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Planet hack-day

  • Tuesday, March 18, 2014 - 09:01
    Handheld Tetris is Retro and We Love It

    handheld tetris

    [Eduardo Zola] has been playing around with Arduinos, and ever since he started, he wanted to try making a game. Having fond memories of playing Tetris back on Windows 3.1, he decided to try giving a handheld version of it a shot.

    He started with two 8×8 Neopixel Matrices due to their simplicity — not to mention the massive library of code available! To make it truly portable, he’s also included a 3.7v 4400mAh lithium ion battery which will keep him gaming for hours. He found a 5-way navigation switch on eBay which makes up the joystick. A small LED bar display tells you what level you’re on, and he’s even included a smaller speaker for music, and a vibrating motor for successfully completed lines in the game!

    He borrowed the Tetris algorithm (and added some improvements) from the source code by [Valentin Ivanov], who completed a similar project last fall. Stick around to see a demonstration video of it in action.

    We’re still pretty fond of this Tetris playing LED necktie though…

    Filed under: Arduino Hacks, led hacks

  • Tuesday, March 18, 2014 - 06:01
    Cute Tilt Beam Flashlight Adds Some Fun Interaction to Your Patio Table


    Here’s a cute little LED hack for your next soiree, it’s a solar charged piece of wood… with a motion controlled light in it!

    [Zach DeBord] decided to try building his own version of this after seeing a commercial offering. He took a piece of oak and sliced off the top edge, and then laser cut the exact profile of the solar panel out of that slice. This allowed him to drill a nice big sloppy hole in the middle of it to fit the circuitry.

    He’s using a nice big 8mm LED with a small 0.09V-5V DC boost circuit, a mercury tilt switch, a 4.5V solar cell, and a 2.7V 10MF super capacitor — plus a diode and 100ohm resistor. He’s glued the top slice of wood back in place, and sealed the entire thing with resin — you can hardly see the cut mark!

    Leave the light with the solar panel facing up during the day, and when evening comes around, simply flip it on its edge to light up your table. And since it’s a super-capacitor, the circuit will likely last longer than you do. We’re not too sure how long the light lasts after a charge though.

    Or if you really want to impress your guests, why not make a solar powered remote controlled lawn mower?

    Filed under: led hacks, solar hacks

  • Tuesday, March 18, 2014 - 03:00
    MRRF: Repables, The Nonprofit 3D Object Repository


    There’s a problem with online repositories of 3D printable objects: The largest repo, Thingiverse, is generally looked down upon by the 3D printing community. Thingiverse, owned by Makerbot, has seen protests, and calls for a an alternative repository. A few people have stepped up to provide a better Thingiverse, but these alternatives are either connected to specific 3D printer manufacturers like Ultimaker’s YouMagine, or have done some shady things with open source licenses; Defense Distributed’s DEFCAD, for example.

    Repables, launched at the Midwest RepRap Festival this last weekend, hopes to change that. They are the only repository of printable objects and design files out there that’s backed by its own nonprofit LLC. It’s free for anyone to upload their parts and share, without the baggage that comes with an ‘official [company name] .STL repo’.

    Just about everything can be hosted on Repables – .STL files for printable objects, .DXF files for laser cutter files, and even PCB files and Gerbers for circuit boards. Now, .STL files are able to be rendered in the browser, with support for viewing other formats coming soon.

    It’s a really great idea that solves the problem of printer manufactures building their own hosting sites and the segmentation that ensues. It’s also headed up by a Hackaday alumnus, []. We’re everywhere, it seems.

    Filed under: 3d Printer hacks, news

  • Tuesday, March 18, 2014 - 00:01
    Good Vibrations: Giving the HC-SR04 a Brain Transplant


    [Emil] got his hands on a dozen HC-SR04 ultrasonic sensors, but wasn’t too happy with their performance. Rather than give up, he reverse engineered the sensor and built an improved version. Hackers, Makers, and robotics enthusiasts have had easy access to standard sonar platforms since the early 1980′s, when Polaroid began selling their 6500 sonar modules. A number of companies have released sonar boards since then, notably The Parallax Ping))) module. The HC-SR04 appeared on the market a few years back as a low-cost alternative of the Ping.

    [Emil] found that the HC-SR04 would work reliably on hard surfaces as far as 4 meters away from the sensor. However, he got a lot of bad data back when using soft sided targets, or when no target was present at all.  [Emil] reverse engineered the schematic of the HC-SR04 and found some interesting design decisions. A Max232 RS-232 converter chip is used for its +-12V +-10V charge pumps. The charge pumps are connected to create 24V 20V at the ultrasonic transmitter. A mask programmed microcontroller manages the entire unit, commanding the ultrasonic transmitter to send 40Khz pulses, and listening for returns on the receive side of the system. [Emil] believes the micro is running in polled mode, due to the fact that it sometimes misses pulses. Even worse, the micro runs on an unmarked 27MHz crystal which had quite a bit of drift.

