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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Amazing Carbon Foam Doesn’t Take Much Bread

A lot of people knew the Space Shuttle had ceramic tiles to protect its nose from reentry heat. That’s mostly because the tiles fell off a lot and each one was a unique shape, so it got a lot of press coverage. However, you didn’t hear as much about the parts of the orbiter that got really hot: the forward part of the wings and the tip of the nose. For those, NASA used an exotic material called RCC or reinforced carbon-carbon. Other uses include missile nose cones and Formula One brakes. A similar material, carbon fiber-reinforced silicon carbide appears in some high-end car brakes. These materials can take high temperatures, easily.

[AvE] wanted to make some carbon foam for experiments. It does take a little bread, though. Not money, but literal bread. To create the foam, he burns bread slices in a chamber full of argon. The stuff has some amazing properties.

In the video below, you can see the foam protecting a thermocouple from a torch flame and even holding melting aluminum. Not bad for a few pieces of bread.

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Forget Stopping Bullets – Vest Warms You While Stopping Taser


[Bruce Wayne] [Shenzhen] wanted a garment that would protect him from a jolt, while keeping him toasty in the cold weather. Well that’s not it at all, these are merely two of his projects using the same material in different ways.

We’re going to start with the infrared image on the right. This is a vest with chest and back pieces made of carbon tape totaling two meters of the material swirled on each side. Hook it to a power source and the carbon tape warms the wearer. Portability is something of an issue as each “element” takes 36 W of power (3A at 12V). Click through for advice on how to interface the tape with the power source.

Onto the main event… avoiding electrical shock when you get all up in the grill of that mall cop you’re hated for years. [Shenzhen’s] jacket is really just an ordinary long-sleeved coat. But he separated the lining at the bottom seam and used fusible material to hold the carbon tape in place. The carbon tape provides a better conductor than your skin, preventing the shock from stunning you as it was intended. This really is the thing of superheroes, or former editors who should have known better.

Paper accelerometers for pennies in the works

Cheap paper accelerometers? Put us down for a dozen to start. They’re not quite ready for mass production yet but it looks like they’re on the way.

[George Whitesides] led a team to develop the new technology that uses simple manufacturing methods to produce the sensor seen above. Graphite and silver inks were screen printed onto heavy paper. The single limb sticking out from the body of the sensor is a separate piece of paper that bends the carbon area when force is applied. This changes the carbon’s resistance which is measured using a Wheatstone bridge constructed by gluing resistors to the device.

It sounds unsophisticated compared to most of the accelerometer modules we’re used to, but if you need a sensor that detects sudden motion this sounds like the perfect part. Now who wants to be the first person to replicate this in their basement?

[Thanks Fabien]