why parts imported from a netlist into a board are squished together. Custom libraries can and should be automatically imported. The KiCad community especially rancorous. The UI suffers from an intangible wrongness about it, although that seems to lessen after working with it for a few hours. In a sense, KiCad is exactly what you would expect from an Open Source project that is decades old, very mature, and has features packed to the gills: it’s very powerful, but not friendly to the beginner.

Although the KiCad beginner will struggle to wrap their heads around the interface, it will be one of the most powerful PCB design tools I’ll use in this series of posts. No other free (beer) program will give you 32 copper layers and unlimited routing space. Nothing else uses the cloud/GitHub like KiCad. It’s brilliant.

A few months ago, if someone asked me to suggest a PCB design tool, I’d give Eagle or KiCad as suggestions. Eagle is easy enough to learn, and will be getting better since the Autodesk acquisition. KiCad is robust, and even in the best case of Eagle development, Autodesk may only ever reach parity with what KiCad can do.

Now, KiCad is growing on me. I have a secret project where I need to build and manufacture a thousand relatively complex boards. My previous go-to was Eagle, but I think I’m going to do this board in KiCad.


Filed under: Hackaday Columns, how-to, Skills

RainCube Spreads Its Umbrella

ศุกร์, 12/09/2016 - 23:30

There are times when a mechanism comes to your attention that you have to watch time and time again, to study its intricacies and marvel at the skill of its designer. Sometimes it can be a complex mechanism such as a musical automaton or a mechanical loom, but other times it can be a device whose apparent simplicity hides its underlying cleverness. Such a moment came for us today, and it’s one we have to share with you.

RainCube is a satellite, as its name suggests in the CubeSat form factor and carrying radar instruments to study Earthly precipitation. One of the demands of its radar system is a parabolic dish antenna, and even at its 37.5 GHz  that antenna needs to be significantly larger than its 6U CubeSat chassis.

The unfolding parabola in action.

It is the JPL engineers’ solution to this problem that is the beautiful mechanism we want to show you. The parabola is folded within itself and tightly furled round the feedhorn within the body of the satellite. As the feedhorn emerges, first the inner sections unfurl and then the outer edge of the parabola springs out to form the dish antenna shape. Simultaneously a mechanism of simplicity, cleverness, and beauty, one we’d be very proud of if it were our creation.

There is nothing new in collapsible parabolas used in spacecraft antennas, petal and umbrella-like designs have been a feature of some of the most famous craft. But the way that this one has been fitted into such a small space (and so elegantly) makes it special, we hope you’ll agree.

[via space.com]


Filed under: radio hacks

Diodes: The Switch You Never Knew You Had

ศุกร์, 12/09/2016 - 22:01
Vishay’s take on the 1N4148 data sheet (PDF), describing it as a switching diode.

When looking across the discrete components in your electronic armory, it is easy to overlook the humble diode. After all, one can be forgiven for the conclusion that the everyday version of this component doesn’t do much. They have none of the special skills you’d find in tunnel, Gunn, varicap, Zener, and avalanche diodes, or even LEDs, instead they are simply a one-way valve for electrical current. Connect them one way round and current flows, the other and it doesn’t. They rectify AC to DC, power supplies are full of them. Perhaps you’ve also used them to generate a stable voltage drop because they have a pretty constant voltage across them when current is flowing, but that’s it. Diodes: the shortest Hackaday article ever.

Not so fast with dismissing the diode though. There is another trick they have hiding up their sleeves, they can also act as a switch. It shouldn’t come as too much of a shock, after all a quick look at many datasheets for general purpose diodes should reveal their description as switching diodes.

So how does a diode switch work? The key lies in that one-way valve we mentioned earlier. When the diode is forward biased and conducting electricity it will pass through any variations in the voltage being put into them, but when it is reverse biased and not conducting any electricity it will not. Thus a signal can be switched on by passing it through a diode in forward bias, and then turned off by putting the diode into reverse bias.

Diode Switch Basics A simplified diode switch in the reverse biased Off position.

To illustrate a basic diode switch, we’ve prepared a couple of simplified circuit diagrams. The first shows the anode tied to ground through R1 and the cathode tied to the Vcc power rail. The diode is in reverse bias, and no current is flowing through it. An AC voltage applied to C1 will appear at the anode, but will not appear at the cathode and the output via C2. The switch, in this case, is off.