    [Emil] solved these problems by creating his own PCB with an ATtiny24 and a 12MHz crystal. He increased the pin count from 4 to 6, allowing the ATtiny to be programmed in circuit, as well as opening the door to I2C and SPI operation. To build the boards up, [Emil] first solders his micro and crystal. He then uses a hot air gun to move all the components from the HC-SR04 board to his own. The new boards are still being tested, but [Emil] has posted his PCB and BOM data. He’s also promised to post his AVR code when it is available.

    Filed under: misc hacks

  • Monday, March 17, 2014 - 21:00
    MRRF: Stuff From Lulzbot


    A lot of the big names in 3D printers were at the Midwest RepRap festival showing off their wares, and one of the biggest was Lulzbot with their fabulous Taz 3 printer. This year, they were showing off a new filament, a new extruder, and tipping us off to a very cool project they’re working on.

    The new products Lulzbot is carrying are Ninjaflex filament and the extruder to go with it. Ninjaflex is the stretchiest filament we’ve ever seen, with the feel of a slightly hard silicone rubber. Straight off the spool, the filament will stretch to a little less than twice its original length, and in solid, printed form its a hard yet squishy material that would be perfect for remote control tank treads, toys, and 3D printed resin molds. With all the abuse the sample parts received over the weekend, we’re going to call Ninjaflex effectively indestructible, so long as you don’t try to pull the layers apart.

    Also from Lulzbot is word on the new 3D scanner they’re working on. The hardware isn’t finalized yet, but the future device will use a webcam, laser, and turntable to scan an object and turn it directly into an .STL file. Yes, that means there won’t be any point clouds or messing about with Meshlab. Lulzperson [Aeva] is working on the software that subtracts an object from its background and turns it into voxels. The scanner will be low-cost and open source, meaning no matter what the volume of the scanner will be, someone will eventually build a person-sized 3D scanner with the same software.

    Videos of [Aeva] below showing off the new stuff and talking about the scanner.

    Filed under: 3d Printer hacks, news

  • Monday, March 17, 2014 - 19:01
    Hacking the Sci-Fi Contest Team Requirement


    We saw that some readers were not entirely happy with the team requirement for our Sci-Fi contest, which is running right now. We figured that those who do not work well with others might commit a bit of fraud to get around the requirement. But we’re delighted that someone found a much more creative solution. Why not enlist an AI to collaborate on your project?

    [Colabot] is a hacker profile over on hackaday.io which is driven by ELIZA, a computer program that achieves limited interaction through natural language. Supposedly you add [Colabot] to your project and as it questions. We asked one on the profile page and are still awaiting the response. We think this itself could be a qualifying entry for the Sci-Fi contest if someone can find the right thematic spin to put on it.

    As far as contest entries go there are only seven so far. Since everyone who submits an entry gets a T-shirt, and there are 15 total prize packages, we encourage you to post your entry as soon as possible. We want to see teams from hackerspaces and we can cryptically tell you that good things come to teams who post their project with the “sci-fi-contest” tag early!

    Filed under: contests

  • Monday, March 17, 2014 - 18:01
    Radar Imaging in your Garage: Synthetic Aperture Radar


    Learn why you were pulled over, quantify the stealthiness of your favorite model aircraft, or see what various household items look like at 10 GHz. In this post we will describe the basics of Synthetic Aperture Radar (SAR) imaging, beginning with a historical perspective, showing the state of the art, and describing what can be done in your garage laboratory. Lets image with microwaves!


    The H2S radom (antenna covering, above) and antenna (below).

    The History of SAR

    Ground mapping (or imaging the ground terrain) using microwave radar was done routinely in the Second World War by the Royal Air Force for the purpose of navigation and bomb laying using the H2S radar system. The H2S used a large aperture rotating antenna in the belly of a bomber aircraft. This antenna would rotate in circles with its beam directed toward the ground. Range to target was plotted in a plan position indicator (PPI, or a radar screen as most would recognize it) showing what was below and around the aircraft.

    The angular resolution of this radar set depends on the antenna aperture size (e.g. antenna size). The bigger the aperture the finer the angular resolution, just like the reflector on a flashlight provides a tighter light beam the larger it is (this is why spotlights shine tight beams well into the sky). A typical example of an H2S radar image is shown below recorded during s bombing raid over Berlin. In this image the river is clearly visible as well as other blob-like targets which are landmarks that a trained operator would recognize.


    Radar ground image of Cologne during a bombing raid in the Second World War.

    Earlier versions of the H2S were at S-band (3 GHz) and later higher resolution sets were at 10 and 24 GHz (for an interesting read on this technology, Echos of War: The Story of H2S Radar).

