Fifty Shades Of Gray Code

January 25, 2017 by Al Williams 77 Comments

Some years back, a museum asked me to help them with an exhibit a contractor had built for them. It was a wheel like the one on Wheel of Fortune, but smaller and mounted on the wall instead of the floor. You would spin the wheel, it would stop on some item, and a computer would play a short video about the item. Physically and mechanically, it was a beautifully built exhibit. The electronics, though, left something to be desired.

In principle, this is pretty simple computer task. Measure the position of the wheel, and when it stops moving, play a video based on the position. The problem was the folks who created the artistic mechanics didn’t think hard about the electronics behind it. Sometimes–but not often–the wheel would play the wrong video. Sometimes it wouldn’t play at all.

The Prime Suspect

My immediate suspicion turned out to be correct. I took the wheel off its mount to discover copper foil tape on the back of it. Each pie wedge had foil in different areas and there were two brushes in each area. When the wheel stopped, two of the brushes would be shorted together and the rest were open. The way they detected that was bizarre, but that wasn’t the problem. (It involved a cannibalized PS/2 keyboard.)
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The Birth Of Quantum Electrodynamics

January 24, 2017 by Will Sweatman 39 Comments

The start of World War II threw quantum theory research into disarray. Many of the European physicists left Europe all together, and research moved across the ocean to the shores of the United States. The advent of the atomic bomb thrust American physicists into the spotlight, and physicists began to meet on Shelter Island to discuss the future of quantum theory. By this time one thing was certain: the Copenhagen interpretation of quantum theory had triumphed and challenges to it had mostly died off.

This allowed physicists to focus on a different kind of problem. At this point in time quantum theory was not able to deal with transitional states of particles when they are created and destroyed. It was well known that when an electron came into contact with a positron, the two particles were destroyed and formed at least two photons with a very high energy, known as gamma rays. On the flip side, gamma ray photons could spontaneously turn into positron-electron pairs.

No one could explain why this occurred. It had become obvious to the physicists of the day that a quantum version of Maxwell’s electromagnetic field theory was needed to explain the phenomenon. This would eventually give rise to QED, short for quantum electrodynamics. This is a severely condensed story of how that happened.

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Relay Computing

January 19, 2017 by Al Williams 25 Comments

Recently, [Manuel] did a post on making logic gates out of anything. He mentioned a site about relay logic. While it is true that you can build logic gates using switch logic (that is, two switches in series are an AND gate and two in parallel are an OR gate), it isn’t the only way. If you are wiring a large circuit, there’s some benefit to having regular modules. A lot of computers based on discrete switching elements worked this way: you had a PCB that contained some number of a basic gate (say, a two input NAND gate) and then the logic was all in how you wired them together. And in this context, the SPDT relay was used as a two input multiplexer (or mux).

In case you think the relay should be relegated to the historical curiosity bin, you should know there are still applications where they are the best tool for the job. If you’re not convinced by normal macroscopic relays, there is some work going on to make microscopic relays in ICs. And even if they don’t use relays to do it, some FPGAs use mux-based logic inside. So it’s worth your time to dig into the past and see how simply switching between two connections can make a computer.

Mux Mania

How do you go from a two input mux to an arbitrary logic gate? Simple, if you paid attention to the banner image. (Or try it interactive). The mux symbols show the inputs to the left, the output to the right and the select input at the bottom. If the select is zero, the “0” input becomes the output. If the select is one, the “1” input routes to the output.

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Will Supercapacitors Ever Replace Batteries?

January 19, 2017 by Manuel Rodriguez-Achach 124 Comments

Recharging your mobile phone or your electric vehicle in a few minutes sure sounds appealing. Supercapacitor technology has the potential to deliver that kind of performance that batteries currently can’t, and while batteries are constantly improving, the pace of development is not very fast. Just remember your old Nokia mobile with Ni-Cad batteries and several days of usage before a recharge was needed. Today we have Lithium-Ion batteries and we have to charge our phones every single day. A better energy storage option is clearly needed, and supercapacitors seem to be the only technology that is close to replace the battery.

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Understanding The Quartz Crystal Resonator

January 17, 2017 by Jenny List 68 Comments

Accurate timing is one of the most basic requirements for so much of the technology we take for granted, yet how many of us pause to consider the component that enables us to have it? The quartz crystal is our go-to standard when we need an affordable, known, and stable clock frequency for our microprocessors and other digital circuits. Perhaps it’s time we took a closer look at it.

The first electronic oscillators at radio frequencies relied on the electrical properties of tuned circuits featuring inductors and capacitors to keep them on-frequency. Tuned circuits are cheap and easy to produce, however their frequency stability is extremely affected by external factors such as temperature and vibration. Thus an RF oscillator using a tuned circuit can drift by many kHz over the period of its operation, and its timing can not be relied upon. Long before accurate timing was needed for computers, the radio transmitters of the 1920s and 1930s needed to stay on frequency, and considerable effort had to be maintained to keep a tuned-circuit transmitter on-target. The quartz crystal was waiting to swoop in and save us this effort.

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The Electrical Grid Demystified

January 17, 2017 by Bryan Cockfield 80 Comments

Our society needs energy, and lots of it. If you’re reading this then the odds are astronomically good that you’re on a computer somewhere using energy, with the power cord plugged into the mysterious “black box” that is the electrical grid. The same is true if you’re reading this on a laptop or phone, which was charged from said black box even though it may not be connected at this moment. No matter where you are, you’re connected to some sort of energy source almost all the time. For almost every one of us, we have power lines leading up to our homes, which presumably connect to a power plant somewhere. This network of power lines, substations, even more power lines, and power plants is colloquially known as the electrical grid which we will be exploring in a series of articles.

While the electrical grid is a little over a century old, humanity has been using various energy sources since the agricultural revolution at least. While it started with animal fat for candles, wind for milling grain, and forests for building civilizations, it moved on to coal and steam during the industrial revolution and has ended up in a huge interconnected network of power lines connected to nuclear, natural gas, coal, solar, and wind sites around the world. Regardless of the energy source, though, there’s one reason that we settled on using electricity as the medium for transporting energy: it’s the easiest way we’ve found to move it from place to place.

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Pulsed Power And Its Applications

January 11, 2017 by Manuel Rodriguez-Achach 43 Comments

Pulsed power is a technology that consists in accumulating energy over some period of time, then releasing it very quickly. Since power equals energy (or work) divided by time, the idea is to emit a constant amount of energy in as short a time as possible. It will only last for a fraction of a second though, but that instantaneous power has very interesting applications. With this technology, power levels of more than 300 terawatts have been obtained. Is this technology for unlimited budgets, or is this in reach of the common hacker?

Consider for example discharging a capacitor. A large 450 V, 3300 uF electrolytic capacitor discharges in about 0.1 seconds (varies a lot depending on capacitor design). Since the energy stored in it is given by 1/2 CV², which gives 334 Joules of energy, the power delivered will be 3340 watts. In fact a popular hacker project is to build large capacitor banks. Once you have the bank, and a way to charge it, you can use it to power very interesting devices such as:

untitled1 — A portable, 1.25 kJ coilgun by [Jason Murray]

Railguns in particular are subject to serious research. You may have read about the navy railgun, capable of reaching a muzzle speed of more than 4,600 mph (around Mach 6), more than any other explosive-powered gun. Power is provided by a 9-megajoule capacitor bank. The capacitors discharge on two conducting rails, generating an electromagnetic field that fires the projectile along the rails. The rail wear due to the tremendous pressures and currents, in the millions of amperes range, is still a problem to be solved.

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