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
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
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
The Teclast X98 Pro is a tablet with a 9.7 inch, 2048 x 1536 pixel IPS display, 4GB of RAM, and 64GB of storage.
It’s also a dual OS tablet that runs Windows 10 and Google Android software. And it was one of Teclast’s first tablets to ship with an Intel Atom x5-Z8500 Cherry Trail processor when the Teclast X98 Pro launched in 2015.
So I reached out to the folks at Geekbuying to ask for a demo unit… and then I never got around to posting a review.
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
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
A week after acknowledging a serious security vulnerability affecting its software, the makers of AirDroid have released an updated version of their app for sharing data between an Android phone and a PC.
AirDroid 220.127.116.11 is said to fix the security problems that could have allowed malicious hackers to intercept data sent between your devices if you were using an unsecured WiFi network.
The latest version of AirDroid is available from the Google Play Store.
Oona Räisänen from Absorptions wrote an article about experimenting with CTCSS fingerprinting:
Identifying unknown radio transmitters by their signals is called radio fingerprinting. It is usually based on rise-time signatures, i.e. characteristic differences in how the transmitter frequency fluctuates at carrier power-up. Here, instead, I investigate the fingerprintability of another feature in hand-held FM transceivers, known as CTCSS or Continuous Tone-Coded Squelch System.
More details at Absorptions site.
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.
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.
- 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
Every Friday we give away some extra PCBs via Facebook. This post was announced on Facebook, and on Monday we’ll send coupon codes to two random commenters. The coupon code usually go to Facebook ‘Other’ Messages Folder . More PCBs via Twitter on Tuesday and the blog every Sunday. Don’t forget there’s free PCBs three times every week:
- Free PCB Sunday. The classic. Every week, get free PCBs right here on the blog comments
- Tweet-a-PCB Tuesday. Follow us and get boards in 144 characters or less
- Facebook PCB Friday. Free PCBs while you wait for the weekend
- Check out our video on how we mail PCBs worldwide.
- Yes, we’ll mail it anywhere in the world!
- We’ll contact you via Facebook with a coupon code for the PCB drawer.
- Limit one PCB per address per month, please.
- Like everything else on this site, PCBs are offered without warranty.
Microsoft is offering some seriously cheap tablets today, but those aren’t the only savings you’ll find in the Microsoft Store and Windows Store at the moment.
The company is also running a “free music Friday” promotion, where you can pick up 5 albums for free. Add the items to your account and you can stream them in Microsoft’s Groove Music app… but you can also download the music as DRM-free MP3 files that you can transfer to any device for listening on the go.
Michael from Acidbourbon writes:
This article covers the attempt to build a digital logarithmic potentiometer out of two linear potentiometers. The benefits of this concept
- Linear digital potentiometers can be easily procured and don’t cost much
- There are IC packages with two or four modules inside anyway
- The resulting logarithmic potentiometer is very flexible in terms of number of steps and steepness of the attenuation function
Full details at Acidbourbon homepage.
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.
Filed under: radio hacks
If you bought a Galaxy Note 7 smartphone and haven’t returned it yet… you really should. Not only is the phone prone to catching fire, subject to a massive recall, and barred from boarding airplanes with you, but soon you may not even be able to turn the thing on.
The Verge reports that Samsung and US wireless carriers may be planning to issue a software update next week that will stop the phone from charging.
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
Chinese chip maker Rockchip has two new processors on the way and they’r eboth designed for Android-based TV boxes.
The Rockchip RK3228H and RK3228B chips can both handle 4K video playback and H.24/H.265 video decoding. And they’re both expected to show up in Chinese OTT (Over the Top) and IPTV (Internet Protocol Television) devices.
We may also see them show up soon in some of the cheap Android-powered media players that have been coming out of China for the past few years.
Remember when Windows tablets used to be more expensive than their Android counterparts? Today you can pick up a model with an 8 inch, 1920 x 1080 pixel display, 2GB of RAM, 32GB of storage, and a quad-core processor for just $49.
The Microsoft Store is offering a 1-day sale on Windows tablets, and that includes a NuVision 8 inch tablet with an Atom Z3735F Bay Trail processor for $49.
Want something with a newer/faster processor?
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
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
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