    Synthetic Aperture Radar (SAR) is a modern ground mapping technique where high resolution is achieved by a very large aperture that is synthesized over the flight path of an aircraft. This is done by recording reflected radar pulses at known locations along the flight path. The radar must accurately know the aircraft’s position and back-out perturbations in flight path so that all scattered pulses are aligned in time and phase. After this a SAR imaging algorithm is applied to the data to process an image.


    An aircraft (or other moving vehicle) synthesizes an extremely large aperture by recording scattered radar pulses over the flight path and processing these pulses in a SAR imaging algorithm, thereby synthesizing a very large aperture which provides high angular resolution.

    Developments in SAR Technology

    This technique was first developed in 1957 using photographic film to record the radar data and an image processor made from lenses. Today digitizers and other data acquisition equipment can store data for offline processing or even process imagery in real-time.

    State of art airborne SARs include the MIT Lincoln Laboratory LIMIT system (PDF), which operates at X-band (10 GHz) and is mounted on an old 707 aircraft for testing advanced SAR imaging concepts.

    Another is the Sandia National Laboratory’s Ka Band SAR imaging system (to see an amazing portfolio of airborne SAR imagery visit here PDF), an example airborne SAR image from this system is shown below.

    image from Sandia's system

    SAR imagery from the Sandia National Laboratory’s Ka band airborne SAR imaging system.

    SAR imagery appears to be nearly photographic but it is not a photograph, it is a 2D hologram. Unlike a satellite image the radar is not measuring the target scene from above it is measuring from the side at a fairly significant distance. The resulting image is a birds-eye view with many shadows where each pixel is mapped directly to the aircraft’s flight path in range and cross-range.

    Most recently, small and light weight airborne SAR imaging systems weighing only a few lbs have been developed for micro-UAVs, for example the NanoSAR imaging system manufactured by IMSAR.

    Create your own SAR imaging system.


    To SAR image in your garage, try making a rail SAR imaging system, where a UWB radar sensor moves down well controlled path on a linear rail.

    Airborne SAR imaging is beyond the means of most hackers and hobbyists. The good news is that you can do it yourself with better resolution if you limit the scope of the problem and reduce maximum range, power, and the complexity of your radar sensor. To achieve this consider the rail SAR imaging system. In this, an ultrawideband (UWB) radar device is mounted on a long linear stage (typically 6′ to 8′ in length). The radar pulses once, moves, pulses again, each echo is recorded. This process repeats itself along the rail until a complete data set is acquired.

    For the UWB radar sensor you can use one of the sensors described in my previous post that is either an impulse or an FMCW radar or create your own. For the linear rail stage you can use anything from a Genie garage door opener assembly (which contains a lead screw inside of a long aluminum extrusion with a car that rides on the threads) to one stage on a full-size CNC router table.

    Make your own from junk parts

    One example of a hacked-together rail SAR is the ‘backyard SAR’ imaging system, where an X-band UWB FMCW radar front end was mounted to an 8′ long linear stage built from a Genie garage door opener, a cordless drill transmission, and a stepper motor following the block diagram shown. X-band microwave components were acquired at hamfests.


    Block diagram of the ‘backyard SAR’ imaging system.


    The ‘backyard SAR’ imaging system, deployed in my backyard.

    To process data from a rail SAR like this follow the procedure outlined in the Range Migration Algorithm chapter from Spotlight Synthetic Aperture Radar: Signal Processing Algorithms, which follows these steps:

    1. Cross range discrete Fourier transform (DFT).
    2. Apply matched filter.
    3. Perform Stolt interpolation.
    4. 2D IDFT into image domain.

    When implemented correctly this will result in the imagery shown below, achieving approximately 1×1” resolution at X-band with approximately 5 GHz of chirp bandwidth.

    Learn why you were pulled over, radar image of my 5.0 Mustang, apparently the headlights reflect the most microwave radiation!
    Radar image of 'GO STATE' in thumbtacks.
    Radar image of my Cannondale M300 mountain bike.
    Radar image of a scale F14 model.

    Build the coffee can radar kit

    The MIT coffee can radar kit is capable of producing coarse SAR imagery.

    To make SAR imaging accessible the MIT ‘coffee can’ radar course was developed, where you can SAR image with the coffee can radar. The goal of the SAR imaging experiment was to show students it is possible to differentiate in both rang and cross range when imaging some very large targets.

    The coffee can radar does not produce the best imagery but it shows a concept to students. To acquire an image, it is placed on a linear track with a tape measurer for a position reference. This could be a length of 2×6” or a straight rail somewhere. The radar is manually moved in 2” increments where a toggle switch on the side mutes the synchronization signal output, showing the computer that the radar has moved.

    Resulting in imagery comparable to that shown below.