The second diagram shows a very similar circuit but with the resistors connected to the opposite supply lines. The anode is now tied to the Vcc rail and the cathode to ground. A current is flowing through the diode, and it is forward-biased. Thus an AC voltage applied to C1 will appear at both the anode and cathode of the diode, and will make it through C2 to the output. The switch has been turned ON.

A simplified diode switch in the forward biased On position.

This is a simplified circuit, but not by much. A practical diode switch usually works by maintain one side of the diode at a bias point so that when a logic level is applied to the other point it will switch the diode from forward to reverse bias to allow the switch to be electronically controlled. In other words, hold one end of the diode in the middle, waggle the other end high or low.

Particularly for RF circuits you will also find RF chokes in the bias lines to stop RF finding its way into the power and logic circuits. But the essence is there in the diagrams, diode switches really are that simple.

So now you know how diodes can be used as simple on-off switches. You can even make multi-way  switches by connecting single diode switches in parallel to a single bias point. But that’s not the limit of the capabilities of the humble diode when it comes to switching, so we’ll now consider a couple more applications.

Diodes: They’re Only Logical

The first electronic digital computers such as those you would have found in military installations or universities in the 1940s used vacuum tubes, sometimes in conjunction with relays or other electromechanical components. As computers evolved through the early 1950s and found their way into civilian applications they started to be produced using the much smaller and less power-hungry semiconductors which were then the new kid on the block. The trouble with transistors of the 1950s though was that they were both expensive and unreliable, instead of the super-reliable planar silicon transistors we are used to today. The early 1950s designer had to work with germanium point-contact transistors. These devices, aside from their fragility, had the unfortunate characteristic of latching in the logic high state and requiring a power supply refresh after a state change. Clearly any circuitry that could reduce reliance on them was of great interest.

The diode OR gate. Thingmaker [CC BY-SA 4.0], via Wikimedia Commons.To the rescue of those 1950s designers came the humble diode. They were cheaper and far more reliable than a point-contact transistor, and capable of forming AND and OR gates with only resistors for company. This so-called diode-resistor logic, or DRL, was used in solid-state computers everywhere possible during this period, with transistors used only where an inverter was required.

Both diode gates use the diodes on their input lines, bringing the other ends of the diodes together at an output point with a pull-up or pull-down resistor.

The diode OR gate has the anodes facing the inputs and a pull-down resistor on the output, while the AND gate has the cathodes facing the inputs and a pull-up resistor on the output.

The diode AND gate. Thingmaker [CC BY-SA 4.0], via Wikimedia Commons.Aside from requiring a transistor whenever a logic inversion is required, these gates suffer the problem that there is a voltage drop across each gate. Thus if you daisy-chain a series of diode gates you will find that with each layer the logic levels drop, eventually to a point at which their transition is not sufficient to operate successive gates.

It is however still worth having diode logic in your stock of available circuits, for sometimes you may have a requirement for a single AND or OR in a project and it may make sense to quickly put one together using a few diodes rather than another 74 series chip.

Mixing it up with diodes A diode mixer or ring modulator.

There is a further place that you will encounter a diode switch, especially if you are interested in radio or electronic music. The diode bridge mixer or ring modulator is a circuit using four diodes in a similar configuration to that you’d find in a bridge rectifier, and it functions as a frequency mixer in which an AC signal and the output of an oscillator are mixed to create their sum and their difference. The four diodes act as switches between the balanced signal input and the output, and have the effect of reversing the polarity of the path between them on each cycle of the local oscillator. It is used in synthesisers and guitar pedals, and in radio circuits wherever a transition between frequencies is required.

We hope you’ll now look at those diodes in your junk box with new respect now you know they can also do a good job of switching. You may never use a diode as a switch in practice, but it’s good to be familiar with the concept. And if diodes have caught your interest, why not continue with a look at our recently-published history of the diode?


Filed under: Engineering, Featured, parts

Laser Cutting a Wooden Dymaxion Globe

ศุกร์, 12/09/2016 - 19:00

Everyone knows that globes are cool — what else would you use as the centerpiece of your library/study? But, sadly, making your own isn’t a simple process. Even if you had a large (preferably hollow) sphere to work with, you’d still have to devise a clever way of printing the map in sections that can be glued to the curved surface. Wouldn’t it be easier if you could just laser cut flat sections, and assemble them to form a faceted “globe?”

