Building a keyboard isn’t a big project these days. Controller chips and boards are readily available, switches are easy to find, and a 3D printer can do a lot of what used to be the hard parts. But engineers at Purdue have printed a self-powered Bluetooth keyboard on an ordinary sheet of paper. You can see videos of the keyboards at work below.
The keyboards work by coating paper with a highly fluorinated coating that repels water, oil, and dust. Special inks print triboelectric circuits so that pressing your finger on a particular part of the paper generates electricity. We were skeptical that the Bluetooth part is self-powered, although maybe it is possible if you have some very low-power electronics or you manage the power generated very carefully.
[Mr. Carlson]’s shocking tale began with a quiet evening in his jam-packed lab as a snowstorm raged outside. He heard a rhythmic clicking coming from the speakers of his computer, even with the power off. Other speakers in the lab were getting into the act, as was an old radio receiver he had on the bench. The radio, which was connected to an outdoor antenna by a piece of coax, was arcing from a coil to the chassis in the front end of the radio. The voltage was enough to create arcs a couple of millimeters long and bright blue-white, with enough current to give [Mr. Carlson] a good bite when he touched the coax. The discharges were also sufficient to destroy an LED light bulb in a lamp that was powered off but whose power cord was unlucky enough to cross the antenna feedline.
Strangely, the coil from which the arc sprang formed a 36-ohm shunt to the radio’s chassis, giving the current an apparently easy path to ground. But it somehow found a way around that, and still managed to do no damage to the sturdy old radio in the process. [Mr. Carlson] doesn’t offer much speculation as to the cause of the phenomenon, but the triboelectric effect seems a likely suspect. Whatever it is, he has set a trap for it, to capture better footage and take measurements should it happen again. And since it’s the Great White North, chances are good we’ll see a follow-up sometime soon.
Serpentine is a gesture sensor that’s the equivalent of a membrane potentiometer, flex and stretch sensor, and more. It’s self-powering and can be used in wearable hacks such as the necklace shown in the banner image though we’re thinking more along the lines of the lanyard for Hackaday conference badges, adding one more level of hackability. It’s a great way to send signals without anyone else knowing you’re doing it and it’s easy to make.
Serpentine is the core of a research project by a group of researchers including [fereshteh] of Georgia Tech, Atlanta. The sensor is a tube made of a silicone rubber and PDMS (a silicone elastomer) core with a copper coil wrapped around it, followed by more of the silicone mix, a coil of silver-coated nylon thread, and a final layer of the silicone mix. Full instructions for making it are on their Hackaday.io page.
There are three general interactions you can have with the tube-shaped sensor: radial, longitudinal, and tangential. Doing various combinations of these three results in a surprising variety of gestures such as tap, press, slide, twist, stretch, bend, and rotate. Those gestures result in signals across the copper and silver-coated nylon electrodes. The signals pass through an amplifier circuit which uses WiFi to send them on to a laptop where signal processing distinguishes between the gestures. It recognizes the different ones with around 90% accuracy. The video below demonstrates the training step followed by testing.
Our Hackaday Prize Challenges are evaluated by a panel of judges who examine every entry to see how they fare against judging criteria. With prize money at stake, it makes sense we want to make sure it is done right. But we also have our Hackaday Prize achievements, with less at stake leading to a more free-wheeling way to recognize projects that catch our eye. Most of the achievements center around fun topics that aren’t related to any particular challenge, but it’s a little different for the Infinite Improbability achievement. This achievement was unlocked by any project that impressed with their quest for power, leading to some overlap with the just-concluded Power Harvesting Challenge. In fact, when the twenty Power Harvesting winners were announced, we saw that fourteen of them had already unlocked the achievement.
Each of the Power Harvesting winners will get their own spotlight story. And since many of them have unlocked this achievement, now is the perfect time to take a quick tour through a few of the other entries that have also unlocked the Infinite Improbability achievement.
What I particularly like about the Van de Graaff (or VDG) is that it’s a combination of a few discrete scientific principles and some mechanically produced current, making it an interesting study. For example, did you know that its voltage is limited mostly by the diameter and curvature of the dome? That’s why a handheld one is harmless but you want to avoid getting zapped by one with a 15″ diameter dome. What follows is a journey through the workings of this interesting high voltage generator.
In high voltage applications involving tens of thousands of volts, too often people think about the high voltage needed but don’t consider the current. This is especially so when part of the circuit that the charge travels through is an air gap, and the charge is in the form of ions. That’s a far cry from electrons flowing in copper wire or moving through resistors.
Consider the lifter. The lifter is a fun, lightweight flying machine. It consists of a thin wire and an aluminum foil skirt separated by an air gap. Apply 25kV volts across that air gap and it lifts into the air.
Lifter flying with high voltage power supply
So you’d think that the small handheld Van de Graaff generator pictured below, that’s capable of 80kV, could power the lifter. However, like many high voltage applications, the lifter works by ionizing air, in this case ionizing air surrounding the thin wire resulting in a bluish corona. That sets off a chain of events that produces a downward flowing jet of air, commonly called ion wind, lifting the lifter upward.
Having hacked away with high voltage for many years I’ve ended up using a large number of very different high voltage sources. I say sources and not power supplies because I’ve even powered a corona motor by rubbing a PVC pipe with a cotton cloth, making use of the triboelectric effect. But while the voltage from that is high, the current is too low for producing the necessary ion wind to make a lifter fly up off a tabletop. For that I use a flyback transformer and Cockcroft-Walton voltage multiplier power supply that’s plugged into a wall socket.
So yes, I have an unorthodox skillset when it comes to sourcing high voltage. It’s time I sat down and listed most of the power sources I’ve used over the years, including a bit about how they work, what their output is like and what they can be used for, as well as some idea of cost or ease of making. The order is from least powerful to most powerful so keep reading for the ones that really bite.
You’ve no doubt encountered this effect. It’s how your body is charged when you rub your feet on carpet and then get a shock from touching a door knob. When you rub two specific materials together there’s a transfer of electrons from one to the other. Not just any two materials will work. To find out which materials are good to use, have a look at a triboelectric series table.
Materials that are on the positive end of the table will become positively charged when rubbed against materials on the negative end of the table. Those materials will become negatively charged. The further apart they are in the table, the stronger the charging.