Retrotechtacular: Understanding a voltage doubler


This very stern looking gentleman is about to explain how voltage doubles work in a plodding, yet satisfyingly thorough manner.

We’re not certain when this US Air Training Command video was produced. Obviously it was used to train servicemen who were responsible for keeping electronics running during war time. We’re glad for that, as they really found just the right balance to present a concept that required some knowledge, but is approachable for even the most basic of new electronics hackers.

The demonstration board shown on the right is the voltage circuit highlighted in the lesson. Here the pointing stick is being used to trace out the circuit function during one phase of the input transformer. The capacitor/diode pairs rectify the voltage, with the capacitors discharging in parallel series to double the output voltage. But how does the variable load (RL) affect the output? This is demonstrated under several different conditions using an oscilloscope to illustrate the change.

The discussion of how the diodes work reminded us of a modern tutorial we just ran across this weekend. It’s a bit bizarre, but explains the PN junction in a different way than we’re accustomed to. In this case you will already need to be familiar with how semiconductors work to understand the presentation.

Both clips can be found below the jump.

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Retrotechtacular: A tour of WLW, a 500,000 Watt radio transmitter


This is an overview of a 500,000 Watt radio transmitter site. It’s one of the slides shared in a guided video tour of the transmitter’s hardware. The radio station — whose call sign was WLW — called itself the Nation’s Station because of its ability to reach so much of the country.

It operated at the 500 kW level starting back in the 1930′s. The technology at the time meant that there were a lot of challenges involved with transmitting at this level of power. It took 750 kW input to achieve the 500 kW output. To reach that the station had a set of AC motors in the basement generating the 4500 Amps at 33 Volts DC needed to power the transmitter to heat each filament. Obviously there was a lot of heat generated at the same time. The system was water-cooled. An elaborate network of Pyrex pipes carried distilled water to and from the tubes to handle the heat dissipation.

The video tour lasts about thirty minutes. It’s just packed with interesting tidbits from the experts leading the tour so add it to your watch list for some geeky entertainment over the weekend.

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Retrotechtacular: Vintage computer museum playlist


Have you ever seen one of these SCELBI 8B computers? This is one of the first hobby computer kits which were sold starting in 1974.

This is just one of the many pieces of vintage computing hardware shown off in this playlist (the SCELBI is the fifth video). The collection is part of the Bugbook Historical Microcomputer Museum. [Dave Larsen], the curator of the collection, has been accumulating historic and often rare hardware for decades. More recently he’s been making video documentaries of the pieces and posting them for your enjoyment.

We love museums, but this is something different. [Dave's] videos walk us through each exhibit, often filling in the story with anecdotes and insight from his own personal experience. It’s like a school field trip to the museum for those of us who can’t get enough of the moldy oldies.

We remember seeing at least one cool hack that used the 8008 processor also found in the computer pictured above. It was a clock built from a similar system.

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Retrotechtacular: History of the U.S. Antiballistic Missile Systems


On this installment of Retrotechtacular we’re taking a look at the history of the United States Antiballistic Missile System. The cold war was a huge driver of technological development, and this missile defense is a good example. At its most basic this is a radar system capable of tracking objects in three dimensions. It utilizes separate transmitters and receivers which are synchronized to rotate at the same time.

The movie, which is about forty-five minutes, came to our attention because of [Dammitd's] interest in the Luneburg Lens used by the system. At about 11:10 into the video after the break this component is discussed. Inside a dome like the one seen above is a reflector made of blocks of polystyrene foam which has been laced with bits of metal. This lens is stationary, with the receiver rotating around it to collect the transmitter’s waves as the echos bouncing off an object in the sky are focused by the lens.

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Retrotechtacular: The Fourier Series


Here’s a really quick video which takes a different approach to understanding the Fourier Series than we’re used to. If you’re a regular reader we’re sure you’ve heard of the Fourier Series (often discussed as FFT or Fast Fourier Transform), but there’s a good chance you know little about it. The series allows you to break down complex signals (think audio waves) into combinations of simple sine or cosine equations which can be handled by a microcontroller.

We’ve had that base level of understanding for a long time. But when you start to dig deeper we find that it becomes a math exercise that isn’t all that intuitive. The video clip embedded after the break changes that. It starts off by showing a rotating vector. Mapping the tip of that vector horizontally will draw the waveform. The Fourier Series is then leveraged, adding spinning vectors for the harmonics to the tip of the last vector. The result of summing these harmonics produces the sine-based square wave approximation seen above.

That’s a mouthful, and we’re sure you’ll agree that the video demo is much easier to understand. But the three minute clip just scratches the surface. If you’re determined to master the Fourier Series give this mammoth Stanford lecture series on the topic a try.

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Retrotechtacular: flying foot-soldiers are coming for you (sixty years ago)


Pictured above is a remarkable piece of experimental technology from the 1950′s that never ended up going anywhere. The Hiller VZ-1 Pawnee is a single-rider vehicle that was supposed to provide a tactical advantage to US forces. The Office of Naval research spent a couple of years developing the aircraft, wich uses two rotors mounted inside the base of the platform. They spin opposite each other — which removes the need for a tail rotor like you’d find on a helicopter –to lift the platform a short distance off the ground. Although six of them were made only two survive. But the good news is you can go and see them at museums on the East or West coast of the US.

Now that the serious business is behind us, let’s talk about the video clip after the break. The narrative style is a gem of the newsreel era. We can’t tell what is going on with the accent, but we’re totally convinced that at least one general meeting per year at your local hackerspace should require all presenters to use their best impression of this talented gentleman’s voice.

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Retrotechtacular: Mechanical targeting computers


The device that these seamen are standing around is a US Navy targeting computer. It doesn’t use electricity, but relies on mechanical computing to adjust trajectories of the ship’s guns. Setting up to twenty-five different attributes by turning cranks and other input mechanisms lets the computer automatically calculate the gun settings necessary to hit a target. These parameters include speed and heading of both the ship and it’s target, wind speed and bearing, and the location of the target in relation to this ship. It boggles the mind to think of the complexity that went into this computer.

The first of this seven part series can be seen after the break. The collection covers shafts,  gears, cams, and differentials. Sounds like it would be quite boring to sit through, huh? But as we’ve come to expect from this style and vintage of training film it packs a remarkable number of simple demonstrations into the footage.

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