Well, it is, and you can! Because, [Gavin] over at tinkerings.org (a Hackaday favorite) has created the files to do just that! This map projection, originally designed by the very interesting Buckminster Fuller, is designed to be either laid flat or three-dimensionally on an icosahedron (a 20-sided polyhedron). That makes it perfect for laser cutting, as each of the 20 faces can be cut from flat stock.

After the faces are cut (and marked with the laser cutter), they can be assembled with 3D-printed vertices and simple machine screws. The final product is an accurate three-dimensional map that looks cool and is chock-full of interesting history and cartographic principles. Of course, if you want to up the technological ante, you could always build an interactive globe!


Filed under: laser hacks

Christmas Lights Done the Hard Way

ศุกร์, 12/09/2016 - 16:01

It’s that time of the year again when you gotta start worrying if you’ve been naughty enough to not receive any gifts. Hopefully, Blinky Lights will appease St. Nick. Grab a strip of RGB LEDs, hook them up to an Arduino and a Power supply, slap on some code, and Bob’s your Uncle. But if you want to retain your hacker cred, you best do it the hard way. Which is what [roddersblog] did while building his Christmas Starburst LED Stars this year — and bonus points for being early to the party.

For starters, he got panels (as in PCB panels) of WS2812 boards from eBay. The advantage is it lets you choose your own pitch and strand length. The flip side is, you need to de-panel each board, mount it in a jig, and then solder three lengths of hook up wire to each LED. He planned for an eight sided star with ten LED’s each. And he built three of them. So the wiring was, substantial, to say the least. And he had to deal with silicone sealant that refused to cure and harden. But nothing that some grit and determination couldn’t fix.

For control, he choose the PIC16F1509 microcontroller. This family has a feature that PIC calls the “Configurable Logic Cell” and this Application Note describes how to use CLC to interface the PIC to a WS2811. He noticed processing delays due to C code overheads that caused him some grief. After some experimentation, he re-wrote the entire program in assembly which produced satisfactory results. You can check out his code on the GitHub repository.

Also well worth a look, he’s got a few tricks up his sleeve to improve the quality of his home-brew PCB’s. He’s built his own UV exposure unit with timer, which is an interesting project in itself. The layout is designed in Eagle, with a flood fill to minimize the amount of copper required to be etched away. He takes a laser print of the layout, applies vegetable oil to the paper to make it more translucent to UV, and doubles up the prints to get a nice contrast.

Once the sensitized board has been exposed in the UV unit, he uses a weak but fresh and warm solution of Sodium Hydroxide as a developer to remove the unexposed UV photo-resist. To etch the board, he uses standard Feric Chloride solution, which is kept warm using an aquarium heater, while an aquarium air-pump is used to agitate the solution. He also describes how he fabricates double sided boards using the same technique. The end result is quite satisfying – check out the video after the break.


Filed under: led hacks, Microcontrollers

No-Etch Circuit Board Printing

ศุกร์, 12/09/2016 - 13:00

If you’ve ever tried to build a printed circuit board from home, you know how much of a pain it can be. There are buckets of acid to lug around, lots of waiting and frustration, and often times the quality of the circuits that can be made traditionally with a home setup isn’t that great in the end. Luckily, [Rich] has come up with a way that eliminates multiple prints and the acid needed for etching.

His process involves using a laser printer (as opposed to an inkjet printer, as is tradition) to get a layer of silver adhesive to stick to a piece of paper. The silver adheres to the toner like glitter sticks to Elmer’s glue, and allows a single pass of a laser printer to make a reliable circuit. From there, the paper can be fastened to something more solid, and components can be reflow soldered to it.

[Rich] does post several warnings about this method though. The silver is likely not healthy, so avoid contact with it, and when it’s applied to the toner an indeterminate brown smoke is released, which is also likely not healthy. Warnings aside, though, this is a great method for making home-made PCBs, especially if you don’t want tubs of acid lying around the house, however useful.

Thanks to [Chris] for the tip!

 


Filed under: chemistry hacks

Nylon Fibre Artificial Muscles — Powered by Lasers!

ศุกร์, 12/09/2016 - 10:00

If only we had affordable artificial muscles, we might see rapid advances in prosthetic limbs, robots, exo-skeletons, implants, and more. With cost being one of the major barriers — in addition to replicating the marvel of our musculature that many of us take for granted — a workable solution seems a way off. A team of researchers at MIT present a potential answer to these problems by showing nylon fibres can be used as synthetic muscles.

