Homemade High Voltage Caps

Do you happen to have any 15,000 volt capacitors sitting around? [Ludic Science] didn’t so he did the next best thing. He built some.

If you understand the physics behind a capacitor (two parallel conductors separated by a dielectric) you won’t find the build process very surprising. [Ludic] uses transparency film as an insulator and aluminum foil for the conductive plates. Then he wraps them into a tube. He did throw in a few interesting tips about keeping the sheets smooth and how to attach the wires to the foil. The brown paper wrapper reminded us of old caps you might find in an antique radio.

The best part by far, though, was the demonstration of drawing an arc from a high voltage power supply with and without the capacitor in the circuit. As you might expect, playing with a few thousand volts charged into a capacitor requires a certain amount of caution, so be careful!

[Ludic] measured the capacitance value with a standard meter, but it wasn’t clear where the 15,000 volt rating came from. Maybe it was the power supply he used in the video and the capacitor could actually go higher.

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I am a Battery: Harvesting Heat Energy

If you get tired of charging batteries, you might be interested in [Hackarobot’s] energy harvesting demo. He uses a peltier device (although he’s really using it as a thermocouple which it is). A 1 farad super capacitor stores energy and an LTC3108 ultra low voltage converter with a 1:100 ratio transformer handles the conversion to a useful voltage.

The truth is, the amount of energy harvested is probably pretty small–he didn’t really characterize it other than to light an LED. In addition, we wondered if a proper thermocouple would work better (some old Russian radios used thermocouples either in fireplaces or kerosene lamps to avoid requiring batteries). Although a Peltier device and a thermocouple both use the Seebeck effect, they are optimized for different purposes. Thermocouples generate voltage from a temperature differential and Peltier modules generate temperature differentials from voltage.

However, as [Hackarobot] points out, the same technique might be useful with other alternate power sources like solar cells or other small generators. The module used has selectable output voltages ranging from 2.35V to 5V.

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Everything You Wanted to Know About Oscillators

Ever wonder how a crystal oscillator works? How does that little metal can with a sliver of quartz start vibrating to produce a clock signal for just about everything we use, while doing it in the accuracy range in the parts per million and cost practically nothing?

Well [Craig] decided its about time for an in depth tutorial  that covers everything you need to know to understand, design, and construct your very own. Wrapped up in a 41 minute video, [Craig]  covers the absolute basic theories and designs, math, datasheet explanation of crystals, and even a practical example of a Pierce crystal oscillator, suitable for use in a HF transceiver. Now you can make your own for your own application no matter if you’re just trying to save a pin on your favorite micro, or making a radio transceiver.

With this wealth of knowledge, whether you are learning for the first time, or just need a refresher, you should join us after the break, kick back and check out this highly informative video.

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Hacker Creates Thermal Probes by Welding with a PC Power Supply

[Illya Tsemenko] decided to build his own thermocouples from bare wire. [Illya] is interested in measuring the temperature of Liquid Nitrogen and for this he needed T-type probes. While you can buy these for about 20 bucks, he felt this was too expensive for what is essentially two pieces of wire and decided to build his own.

Thermocouples use the Seebeck effect, when a piece of metal is hot at one end, and cold at the other the electrons in the hot end will be more energetic and migrate towards the cold end, creating a voltage. While this migration occurs in single metal, it can’t easily be measured (as the voltage will be the same as the measurement point). For that reason thermocouples use two metals in which the migration occurs at different rates. This difference creates an overall migration in one direction, and a voltage can be measured which correlates to the temperature where the metals meet. Thermocouples are extremely common and have many applications.

In order to make his thermocouples [Illya] needed to weld the two metals together, and knocked together a quick welding rig using a PC power supply and graphite electrode from a powertool. The graphite electrode is important as it prevents oxidization during the welding process.

The process worked well, and [Illya] was able to make both K and T-type thermocouples and successfully measure temperatures down to -190 degrees C. Awesome work [Illya]!

DIY Punch Card System Despite Hanging Chads

Sometimes you just have parts lying around and want to make something out of them. [Tymkrs] had a robot paper cutter, so naturally they made punch cards. But then, of course, they needed a punch card reader, so they made one of those too. All with stuff lying around the shop.

The Silhouette Portrait paper cutter is meant for scrapbooking, but what evokes memories of the past more than punchcards? To cut out their data, rather than cute kittens or flowers, they wrote some custom code to turn ASCII characters into rows of dots. And the cards are done — you just have to clean up the holes that didn’t completely cut. These are infamously known as hanging chads.

The reader is made up of a block of wood, with a gap for the cards and perpendicular holes drilled for LEDs and photoresistors. This is cabled to a Propeller dev board with some simple firmware. We would have used photodiodes or phototransistors, because that’s what’s in our junk box (and because they have faster reaction time), but when you’ve got lemons, make lemonade.

OK, now that you’ve got a punch card reader and writer, what do you do with it? Password storage comes to mind.

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The Simplest Steam Engine

[RimstarOrg] has posted an awesome writeup on his Hero’s steam engine . Hero’s engine is a Greek design from the first century and is the earliest known steam engine. It’s amazing to think he developed the engine seventeen centuries before the industrial revolution, and yet it was largely ignored. While you can find more faithful replicas, of this landmark machine [RimstarOrg]’s rig can’t be beaten for simplicity and he does a great job of explaining the principal of operation and construction.

Using a soda can filled with water and a propane torch [RimstarOrg] was able to get the can to rotate rapidly by ejecting steam from two holes in the side of the can. A fishing swivel is used to provide a pivoting joint and allow the can to rotate freely.

While we’ve covered steam engines before, we loved this simple design, and can’t wait to see what [RimStarOrg] comes up with next.

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Hackers Measure Cable Lengths with Time Domain Reflectometers

[android] has built up a fast edge pulse generator for time domain reflectometry (TDR). TDR is a neat technique which lets you measure cable lengths using electrical signals and can also be used to locate faults within the cable.

TDR works by sending a pulse down the cable. When the pulse reaches the end of the unterminated cable it is reflected back to the source. By monitoring the delay between the original pulse and its reflection you can determine the length of the cable. We’ve seen projects that use TDR before, and it’s often used in telecoms industry to locate faults in long cable runs.

You can try TDR in your lab using only a scope to observe the delay and a function generator to create the pulse. However, the technique works a lot better with pulses that have very fast rise times. So [android] built a fast edge pulse generator based on [w2aew]s design. Then added googly eyes for good measure. His build works great and is a nice demonstration of the technique.