Resistance in Motion: What You Should Know About Variable Resistors

Adjusting the volume dial on a sound system, sensing your finger position on a touch screen, and knowing when someone’s in the car are just a few examples of where you encounter variable resistors in everyday life. The ability to change resistance means the ability to interact, and that’s why variable resistance devices are found in so many things.

The principles are the same, but there are so many ways to split a volt. Let’s take a look at what goes into rotary pots, rheostats, membrane potentiometers, resistive touchscreens, force sensitive resistors, as well as flex and stretch sensors.

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What is There to Know About Resistors?

Resistor: A passive chunk of material that resists the flow of electrical current. A terminal is connected to each end you’re done. What could be simpler?

It turns out it’s not so simple at all. Temperature, capacitance, inductance and other factors all play a part in making the resistor a rather complex component after all. Even its uses in circuits are many, but here we’ll just focus on the different types of fixed-value resistors, how they’re made, and what makes them desirable for different applications.

Let’s start with a simple one, and one of the oldest.

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Hackaday Links: January 3, 2016

Cx5 is a strange material that’s a favorite of model makers and prop replicators. It’s kind of like a wax, kind of like a clay, and a little bit like a plastic. Now it’s a 3D printer filament. It looks very interesting for sculpted and highly detailed models, something the 3D printing scene hasn’t had yet.

So you want a CNC machine, right? Tormach makes a good one, and here’s what it takes to put a PCNC440 in your garage. This is an incredible amount of work and a great excuse to buy an engine hoist.

[Zemnmez] could find dozens of apps and webpages that would calculate resistor color codes for him automatically. What he couldn’t find is one that would do it in reverse – i.e. type in a resistor value and return the correct color code. He made this.

[aggaz] needed a way to connect multiple MIDI devices to his computer. The MIDI spec provides a neat piece of hardware for just this occasion – the MIDI thru box. The only thing you need to build a single MIDI thru box is an opto-isolator and a buffer. It’s easy enough to build, although the DIN5 jacks used for MIDI devices are pretty expensive nowadays. (FWIW- We get an invalid certificate error when loading this page but you should still be able to load it.)

AliExpress always has some interesting stuff on it, and [Ethan] found something very cool. They’re A8 CPUs found in the latest iPhone. Are they real? Who knows. I bought one, and you’re going to get pictures in another links post in a month or so.

The Game Boy Micro was released by Nintendo in 2005 and quickly became one of the coolest and most desired handheld consoles on the planet. You need only look at the eBay listings for the Micro as evidence of its desirability. [ModPurist] took an old DS Lite and converted it into a Game Boy Micro – same idea, larger package.

Hackaday Links: July 12, 2015

Adafruit is working on a series of videos that’s basically Sesame Street for electronics. G is for Ground is out, where [Adabot] discovers pipes and lightning rods are connected to ground. Oh, the rhyming. Here’s the rest of the videos so far. We can’t wait for ‘Q is for Reactive Power’.

Think you’re good enough to build an airlock 70 cubic meters in volume that can cycle once every thirty seconds? How about building a 500 mile long steel tube with zero expansion joints across active fault lines? Can you stop a 3 ton vehicle traveling at 700 miles per hour in fifteen seconds? These are the near-impossible engineering challenges demanded of the hyperloop. The fact that no company will pay for this R&D should tell you something, but that doesn’t mean you still can’t contribute.

Calling everyone that isn’t from away. [Paul] lives near Augusta, Maine and can’t find a hackerspace. Augusta is the capital of the state, so there should be a hackerspace nearby. If you’re in the area, go leave a message on his profile.

Last week we found memristors you can buy. A few years ago, [Nyle] found them while hiking. They were crudded up shell casings, and experiments with sulfur and copper produced a memristor-like trace on a curve tracer.

Need a way to organize resistors? Use plastic bags that are the same size as trading cards.

The Arduino is too easy. It must be packaged into a format that is impossible to breadboard. It should be shaped like a banana. Open source? Don’t need that. The pins are incorrectly labelled, and will be different between manufacturing runs.

New Part Day: Memristors

For the last few years, the people in the know have been wondering about the memristor. The simplest explanation of what a memristor is comes from the name itself – it’s a memory resistor. In practice it’s a little more complex, but this basic understanding is enough to convey the fact that it’s a resistor that changes its resistance based on how much current has gone through it. The memristor was first described in the 70s by [Leon Chua], the idea sat in journals for nearly forty years, and in 2008 a working memristor was created by HP Labs.