Some polymer fibre materials have the curious property of increasing in  diameter while decreasing in length when heated. Taking advantage of this, the team at MIT were able to sculpt nylon fibre and — using a number of heat sources, namely lasers — could direct it to bend in a specific direction. More complex movement requires an array of heat sources which isn’t practical — yet — but seeing a nylon fibre dance tickles the imagination.

There are numerous other challenges to tackle — namely wear — on the path to creating artificial muscles, so each research vector is worthy of due consideration. For further reading, our own Moritz Walter recently outlined a number of different options for artificial muscles.

[via Gizmodo]


Filed under: Uncategorized

VGA Monitor Becomes Drawing Toy

ศุกร์, 12/09/2016 - 07:00

We hate to break it to [Rob Cai], but he’s built a VGA drawing toy, not an Etch-a-Sketch. How do we know? Simple, Etch-a-Sketch is a registered trademark. Regardless, his project shows how an Arduino can drive a VGA monitor using the VGAx library. Sure, you can only do four colors with a 120×60 resolution, but on the other hand, it requires almost no hardware other than the Arduino (you do need four resistors).

The hardware includes two pots and with the right firmware, it can also play pong, if you don’t want to give bent your artistic side. You can see videos of both the art toy and the pong game, below.

Because the device started as a pong game, [Rob’s] version has two boxes, each with a pot and a button. Of course, if you were really building it just for the drawing toy, you’d probably put it all in a box. Maybe even a red box. If we were building it, we’d be tempted to put a tilt sensor or an accelerometer in the box so you could shake it to erase the picture. Just saying.

If you want 640×480 resolution from an Arduino, it can be done, but it takes more hardware. If you were trying to get a kid interested in Arduino, you could do worse than start with two projects with video that are fun, use a handful of easy-to-source parts, and shares hardware. Then again, if you are in the “go big or go home” camp, we’d redirect to this pong game, instead.


Filed under: Arduino Hacks

That NASA EM Drive Paper: An Expert Opinion

ศุกร์, 12/09/2016 - 04:00

A week or two ago we featured a research paper from NASA scientists that reported a tiny but measurable thrust from an electromagnetic drive mounted on a torsion balance in a vacuum chamber. This was interesting news because electromagnetic drives do not eject mass in the way that a traditional rocket engine does, so any thrust they may produce would violate Newton’s Third Law. Either the Laws Of Physics are not as inviolate as we have been led to believe, or some other factor has evaded the attempts of the team to exclude or explain everything that might otherwise produce a force.

As you might imagine, opinion has entrenched itself on both sides of this issue. Those who believe that EM drives have allowed us to stumble upon some hitherto undiscovered branch of physics seized upon the fact that the NASA paper was peer-reviewed to support their case, while those who believe the mechanism through which the force is generated will eventually be explained by conventional means stuck to their guns. The rest of us who sit on the fence await further developments from either side with interest.

Over at Phys.org they have an interview from the University of Connecticut with [Brice Cassenti], a propulsion expert, which brings his specialist knowledge to the issue. He believes that eventually the results will be explained by conventional means, but explains why the paper made it through peer review and addresses some of the speculation about the device being tested in space. If you are firmly in one of the opposing camps the interview may not persuade you to change your mind, but it nevertheless makes for an interesting read.

If EM drives are of interest, you might find our overview from last year to be an illuminating read. Meanwhile our coverage of the NASA paper should give you some background to this story, and we’ve even had one entered in the Hackaday Prize.


Filed under: news, transportation hacks

Bitbanging VGA Fits In under 1 kB

ศุกร์, 12/09/2016 - 03:15

Don’t throw those old VGA monitors away, turn them into works of art with [danjovic] and VGA Blinking Lights. This circuit uses a PIC16F688 to generate VGA video. Not just a random spray of monochrome dots either. VGA Blinking Lights puts up an ever-changing display of 48 colored squares.

Originally created for the square inch contest, VGA Blinking Lights could hide behind a quarter. [Danjovic] dusted his project off and entered it in The 1 kB Challenge. The code is written in PIC assembly. The final hex used to generate the squares clocks in at 471 words. Since the PIC uses a 14 bit word, that’s just over 824 bytes. Plenty of space for feature creep!

