Retrotechtacular: Transmission Lines

This great old video (embedded below the break) from Tektronix in the mid-60s covers a topic that seems to confuse folks more than it should — transmission lines. We found it on Paul Carbone’s blog, a great site for aficionados of old analog scopes in its own right.

As with many of these older videos, the pacing is a bit slow by today’s standards, but the quality of the material eventually presented more than makes it worth the effort to reign in your ADHD. For a preview, you can skip to the end where they do a review of all the material.

They start off 5:31 with a pulse travelling down a wire pair, and take a very real-world approach to figuring out the characteristic impedance of the line: if the pulse was created by a battery of 9V, how much current is flowing? If the DC resistance of the wire is zero then there should be an infinite current by Ohm’s law, and that’s clearly not happening. This motivates the standard analysis where you break the wire down into distributed inductance and capacitance.

Of course they do the experiment where you inject a pulse into a long loop of coaxial cable and play around with the termination at the other end of the line. They also measure the velocity factor of the line. Our only gripe is that they don’t tap the line in different places to demonstrate standing waves. The good news is that we’ve got YouTube (and [w3aew]) for that.

If you’ve got 23 minutes to spare, and are curious about transmission lines or just enjoy the soothing voice of a trained radio announcer reading out values of various termination resistors, this old gem is just the ticket. Enjoy!

Scrolling a Message on a Building in a Time Lapse Video

[Saulius Lukse] has a really interesting way of turning a couple of buildings into his own addressable display. The effect is not seen in real life, but is a clever video rendering with stock he pulled from time-lapse cameras. Now if you want to play Tetris using the windows of a building you add wireless lightbulbs to every window. But that’s a lot of work. You can fake playing Tetris (or scrolling messages in this case) if you just show a video of the buildings and swap in your own image manipulation.

[Saulius] starts with a time lapse sequence of a city scape. It needs to be one with a large building or two to provide a good scrolling surface. The building is extracted from the scene with the background transparent. The really time consuming part is creating a distinct image with one window lit for each window that is going to be used. This set of windows are the ‘pixels’ used to create the scrolling images. This is accomplished by masking out one image of the building with every office light turned off, then masking out each window individually with the office illuminated. This masking means everything going on around the building (traffic, weather, people) will be preserved, while the windows can be individually manipulated.

Next the program jinx is used to create the building animation. This program is designed to create scrolling messages on LED panels. [Saulius] provides a Python script that takes the images, the output of jinx, and combines them to create the final set of moving images.

The result is a city wishing you a “Happy New Year!”

Overunity, Free Energy and Perpetual Motion: The Strange Side of YouTube

Spend enough time on YouTube, and you’ll eventually find yourself in one of the many dark corners hiding within it. No, I’m not talking about the comments. In this case, I mean the many videos dedicated to free energy, overunity devices, perpetual motion machines, or anything else that violates the laws of thermodynamics by trying to get out more energy than is put in. The human race has been reaching for impossible dreams of perpetual motion and free energy for just about all of recorded history. Now it’s convenient to find them all in one place.

Browsing the tubes, it’s easy to break free energy videos down into two major groups: enthusiasts and scammers. Catching a scammer is easy – they’re looking for money. Somewhere in the video or description will be a link to a website with more information. Eventually that will lead you to a place where the scammer attempts to part you and your hard-earned money.

Names like John Searl, Muammer Yildiz, and M. T. Keshe go here. Searl especially deserves note because he’s been at it for decades.  Supposedly, his “Searl Effect Generator” SEG has been built several times, but the prototypes generate so much power they create their own anti-gravity field and fly off into space. Obviously this man and his staff need your money to continue their work. Scammers deserve disdain and public shaming. These are the folks who know their “discoveries” are nothing more than snake oil.

On the other side of the coin lie the enthusiasts. These are the backyard tinkerers, the ones who put down their computers, pick up their tools, and try to build something. Sounds a lot like the average Hackaday reader, doesn’t it? I have to admit I went into this article with the same disdain for the enthusiasts that I have for the scammers, possibly even more. In some cases, these are the folks who truly believe they can have a chance to violate the laws of thermodynamics. Inevitably these folks fail to build free energy generators, overunity devices, or whatever their pursuit is, but they all do seem to learn something in the process. A lot can be said about the builds themselves. Some of these are awesome devices. Even if they don’t work for their intended purpose, they are great demonstrations of magnetism or chemistry. This is where I had a change of heart. If someone wants to spend their time working on an impossible hack, then more power to them. I may not think they have any chance of success, but at the very least, they’ll learn how to build.

Increasing cable length in precision video applications

Transmitting video signals over long distances can be tricky. Cheap co-ax cables won’t do the job. You either need amplifiers along the path, or need to use expensive, high quality shielded co-ax cables – both of which can end up costing a lot. [Maurizio] built a low cost solution to transmit video over long distances using twisted pair cables.

