Getting Sparks from Water with Lord Kelvin’s Thunderstorm

In the comments to our recent article about Wimshurst machines, we saw that some hackers had never heard of them, reminding us that we all have different backgrounds and much to share. Well here’s one I’m guessing even fewer will have heard of. It’s never even shown up in a single Hackaday article, something that was also pointed out in a comment to that Wimshurst article. It is the Lord Kelvin’s Water Dropper aka Lord Kelvin’s Thunderstorm, invented in the 1860s by William Thomson, 1st Baron Kelvin, the same fellow for whom the Kelvin temperature scale is named.  It’s a device that produces a high voltage and sparks from falling drops of water.

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Saturday Clock: An 0.000011574Hz ATtiny85 clock

In these times when we try to squeeze out extra clock cycles by adding more cores to our CPUs and by enlisting the aid of GPUs, [Ido Gendel] thought it would be fun to go in the exact opposite direction, supply a clock to the ATtiny85 that cycles only once per day, or at 0.000011574Hz. What application could this have? Well, if he could do it in seven instructions or less, how about turning on an LED at sunset Friday evening, to indicate the start of the Jewish Shabbat (Saturday), and turn it off again at sunset Saturday evening.

Notice the subtlety. A clock that cycles once per day means you can execute at most one instruction per day. Luckily on AVR microcontrollers, the instructions he needed can execute in just one cycle. That of course meant diving down into assembly code. [Ido] wasn’t an assembly wizard, so to find the instructions, he compiled C code and examined the resulting assembly until he found what he needed. One instruction turns on the LED and the instruction immediately following turns it off again, which normally would make it happen too fast for the human eye to register. But the instruction to turn it on runs on Friday evening and the very next instruction, the one that turns it off, doesn’t run until Saturday evening. Do you feel like you’re in a science fiction story watching time slowed down? Freaky. A few NOPs and the jump for the loop take up the remaining five cycles for the week.

For the source of the clock he chose to use an LDR to detect when the light level dropped at the end of the day. The problem he immediately ran into was that clouds, bird shadows, and so on, also cause drops in the light level. The solution he found was to widen the light and dark range by adding a TLV3702 push-pull output comparator and some resistors. [Ido] gives a detailed explanation of the circuit in the video after the break.

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How Many Inventors Does It Take To Invent A Light Bulb

Many credit the invention of the incandescent light bulb with Edison or Swan but its development actually took place over two centuries and by the time Edison and Swan got involved, the tech was down to the details. Those details, however, meant the difference between a laboratory curiosity that lasted minutes before burning out, and something that could be sold to consumers and last for months. Here then is the story of how the incandescent light bulb was invented.

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Robot Ants Wear Circuitry as Exoskeleton

[FESTO] keeps coming up with new tricks that make us both envious and inspired. Take their bionicANTs for example. Watching a group of them cooperate to move objects around looks so real that you’re instantly reminded of the pests crawling across your floor, but looking at them up close they’re a treasure trove of ideas for your next robot project.

Ant exoskeleton as circuit board
Ant exoskeleton as circuit board

The exoskeleton is 3D printed but they then use the outer surface of that exoskeleton as a circuit board for much of the circuitry. The wiring is “painted on” using a 3D MID (Molded Interconnect Device) process. While FESTO didn’t give specifics about their process, a little research shows that 3D MID involves the 3D printed object being made of a special non-conductive metal material, a laser then “drawing” the traces in the material, and then dipping the object in various baths to apply copper, nickel and gold layers. We mortal hackers may not have the equipment for doing this ourselves in our workshops but seeing the beautiful result should be inspiration enough to get creative with our copper tape on the outer surfaces of our 3D printed, CNC’d, or hand-carved parts.

We also like how they took a the mouse sensor from under a regular computer mouse and attached it to the ant’s underside, pointing down for precision dead reckoning. For the legs they used three piezo bending transducers. However, these give a deflection of only 1.5mm in both directions, not enough for walking. They increase this to over 10mm with the addition of a plastic hinge, another idea to keep in mind when building that next tiny robot. And there are more ideas to be taken advantage of in their ants, which you can see being built in the video below.

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Automatic Deploying Lightning Rod

As hackers, hams, and builders of all sorts of things that go in our yards or are attached to our houses we often encounter resistance from building associations and by-laws regarding what to us are harmless necessities but to others are risks to their sight-lines, property values, or are seen as safety hazards. A student at the Bergen County Academies Mechatronics Research Lab has identified this same issue with lightning rods for homes, monuments, and buildings of fine architecture; people don’t want to add unsightly lightning rods despite their proven protections. Her solution? Detect when a storm is approaching and automatically deploy the lightning rod for the duration of the storm.

To detect the approaching storm she’s monitoring the changing barometric pressure using an Adafruit BMP085 barometric pressure, temperature and altitude sensor (now replaced by the BME280) connected to an Arduino with a motor shield. If the pressure is low and the trend has been decreasing then she pivots the lightning rod up using a motor salvaged from a satellite dish. When the risk abates, she pivots the rod back down again. Admittedly the lightning rod has yet to be attached and care will have to be taken with how the discharge cable is deployed but it’s a start. You can see it in action in the video below.

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Soda Bicarb Diode Steering Circuit For 7-Segment Display

[Hales] has been on a mission for a while to make his own diodes and put them to use and now he’s succeeded with diodes made of sodium bicarbonate and water, aluminum tape and soldered copper. By combining 49 of them he’s put together a soda bicarb diode steering circuit for a 7-segment display capable of showing the digits 0 to 9.

He takes the idea for his diode from electrolytic capacitors. A simple DIY electrolytic capacitor has an aluminum sheet immersed in a liquid electrolyte. The aluminum and the conductive electrolyte are the two capacitor plates. The dielectric is an aluminum oxide layer that forms on the aluminum when the correct polarity is applied, preventing current flow. But if you reverse polarity, that oxide layer breaks down and current flows. To [Hales] this sounded like it could also act as a diode and so he went to work doing plenty of experiments and refinements until he was confident he had something that worked fairly well.

In the end he came up with a diode that starts with a copper base covered in solder to protect the copper from his sodium bicarbonate and water electrolyte. A piece of aluminum tape goes on top of that but is electrically insulated from it. Then the electrolyte is dabbed on such that it’s partly on the solder and partly on the aluminum tape. The oxide forms between the electrolyte and the aluminum, providing the diode’s junction. Connections are made to the soldered copper and to the aluminum.

To truly try it out he put together a steering circuit for a seven segment display. For that he made a matrix of his diodes. The matrix has seven columns, one for each segment on the display. Then there are ten rows, one for each digit from 0 to 9. The number 1, for example, needs only two segments to light up, and so for the row representing 1, there are only two diodes, i.e. two dabs of electrolyte where the rows overlap the columns for the desired segments. The columns are permanently wired to their segments so the final connection need only be made by energizing the appropriate row of diodes. You can see [Hales] demonstrating this in the video below the break.

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Wimshurst Machines: High Voltage from the Gods

Wimshurst machine demo
Wimshurst machine demo

The Wimshurst machine is one of the oldest and best known electrostatic machines, consisting of its iconic two counter rotating disks and two Leyden jars. Most often you see someone hand cranking it, producing sparks, though we’ve seen it used for much more, including for powering a smoke precipitator for cleaning up smoke and even for powering a laser.

It works through an interesting sequence of events. Most explanations attempt to cram it all into one picture, requiring some major mental gymnastics to visualize. This often means people give up, resigned to assume these work through some mythical mechanics that defy a mortal’s ability to understand.

So instead, let’s do a step-by-step explanation.

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