Video is generated with a twist on the R2R DAC. [Danjovic] tweaked the resistor values a bit to obtain the correct voltage levels for the VGA standard. The color of the squares themselves are random, generated using a Galois Linear Feedback Shift Register (LFSR).

With only a handful of components, and a BOM cost under $5, this would be a fun evening project for any hardware hacker.

If you have a cool project in mind, there is still plenty of time to enter the 1 kB Challenge! Deadline is January 5, so check it out and fire up your assemblers!


Filed under: video hacks

Hacking Your Way Through NASA

ศุกร์, 12/09/2016 - 02:31

The 2016 Hackaday SuperConference took place last month in sunny Pasadena, California. Also calling Pasadena home is the Jet Propulsion Laboratory, the place where Mars rovers are built, where probes are guided around the solar system, and where awesome space stuff happens.

JPL had a large contingent at the SuperCon and two of them teamed up to present their talk: Charles Dandino and Lucy Du. Lucy is a mechatronics engineer at JPL and already has a little bit of fame from fielding a Battlebot in the last two seasons of ABC’s series. Charles is also in mechatronics, with experience with Curiosity, the Mars 2020 rover, and the (hopefully) upcoming asteroid redirect mission.

In their talk, Charles and Lucy uncovered some of the hacks happening in the background at JPL. There’s a lot of them, and their impact goes much further than you would expect. Everything from remote control cars to keeping spacecraft alive on the other side of the solar system.

As far as recent NASA hacks go, an interesting problem cropped up during the development of the Ares I rocket, the ‘small’ crew launch vehicle of the canceled Constellation program. During the development of the rocket, engineers noticed the gigantic solid rocket booster powering the first stage caused massive oscillations in the crew capsule. Structurally, everything was fine, but humans are weak bags of mostly water, and astronauts couldn’t read the digital displays when subjected to these vibrations.

The most obvious solution to this problem would be to fix the oscillations in the rocket. This, however, would require an enormous amount of effort, for something as simple as fixing the pilot’s blurry vision. A much better solution was found, using cheap, off-the-shelf parts and a bit of code. By strapping accelerometers onto the seats in the crew capsule, the frequency of the rocket’s oscillations was measured and the digital displays were strobed at the same frequency. That was enough to fix the problem, and it did so using only a very few very inexpensive parts.

What’s the coolest improvised engineering coming out of JPL today? Charles is working on the asteroid redirect mission, and that means figuring out a way to grab an asteroid and tow it back to somewhere around Earth. To do that, the team needs to test their equipment and that means making their own batch of asteroids.

We don’t really have a lot of data on the surface composition of asteroids. Sure, NASA has landed crashed into asteroids very, very slowly, and the ESA recently tried to land the Philae lander on a comet without much success. Generally, we have an idea of what the surface of an asteroid should feel like, and to test the grippers for the asteroid redirect mission, JPL is developing their own mix of foamed concrete. It’s soft, flaky, and completely unlike anything on Earth that has been subjected to four Billion years of geology.

Elsewhere around JPL, engineers are building models for equipment they hope will be part of a mission in the future. These models range from cheap remote control cars laden with very expensive sensor packages to Hot Wheels cars retrofitted with 3D printed parts and gears.

There’s a long tradition of experimentation at JPL. The first Mars rover — Sojourner, the tiny shoebox-sized robot carried along the Mars Pathfinder mission — had a new, innovative rocker-bogie suspension system. When the mission was in the planning stages, there were a few questions if this suspension system would work. Those fears were allayed once an engineer brought in a working model of this new kind of rover.

All in all, Charles and Lucy presented a great talk on what makes space stuff work. If you’re looking for the weirdest, most creative applications of non-standard engineering, you don’t need to look any further than NASA and JPL.


Filed under: cons, Featured

Sensing a Magnet with Local Sourcing

ศุกร์, 12/09/2016 - 01:01

I had a small project going on–never mind exactly what–and I needed to detect a magnet. Normally, that wouldn’t be a big problem. I have a huge hoard of components and gear to the point that it is a running joke among my friends that we can be talking about building something and I will have all the parts we need. However, lately a lot of my stuff is in… let’s say storage (again, never mind exactly why) and I didn’t have anything handy that would do the job.