The system is cheap and uses readily available parts. The idea is to convert the video signal into a differential output using a pair of op amps and transmit them over a pair of twisted pair wires, then extract the signal at the receiving end using another amplifier.

A differential amplifier usually requires a dual-polarity power supply, which may not be available when adding this upgrade to an existing system. To over come this limitation, [Maurizio] uses a bias voltage equal to half of the power supply value. This bias voltage is added to the non-inverting amplifier signal, and subtracted from the inverting amplifier signal. The resultant differential signal is then fed into the twisted pair cable through impedance matching resistors. At the receiving end, a single amplifier receives the differential signals and outputs a signal that corresponds to the original video signal.

This symmetrical configuration renders the system immune to external noise. The design was tested for transmitting video on inexpensive CAT-3 twisted pair wire. According to him, when transmitting on 300m of wire, good quality color video was displayed on a monitor with an NTSC input. He used LMH6643 op-amps for this experiment, but other devices with similar characteristics can be used. Here’s a useful PDF document that discusses signals, cables and connections.

If you want to check out more of [Maurizio]’s work, see how he figured out how to send serial data from Excel.

Video Standards Are More Than Video Signals

The number of hours we spend staring at screens is probably best unknown, but how about the technology that makes up the video on the screen? We’ve all seen a reel-to-reel projector on TV or in a movie or maybe you’re old enough to have owned one, surely some of you still have one tucked away real nice. Whether you had the pleasure of operating a projector or just watched it happen in the movies the concept is pretty straight forward. A long piece of film which contains many individual frames pass in front of a high intensity lamp while the shutter hides the film movement from our eyes and our brain draws in the imaginary motion from frame to frame. Staring at a Blu-ray player won’t offer the same intuition, while we won’t get into what must the painful detail of decoding video from a Blu-ray Disc we will look into a few video standards, and how we hack them.

Why Starting a Kickstarter Could Kick Your Butt

So you’ve come up with a great idea and now you’re thinking about starting a crowdfunding campaign – and why not, all the cool kids are doing it. Now, let’s say you already have a working prototype, or maybe you even built a small run for friends online. You’ve made 10 here, or 20 there. Sure it took some time, but making 1000, or 10,000 would be so much easier once you get all the orders in, right? Wrong.

Before you even think of setting up something like a Kickstarter, we would like to invite you to have a seat and watch this series of videos covering the things many people don’t know about manufacturing. It’s going to cost you 7 hours of sofa time, but if you’re serious about getting something to production these seven hours will pay in spades. Dragon Innovation has had many notable clients over the years – Pebble, Sphero, Makerbot, to name a few. They help startups find their way through the manufacturing mine-feild, for a fee of course. The founders are former iRobot employees, and have quite a bit of hard fought, yet free knowledge to share.

You’ll learn about how important decisions early on can make huge impacts on the success or failure of a product. There’s quite a bit of raw technical info on injection molding, design for manufacture, testing, pricing and everything under the sun. So do yourself (and everyone else) a favor, and before you click submit on that Kickstarter campaign, sit back and enjoy this free seminar.

We’re really enjoying the manufacturing oriented videos which have been popping up. Just a couple of weeks ago we came across a pair of hardware talks from [Bunnie Huang] that were a pleasure to watch. At 20 minutes this might be a good primer before you take the plunge with the playlist below.

Random Parcel Launches Steganographic Compulsion

A mysterious CD arrives in the mail with a weird handwritten code on it. What should you do? Put it in the computer and play the thing, of course!

Some might be screaming at their screens right now… this is how modern horror films start and before you know it the undead are lurking behind you waiting to strike. Seasonal thrills aside, this is turning into an involved community effort to solve the puzzle. [Johny] published the video and posted a thread on reddit.

We ran a similar augmented reality game to launch the 2014 Hackaday Prize solved by a dedicated group of hackers. It’s really hard to design puzzles that won’t be immediately solved but can eventually be solved with technology and a few mental leaps. When we come across one of these extremely clever puzzles, we take note.

This has all the hallmarks of a good time. The audio spectrogram shows hidden data embedded in the file — a technique known as steganography. There are some real contortions to make meaning from this. When you’re looking for a solution any little hit of a pattern feels like you’ve found something. But searching for the decrypted string yields a YouTube video with the same name; we wonder if they’ve tried to recover steganographic data from that source?

[Johny] mentions that this parcel was unsolicited and that people have suggested it’s a threat or something non-sensical in its entirety. We’re hoping it’s a publicity stunt and we’re all disappointed in the end, because solving the thing is the best part and publicity wouldn’t work if there was no solution.

The bright minds of the Hackaday community should be the ones who actually solve this. So get to work and let us know what you figure out!