Now you can buy one. Actually, you can buy eight in a 16-pin DIP package. It will, reportedly, cost $240 for the 16-pin DIP. That’s only $30 per memristor, and it’s the first time you can buy them.

These memristors are based on a silver chalcogenide (Ge2Se3). When a circuit ‘writes’ to this memristor and applies a positive voltage, silver ion migrate to the chalcogenide, forming what the datasheet (PDF) calls dendrites. This lowers the resistance of the memristor. When a negative voltage is applied to the device, these dendrites are removed, the memristor is ‘erased’, and the memristor returns to a high-resistance state.

This silver chalcogenide memristor is different from the titanium oxide memristors developed by HP Labs that is most frequently cited when it comes to this forgotten circuit element. This work is from [Kristy Campbell] of Boise State University. She’s been working on it for more than a decade now, with IEEE publications, conference proceedings (that one’s full text), and dozens of patents.

As far as applications for memristors go, there are generally two schools of thought on that. The most interesting, in terms of current computer technology, is storage. Memristors can hold either a binary 0 or a 1 in a fraction of the space NAND Flash or old-fashioned magnetic hard drives ever will. That means greater storage density, and bigger capacity hard drives with lower power requirements. These memristors have a limit of how many times they can be cycled – ‘greater than 2000 times’ according to the datasheet. That’s nearly an order of magnitude less than MLC Flash, and something wear leveling can’t reasonably compensate for. This is a new technology, though, so that could change.

The second major expected use for memristors is neural nets. Neural nets are just a series of inputs, a few neurons, outputs, and connections between all three. These connections are weighted, and the variable resistance of memristors puts them in a unique position to emulate in hardware at the most basic level what was once done with software and custom ASICs. The trade name for these memristors – Neuro-Bit – and the company name – Bio Inspired Technologies – give you a clue at what the intended use is.

As with all new technologies, there’s always something that is inevitably created that was never imagined by the original designers. What these new applications are is at this point just speculation. Now that anyone can buy one of these neat new chips, it’s going to be interesting to see what can be made with these parts.

Hackaday Links: May 24, 2015

A few months ago, we heard about a random guy finding injection molds for old Commodore computers. He did what the best of us would do and started a Kickstarter to remanufacture these cool old cases. It’s the best story on retrocomputing this year, and someone else figured out they could remanufacture Commodore 64 keycaps. If you got one of these remanufactured cases, give the keycaps a look.

Remember this Android app that will tell you the value of resistors by reading their color code. Another option for the iOS crowd was presented at Maker Faire last weekend. It’s called ResistorVision, and it’s perfect for the colorblind people out there. An Android version of ResistorVision will be released sometime in the near future.

A few folks at Langly Research Center have a very cool job. They built a hybrid electric tilt wing plane with eight motors on the wing and two on the tail. It’s ultimately powered by two 8 hp diesel engines that charge Liion batteries. When it comes to hydrocarbon-powered hovering behemoths, our heart is with Goliath.

A bottom-of-the-line avionics panel for a small private plane costs about $10,000. How do you reduce the cost? Getting rid of FAA certification? Yeah. And by putting a Raspberry Pi in it. It was expoed last month at the Sun ‘N Fun in Florida, and it’s exactly what the pilots out there would expect: a flight system running on a Raspberry Pi. It was installed in a Zenith 750, a 2-seat LSA, registered as an experimental. You can put just about anything in the cabin of one of these, and the FAA is okay with it. If it’ll ever be certified is anyone’s guess.

Reading Resistors With OpenCV

Here’s a tip from a wizened engineer I’ve heard several times. If you’re poking around a circuit that has failed, look at the resistor color codes. Sometimes, if a resistor overheats, the color code bands will change color – orange to brown, blue to black, and so forth. If you know your preferred numbers for resistors, you might find a resistor with a value that isn’t made. This is where the circuit was overheating, and you’re probably very close to discovering the problem.

The problem with this technique is that you have to look at and decode all the resistors. If automation and computer vision is more your thing, [Parth] made an Android app that will automatically tell you the value of a resistor by pointing a camera at it.

The code uses OpenCV to scan a small line of pixels in the middle of the screen. Colors are extracted from this, and the value of the resistor is displayed on the screen. It’s perfect for scanning through a few hundred through hole resistors, if you don’t want to learn the politically correct mnemonic they’re teaching these days.

Video below, and the app is available for free on the Google Play store.

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