Options

If I had time, there are plenty of options for detecting a magnet. Even if you ignore exotic things like SQUID (superconducting quantum interference device) there’s plenty of ways to detect a magnet. One of the oldest and the simplest is to use a reed switch. This is just a switch made with a thin piece of ferrous material. When a magnet is nearby, the thin piece of metal moves and makes or breaks the contact.

These used to be common in alarm systems to detect an open or closed door. However, a trip to Radio Shack revealed that they no longer carry things like that as–apparently–it cuts into floorspace for the cell phones.

I started to think about robbing a sensor from an old computer fan or some other consumer item with a magnetic sensor onboard. I also thought about making some graphene and rolling my own Hall effect sensor, but decided that was too much work.

Browsing

I was about to give up on Radio Shack, but decided to skim through the two cabinets of parts they still carry just to get an idea of what I could and could not expect to find in the future. Then something caught my eye. They still carry a wide selection of relays. (Well, perhaps wide is too kind of a word, but they had a fair number.) It hit me that a relay is a magnetic device, it just generates its own electromagnetic field to open and close the contacts.

I picked up a small 5 V reed relay. They don’t show it online, but they do have several similar ones, so you can probably pick up something comparable at your local location. I didn’t want to get a very large relay because I figured it would take more external magnetic field to operate the contacts. You have to wonder why they have so many relays, unless they just bought a lot and are still selling out of some warehouse. Not that relays don’t have their use, but there’s plenty of better alternatives for almost any application you can think of.

The Fridge Test

I got home and pulled a rare earth magnet off the refrigerator and grabbed an ohm meter. Sure enough, I could reliably operate the relay contacts with the strong magnet. My project was in business!

Of course, your mileage may vary. The construction of any particular relay may or may not be conducive to external activation. You may have to experiment with the exact magnet, but those are easy to find in lots of local outlets, including home improvement and hobby stores.

The Mother of Invention

When you are cooking, sometimes it helps to know that you can substitute one thing for another. The same is true of electronic components. Need a bridge rectifier? Make one out of diodes. You can probably substitute an op amp for most comparator applications. LEDs can detect light and speakers can act as microphones although in both cases the results are not as good as  parts that are supposed to do those functions.

I do think it is interesting, though, that Radio Shack has such a blend of odd things. You can get a lot of Arduino shields, for example. You can also get a lot of relays. However, I noticed there was only one MOSFET in the cabinet and it wasn’t a “logic level” FET. Seems like it would be like going into an office supply store and finding PCs and carbon paper, but no LCD screen wipes.

Regardless of Radio Shack’s ability to keep up with the times or not, I was glad they had relays. When you are looking to scrounge something in a hurry, don’t forget to think about auto supply places, home improvement stores, craft stores, and even dollar stores — I’ve seen a one-dollar, open-door detector before, but I knew from a previous attempt they have the sensor integrated with the electronics and are hard to scrounge.

Postscript: After I completed my little project, while looking for something totally unrelated, I ran across this homebrew reed switch. Certainly another option.

 

 


Filed under: rants

Absolute Power

พฤ, 12/08/2016 - 23:31

We recently noticed a very cool-looking series of power supply modules on a few of the Chinese deal web sites. Depending on the model, they provide a digitally-controlled voltage with metering. You need to provide at least a volt or so over the maximum desired output voltage. You can see a video from [iforce2d] below. The module in the video is rated for 5A at 50V maximum, but there are other sizes available. For those interested in graphs and numbers [lgyte] did a lot of characterization of these modules.

There was a time when importing goods from far away places was somewhat of an art. Finding suppliers, working out payment, shipping, and customs meant you had to know what you were doing. Today, you just surf the web, find what you want, pay with PayPal, and stuff shows up on your doorstep from all four corners of the globe.

There is one problem, though. We see a lot of cool stuff from China and some of it is excellent, especially for the price. Frankly, though, some of it is junk. It is hard to tell which is which. What’s more is even though in theory you might be able to return something, usually the freight charges make that impractical. So when you get a dud, you are likely to just eat it and chalk it up to experience. So the question is: how good (or bad) or these power supply modules?

The video is a good way to see what you are getting. Certainly, you get a better idea of the size of the module. However, what’s it look like electrically? The testing from [lgyte] is very comprehensive and not only includes graphs of key parameters but also IR photos of the circuit board to identify hot spots. There’s also a longer video about a similar module from [neutronstorm], below.

For the low price, the features of these supplies look good. You can set the supply to shut down when you exceed a voltage, current, or power limit. The DPS series modules have a slightly improved user interface compared to the DP series.