    SAR imaging with the MIT coffee can radar
    SAR image of the Alexander Calder statue, La Grande Volie, 1968 (<a href="http://www.ll.mit.edu/news/iapradarcourse.html")
    SAR imagery of outdoor terrain using the MIT coffee can radar

    Give it a try, but be sure to image a large target scene. The algorithm is already written and the procedure is straight forward (scroll down to ‘Experiment 3: SAR imaging’).

    Many more examples of rail garage-made SAR imaging systems are shown here.

    Learning Curve

    It is not trivial to design, build, and write a an imaging algorithm for your backyard rail SAR. Caveats to implementation and processing include having to scale to your wavelength range, the need for calibration to a point target (a large pole or similar), use of coherent background subtraction, and other processing techniques. But we can philosophize about these all day, the best way to learn is to try it yourself:

    1. Learn by doing, build the MIT Coffee Can Radar and try the SAR imaging experiment.
    2. For a quick-read technical background read Chapter 4 and for details on numerous practical examples Chapter 5 in the book Small and Short-Range Radar Systems (use promo code EEE24 for discount).
    3. Process a SAR image right now. Download data sets for X and S-band and their associated processing algorithms written in MATLAB. With this you will learn how to apply calibration and coherent background subtraction.
    4. Need help? Post your questions to the Tin Can Radar Forum.

    With these resources, patience, perseverance, and coffee anyone can create a SAR imaging system in their garage.

    DSC_0318Gregory L. Charvat, is author of Small and Short-Range Radar systems, co-founder of Butterfly Network Inc., visiting research scientist at the Camera Culture Group MIT Media Lab, and editor of the Gregory L. Charvat Series on Practical Approaches to Electrical Engineering. He was a technical staff member at MIT Lincoln Laboratory from September 2007 to November 2011, where his work on through-wall radar won best paper at the 2010 MSS Tri-Services Radar Symposium and is an MIT Office of the Provost 2011 research highlight. He has taught short radar courses at the Massachusetts Institute of Technology, where his Build a Small Radar Sensor course was the top-ranked MIT professional education course in 2011 and has become widely adopted by other universities, laboratories, and private organizations. He has developed numerous rail SAR imaging sensors, phased array radar systems, and impulse radar systems; holds several patents; and has developed many other radar sensors and radio and audio equipment. He earned a Ph.D in electrical engineering in 2007, MSEE in 2003, and BSEE in 2002 from Michigan State University, and is a senior member of the IEEE, where he served on the steering committee for the 2010 and 2013 IEEE International Symposium on Phased Array Systems and Technology and chaired the IEEE Antennas and Propagation Society Boston Chapter from 2010-2011.

    Filed under: Featured, how-to, radio hacks

  • Monday, March 17, 2014 - 15:01
    NFC Ring Unlocks Your Phone

    NFC Ring

    This little ring packs the guts of an NFC keyfob, allowing [Joe] to unlock his phone with a touch of his finger.

    The NFC Ring was inspired by a Kickstarter project for a similar device. [Joe] backed that project, but then decided to build his own version. He took apart an NFC keyfob and desoldered the coil used for communication and power. Next, he wrapped a new coil around a tube that was matched to his ring size. With this assembly completed, epoxy was used to cast the ring shape.

    After cutting the ring to size, and quite a bit of polishing, [Joe] ended up with a geeky piece of jewelry that’s actually functional. To take care of NFC unlocking, he installed NFC LockScreenOff. It uses Xposed, so a rooted Android device is required.

    We’ll have to wait to see how [Joe]‘s homemade solution compares to his Kickstarter ring. Until then, you can watch a quick video of unlocking a phone with the ring after the break.

    Filed under: Android Hacks, wearable hacks

  • Monday, March 17, 2014 - 12:01
    MRRF: ARM-Based CNC Controllers


    8-bit microcontrollers are the standard for RepRap electronics, but eventually something better must come along. There has been a great deal of progress with ARM-based solutions, and of course a few of these made a showing at the Midwest RepRap Festival.

    First up is [Mark Cooper], creator of Smoothieboard, the ultimate RepRap and CNC controller. It’s an ARM Cortex-M3 microcontroller with Ethernet, SD card, and up to five stepper drivers. It had a Kickstarter late last year and has just finished shipping all the rewards to the backers. In our video interview, [Mark] goes over the functions of Smoothieboard and tells us about some upcoming projects: the upcoming Smoothiepanel will feature a graphic LCD, SD card, rotary encoder and buttons, all controlled over USB by the Smoothieboard.

    Next up is [Charles] with a whole bunch of CNC capes for the Beaglebone. By far the most impressive board was a huge I/O expander, motor driver, and everything controller for a Beaglebone featuring – get this – three parallel port interfaces. This was a one-off board costing thousands of dollars, but [Charles] did show off a few smaller and more practical boards for Beaglebone CNC control. Here’s a link to [Charles]‘ capes.

    Videos below.

    Filed under: 3d Printer hacks