Retrotechtacular: Transmission Lines

February 21, 2016 by Elliot Williams 13 Comments

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!

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Cute, Hackable, 3D Printable Robot Family

February 20, 2016 by Elliot Williams 9 Comments

We first saw the robot Zowi (top row in the banner photo) at Make Munich a few weeks ago, and we were very impressed by how much interesting motion they were getting out of the ‘bot for only using four servo motors. The combination of big feet, strong ankle joints, and clever programming let the cute little bot stand on one leg, do a moonwalk, and even hop. (See the video, below the break.) We knew it was for sale. What we didn’t know is that it was entirely open source.

[Javier Isabel], the inventor, is very good at giving credit where it’s due, and that’s a great thing because his ‘bot is basically an improved BOB robot. That said, you really need to see this thing moving to know what a difference Zowi’s significantly stronger servos and clever programming can make.

But that’s not all! Since everything about Zowi is open, and up on GitHub you can not only 3D print one of your own, but you can easily modify the attractively-boxy case. And a handful of people have taken [Javier] up on the offer, and submitted their modifications back as pull requests. So if you’d rather something mildly more humanoid, and are willing to add a couple more servos, there’s a good basis for your explorations ready to go.

We really like the idea of collaborative toy-robot design, and from what we’ve seen the basic Zowi platform is a winner. Check it out and see if you’re not inspired to add your own personal touch to the design. If you do, be sure to contribute back for others to see!

Thanks [Nils Hitze] for the tip!

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Good Vibrations In 3D-Printed Clay

February 20, 2016 by Elliot Williams 16 Comments

An engineer with a 3D printer wants everything to be rigid and precise. Wobble induced by flex in the z-axis feedscrews, for instance, makes telltale wavy patterns in the surface that match exactly the screw pitch. Nobody likes those, right? Certainly not an engineer!

But one man’s surface irregularity is another man’s ornamentation. The details we have are sparse, but from looking at the video (also inlined below the break) it’s clear enough: [Olivier van Herpt] and [Ricky van Broekhoven] stuck a vibrating woofer underneath the print bed of their ceramic printer, and use it to intentionally ruin their smooth surface. And they do so to great artistic effect!

We’re not suggesting that you give up entirely on your calibrations, but we do appreciate a little out-of-the-box thinking from time to time. But then our internal engineer raises his head and we wonder if they’re linking the pitch of the woofer to the feed rate of the print head. Your thoughts in the comments?

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Aquire Awesome Audio For BeagleBone

February 19, 2016 by Elliot Williams 13 Comments

[Henrik Langer] put his powerful audio acquisition and output board up on Hackaday.io, and we thought we’d point it out to you. It’s one of those projects that used to be pro audio just a few years back, but is doable (and affordable) DIY today: dual stereo inputs and four(!) stereo outputs, all sampled at 24 bits and up to 192 kHz. It’s configured as a BeagleBone cape, and comes with a customized Linux distribution for the ‘Bone.

What would you do with such a thing? It’s essentially a recording studio in your pocket, with a computer attached. The video (linked below the break) demonstrates using the device as a real-time stereo delay effect unit, but that’s only making use of one channel. Between effects, recording, and then all sorts of much-better-than-CD quality sound synthesis and playback possibilities, it’s an open-ended audio playground.

And all that from what is essentially a (very well-done) breakout board for a fancy DAC/ADC chip from Analog Devices: the AD1938. We’d love to have one of these on our desktop. Check out [Henrik]’s GitHub for the PCB and build instructions and BOM and everything else you’d need to get started. Very nice job!

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Barcodes That Hack Devices

February 17, 2016 by Elliot Williams 76 Comments

[virustracker] has been playing around with barcodes lately, and trying to use them as a vector to gain control of the system that’s reading them. It’s a promising attack — nobody expects a takeover via barcodes. The idea isn’t new, and in fact we’ve seen people trying to drop SQL attacks in barcodes long ago, but [virustracker] put a few different pieces together and came up with a viable attack.

The trick is that many POS terminals and barcode readers support command characters in their programming modes. Through use of these Advanced Data Formatting (ADF) modes, [virustracker] sends Windows-Key-r, and then cmd.exe, ftps a file down, and runs it. Whatever computer is on the other side of the barcode scanner has just been owned. ADF even supports a delay function to allow time for the command window to pop up before running the rest of the input.

The article details how they got their payload from requiring more than ten individual barcodes down to four. Still, it’s a suspicious-looking attack to try to pull off where other people (think cashiers) are looking. However, we have many automated machines in our everyday life that use barcodes. How many of these are vulnerable is an open question. [virustracker] suggests lottery machines, package-delivery automats, and even hospitals.

The defense is simple, and it’s the same as everywhere else: disable the debug and configuration modes in your production systems, and sanitize your input. Yes, even the barcodes.

Embed With Elliot: Audio Playback With Direct Digital Synthesis

February 12, 2016 by Elliot Williams 39 Comments

Direct-digital synthesis (DDS) is a sample-playback technique that is useful for adding a little bit of audio to your projects without additional hardware. Want your robot to say ouch when it bumps into a wall? Or to play a flute solo? Of course, you could just buy a cheap WAV playback shield or module and write all of the samples to an SD card. Then you wouldn’t have to know anything about how microcontrollers can produce pitched audio, and could just skip the rest of this column and get on with your life.

Harmonic distortion down ~45db on an Arduino — ~45db signal to noise ratio from an Arduino

But that’s not the way we roll. We’re going to embed the audio data in the code, and play it back with absolutely minimal additional hardware. And we’ll also gain control of the process. If you want to play your samples faster or slower, or add a tremolo effect, you’re going to want to take things into your own hands. We’re going to show you how to take a single sample of data and play it back at any pitch you’d like. DDS, oversimplified, is a way to make these modifications in pitch possible even though you’re using a fixed-frequency clock.

The same techniques used here can turn your microcontroller into a cheap and cheerful function generator that’s good for under a hundred kilohertz using PWM, and much faster with a better analog output. Hackaday’s own [Bil Herd] has a nice video post about the hardware side of digital signal generation that makes a great companion to this one if you’d like to go that route. But we’ll be focusing here on audio, because it’s easier, hands-on, and fun.

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Remote-Controlled Eyebrows For Your Birthday

February 10, 2016 by Elliot Williams 15 Comments

We’re not sure that [Alec]’s dad actually requested remote-controlled eyebrows for his birthday, but it looks like it’s what he got! As [Alec] points out, his father does have very expressive eyebrows, and who knows, he could be tired of raising and lowering them by himself. So maybe this is a good thing? But to us, it still looks a tiny bit Clockwork Orange. But we’re not here to pass judgement or discuss matters of free will. On to the project. (And the video, below the break.)

An ATmega328 (~~otherwise known as cheap Cloneduino~~ Alec wrote that the 328 was from a real Arduino) is trained to run motors in response to IR signals. An L293D and a couple of gear motors take care of the rest. Sewing bobbins and thread connect the motors to the eyebrows. And while it’s not entirely visible in the photo, and veers back into not-sure-we’d-do-this-at-home, a toothpick serves as an anchor for the thread and tape, secured just underneath the ‘brows for maximum traction.

We have to say, we initially thought it was going to be a high-voltage muscle-control hack, and we were relieved that it wasn’t.

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