We’ve seen digital power supplies before (including some nicely packaged ones), of course. However, these are cheap, look good, and would be dead simple to use. A transformer, bridge rectifier, and filter capacitors on the input of one of these and you are set. For many applications, an old 18.5V laptop power brick would be a great way to feed one of these.


Filed under: tool hacks

Measuring High Voltage in Millimeters (and Other HV Probe Tricks)

พฤ, 12/08/2016 - 22:01

I work a lot with high voltages and others frequently replicate my projects, so I often get asked “What voltage is needed?”. That means I need to be able to measure high voltages. Here’s how I do it using a Fluke high voltage probe as well as my own homemade probe. And what if you don’t have a probe? I have a solution for that too.

How Long Is Your Spark?

The simplest way to measure high voltage is by spark length. If your circuit has a spark gap then when a spark occurs, that’s a short-circuit, dumping all your built up charge. When your spark gap is at the maximum distance at which you get a spark then just before the spark happens is when you have your maximum voltage. During the spark the voltage rapidly goes to zero and depending on your circuit it may start building up again. The voltage before the spark occurred is related to the spark length, which is also the spark gap width.

The oscilloscope photo below shows this changing voltage. This method is good for a rough estimate. I’ll talk about doing more precise measurements when I talk about high voltage probes further down.

But it’s not quite so simple. The shape of the electrodes plays a big part, as does the pressure and temperature of whatever is in the gap, usually air. For flat electrodes, or spherical electrodes whose diameter is significantly greater than the gap size, in air at 25C (77F), the following formula can be used:

voltage (kV) = 3 x pressure x spark length + 1.3√spark length

The pressure is in units of atmospheres and the spark length is in millimeters. Most hackers work at atmospheric pressure which is 1 atm, so that can be left out of the formula. Also, for a 10mm spark gap, for example, taking the square root of 10mm and multiplying by 1.3 means you’re adding an insignificant 4.1. And so the formula is usually simplified to just:

voltage (kV) = 3 x spark length (in mm)

or for centimeters:

voltage (kV) = 30 x spark length (in cm)

That’s just another way of saying that there’s 30kV/cm. For inches, the formula is:

voltage (kV) = 76.2 x spark length (in inches) voltage (kV) = 11.8 x spark length (in inches)

In the photos above, the measured voltage is 17kV. The spark gap width (i.e. the spark length) is measured as just under 5mm. If we apply the formula for a 5mm spark gap, we get 3 x 5mm = 15kV. The larger the spheres, the closer the measurement should match the formula, for a certain voltage range, but more on that below.

However, if you use sharper electrodes such as needles or rods, then at sufficient voltages the electric field between the electrodes will be less uniform and in places will be strong enough to ionize some of the air in the gap. That essentially creates a high resistance short-circuit which means your voltage will be lowered. The formula above will no longer apply. In that case you can try looking up your spark length and electrode configuration in a chart.

Spark gap width to voltage chart

The above chart summarizes all of this. The bottom line in dark blue is the line according to the formula (essentially 30kV/cm):

voltage (kV) = 30 x spark length (in cm)

That formula defines a linear relationship between spark length and voltage. It looks like there’s a bend upward at 50kV but that’s because the voltage scale below 50kV increments by 5 and above 50kV it increments by 10. Above that is the real data. As you can see, needle electrodes follow the formula the least. The larger the sphere diameter, the higher the voltage they get to before they no longer closely follow the 30kV/cm line. Most of my work these days is below 30kV, though my electrodes are rarely big spheres, as is the case for most hackers. That is unless you’re working with Van de Graaff generators, but even then usually only the dome is spherical and the other electrode isn’t.

Using A Fluke High Voltage Probe The Fluke 80K-40 HV probe

For more precise measurements I use a Fluke 80K-40 high voltage probe. This one is designed for use from 1kV to 40kV DC, with accuracy varying from 1% to 2% depending on the temperature, and not including the accuracy of the meter. For AC it’s designed for peak AC, 20kV RMS and gives an accuracy at 60Hz of +/-5%. The input resistance is 1000MΩ. It’s for use with a 10MΩ +/-1.0% voltmeter, or oscilloscope as in the photos above. Meters with other impedances can be used with the help of an external shunt or a correction factor, all of which is described in the probe’s documentation.

