Harley-Hardened Wire Helps High-Gain Antenna Hack

What does a Harley-Davidson motorcycle have to do with building antennas? Absolutely nothing, unless you happen to have one and need to work-harden copper wire to build a collinear antenna for LoRa.

We’ll explain. Never being one to settle, [Andreas Spiess] needed a better antenna for his LoRa experiments. Looking for high gain and an omnidirectional pattern, he bought a commercial colinear antenna, which is a wire with precisely spaced loops that acts like a stack of dipoles. Sadly, in a head-to-head test [Andreas] found that the commercial antenna was no better than lower gain antennas in terms of range, and so he decided to roll his own.

Copper wire is a great material for antennas since it can be easily formed without special tools and it solders like a champ. But the stuff you get at the home center is nowhere near stiff enough for a free-standing vertical whip. This is where the Harley came in: [Andreas] used his Hog to stretch out the 1.75-mm diameter (a little bigger than #14 AWG) copper wire. Not only did the work-hardening stiffen the wire, it reduced its diameter to the 1.4 mm needed for the antenna design. His vector network analyzer told him that ground-plane elements and a little fiddling with the loop diameter were needed to get the antenna to resonate at 868 MHz, but in the end it looks like the antenna is on track to deliver 5-dBi of gain.

Of course there are plenty of other ways to stretch out a wire — you could just stretch it out with hanging weights, or even with a go-kart motor-powered winch if you’re ambitious. But if you’ve got a bike like that, why not flaunt it?

Continue reading “Harley-Hardened Wire Helps High-Gain Antenna Hack”

FabricKeyboard Is Piano, Theremin And More

Two researchers of Responsive Environments, MIT Media Lab, have put to together a device that is an amazing array of musical instruments squeezed into one flexible package. Made using seven layers of fabrics with different electrical properties, the result can be played using touch, proximity, pressure, stretch, or with combinations of them. Using a fabric-based keyboard, ribbon-controller, and trackpad, it can be played as a one-octave keyboard, a theremin, and in ways that have no words, such as stretching while pressing keys. It can also be folded up and stuffed into a case along with your laptop, and care has even been taken to make it washable.

The FabricKeyboard layers
The FabricKeyboard layers

Layer one, the top layer, is a conductive fabric for detecting proximity and touch. The twelve keys can work independently with a MPR121 proximity touch controller or the controller can treat them all as one, extending the distance the hand can be and have it still work. Layer two is just a knit fabric but layers three to six detect pressure, consisting to two conductive layers with a mesh fabric and a piezo-resistive fabric in between. The piezo-resistive fabric is LTT-SPLA from eeonyx, a knit fabric coated with the conductive polymer, polypyrrole (PPy). Layer seven consists of two strips of knitted spandex fabric, also coated with PPy, and detects stretching. Two strips of this are sewn on the bottom, one horizontal and one vertical. You can see and hear the amazing sound this all produces in the video below.

Continue reading “FabricKeyboard Is Piano, Theremin And More”

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.

Continue reading “Resistance in Motion: What You Should Know About Variable Resistors”

Stretchable Traces for Flexible Circuits

Electronic components are getting smaller and smaller, but the printed circuit boards we usually mount them on haven’t changed much. Stiff glass-epoxy boards can be a limiting factor in designing for environments where flexibility is a requirement, but a new elastic substrate with stretchable conductive traces might be a game changer for wearable and even implantable circuits.

qxMo1DResearchers at the Center for Neuroprosthetics at the École Polytechnique Fédérale de Lausanne are in the business of engineering the interface between electronics and the human nervous system, and so have to overcome the mismatch between the hardware and wetware. To that end, [Prof. Dr. Stéphanie P. Lacour]’s lab has developed a way to apply a liquid metal to polymer substrates, with the resulting traces capable of stretching up to four times in length without cracking or breaking. They describe the metal as a partially liquid and partially solid alloy of gallium, with a gold added to prevent the alloy from beading up on the substrate. The applications are endless – wearable circuits, sensors, implantable electrostimulation, even microactuators.

Looks like progress with flexibles is starting to pick up, what with the conductive silicone and flexible phototransistors we’ve covered recently. We’re excited to see where work like this leads.

Continue reading “Stretchable Traces for Flexible Circuits”

Stretch-bike

This long bike is built for haulin’. After needing to find a truck to transport his welding equipment (ironically in order to build another bike) [Nick Johnson] decided it was time to make a two-wheeled cargo transport. He extended the frame in order to add a cradle in the front. Eventually there will be sides on that box but for now it works like a charm for transporting his groceries. With the long wheel-base this should be pretty stable as long as you balance your cargo. We’d certainly be more apt to try a ride on this rather than the double-decker death-trap from a few weeks ago.

Make a stretchy fabric USB cable

Stretchy fabric USB cable
If you’ve been puzzled over a discreet, durable way to sew wiring into your clothing, then puzzle no more: [Plusea] has put together a writeup detailing how to make a USB cable partly out of stretchy cotton fabric. Although the design as detailed doesn’t give much practical use for the invention, we can think of several very effective ways of exploiting this toy. Imagine, for example, placing a USB battery pack into one pocket of a jacket, a portable digital audio recorder in the other, and a lavalier microphone in the lining, thus enabling dozens of hours of covert audio surveillance.