When making the measurement, take the reading on the meter or oscilloscope and multiply it by 1000. That’s how I went from the 17V shown on the scope to 17kV in the example above.

Here are two more photos of where I’ve used the Fluke probe. One is with a 10MΩ FET analog meter for measuring the voltage across a smoke precipitator. The other is with the analog meter again but I’m holding the probe in my hand. I’m measuring the voltage across a lifter that’s being provided by a PC monitor power supply.

A Homemade High Voltage Probe Using the DIY high voltage probe

The Fluke is good for up to 40kV DC but I’ve had to measure higher and so I made my own probe. The highest I’ve used it for is 75kV DC, though it’s designed for a maximum of 150V at the meter, which equates to an input voltage of 150kV.

High voltage probe design

The above is how it was designed. R1 has a very high resistance compared to the meter’s impedance of 10MΩ (R3) and the resistor that the meter is measuring across, also 10MΩ (R2). It can be done without R2 but that would put the meter in danger of having a high voltage across it.

R2 and R3 are two resistors in parallel and combined can be counted as a single 5MΩ resistor as shown in the first formula in the diagram. Together they’re usually labelled as R2||R3. The schematic on the right is a simplified way of looking at the circuit with R3 pulled out of the meter and combined with R2.

R1 and R2||R3 form a voltage divider. The second formula in the diagram shows how the voltage across R2||R3 is calculated. Notice that the result, 74.9V is almost 1/1000th of 75,000V, the voltage being measured. It’s only 0.1% off, which is smaller than the meter accuracy. That means we can say that to get the actual voltage you simply multiply the measured voltage by 1000 (75V x 1000 = 75,000V).

The value of R1 was selected so that it wouldn’t load down the circuit being measured. High voltage circuits often don’t have much spare current for measuring purposes. R1 was also selected such that there wouldn’t be a problem with leakage over its surface. In my case R1 is made up of 25 smaller resistors and so with the voltage divided among them, I figured there’d be no leakage problem. R1 was lastly selected so that R2||R3 would have a useful voltage range across it. 3000V is measured as 3V, 20,000V is measured as 20V, and 75,000V is measured as 75V, and so on, which are reasonable values for a meter.

DIY HV probe resistors waxed

For R1 I purchased 25 200MΩ high voltage resistors (MX440-200M, 1%, 11kV) from Caddock and connected them in series. In hindsight, I should have gone with higher resistance but longer resistors which would have made for a shorter probe.

The resistors were all soldered together with big, round solder bulbs to avoid sharp points which can cause losses due to ionization. Then each connection was encased in a mold and paraffin wax poured in to further minimize losses.

For added protection for the meter from high voltage I added two spark gaps inside in case some of the resistors shorted. The calculations for that are very involved so I won’t go through them here. From the photo you can see they consist of rounded solder bulbs, spaced a precise distance apart from the metal end caps of two resistors.

Conclusion

And that’s how I measure high voltage. I’d be very curious how you’ve done it, what probes you’d recommend and what your experience has been. Also, have you done any AC voltage measurements? That’s something I haven’t done. Measuring the voltage of a Tesla coil comes to mind. Let us know in the comments below.


Filed under: classic hacks, Engineering, Featured

This Old Mouse Keeps Track of Filament Usage

พฤ, 12/08/2016 - 19:01

Keeping track of your 3D-printer filament use can be both eye-opening and depressing. Knowing exactly how much material goes into a project can help you make build-versus-buy decisions, but it can also prove gut-wrenching when you see how much you just spent on that failed print. Stock filament counters aren’t always very accurate, but you can roll your own filament counter from an old mouse.

[Bin Sun]’s build is based around an old ball-type PS/2 mouse, the kind with the nice optical encoders. Mice of this vintage are getting harder to come by these days, but chances are you’ve got one lying around in a junk bin or can scrounge one up from a thrift store. Stripped down to its guts and held in place by a 3D-printed bracket, the roller that used to sense ball rotation bears on the filament on its way to the extruder. An Arduino keeps track of the pulses and totalizes the amount of filament used; the counter handily subtracts from the totals when the filament is retracted.

Simple, useful, and cheap — the very definition of a hack. And even if you don’t have a 3D-printer to keep track of, harvesting encoders from old mice is a nice trick to file away for a rainy day. Or you might prefer to just build your own encoders for your next project.


Filed under: 3d Printer hacks, Android Hacks