Hackaday Links: September 22, 2013


First we start with some protection… for your USB charged devices. Here’s a USB Condom which acts as a pass-through for the power rails but not the data lines. This prevents untrusted charger security exploits. [Thanks Markus]

[OutKastz] seems to think he’s uncovered a price matching conspiracy at Best Buy. His post references an HDTV video wall he has built. But he also discovered that there are two different version of the same television sold as the same SKU. His theory is that this prevents the big box from matching prices on half of their inventory.

When you’re in need of some breadboarding action with your Raspberry Pi and want to make it as painless as possible you need to build your own Pi Cobbler. This is the diy version of an Adafruit product, built using a couple of pin headers, stripboard, and an IDE cable.

Speaking of Adafruit, did you see Ladyada’s teardown of an ICEdot crash sensor?

[Phineas] is showing off a really really small hexacopter. Check out the maiden flight, as well as first indoor and first outdoor tests.

Perhaps this coded entry system will inspire a future project for you. It uses piezo elements to enter a code which unlocks the back door to the company. The glass door already had a series of large dots painted on it. This turns out to be a nice interface for a four button code system.

Many projects use a Raspberry Pi as a web server. But there is more than just one flavor available. [Jeremy Morgan] performed a variety of Pi server benchmarks using Nginx, Monkey, Lighttpd, and Apache. [Thanks Walter]

Can an old TV antenna reflector be used to boost the range of a WiFi dongle? We’re a bit skeptical. Let us know what you think in the comments.

And finally, we do wish there was more information on this upright piano used to play Doom [Thanks Itay].


42 thoughts on “Hackaday Links: September 22, 2013

  1. About the different tv’s under the same sku, i highly doubt they use that for “price fixing” . It’s for them the same functional item, seen it’s re branded stuff anyway (Vizeo has no production lines) most likely they simply have 2 production sources for the same delivery to Best Buy…

    1. In this case, you’re probably right.

      But more frequently it’s the reverse scenario – the exact same product is sold by different major retailers under different model numbers. I’ve known about that for years, and have seen many examples; including but not limited to at Best Buy. That does make it impossible to price match. Or even to comparison shop for the best price in a straightforward manner, as you won’t find that model number offered at any competitor.

      Sometimes there is an additional, single difference – the cheaper version may have a shorter warranty. Which certainly makes me wonder about expected long-term reliability, if the manufacturer can justify such a price reduction. Caveat emptor.

      1. Warranty cost a lot of money, It does not say necessarily say anything about the longevity of the item itself.
        A prime example is the EU “dollar tax” (= something costing 100 usd in the us costing 100€ – 35% more – in the EU )
        Apart from tax differences consumers have by default 2 year warranty on items in the EU ( http://europa.eu/youreurope/citizens/shopping/shopping-abroad/guarantees/ ) and this is often “forgotten”.
        To get an 2 year “extended” warranty in the US on an 100 usd item, you will be paying something like 20 to 30 usd “extra” and the “real cost” of this warranty will be most likely in the excess of 10 usd / Item for the seller.

      2. “Rebadging” products is as old as the hills. Usually the different warranties are a function of individual company’s policy, or of different means of forecasting coming up with different optimal points.

    2. My guess as to why two versions of product X bought with a timeframe between them can be functionally identical but have physical differences isn’t down to price matching but economics – the manufacturer / product designer may have figured out a way to make product X cheaper whilst keeping all of it’s functionality (and perhaps add new functions without encurring extra costs).

    3. I disagree, I used to work at an appliance store, and when big box retailers started coming out with price matching, it was often for the exact model number of the appliance, Therefore, another retailer’s model XFG12c, could not be used to get a discount on their (identical) model (same features, same manufacturer) because their model number was XFG12km.

  2. What concerns me with the piezo knock hack is the proximity of the RFID reader to the door and the fact that they’re just leaving an RFID card on a stick to swipe in front of the reader.

    Isn’t RFID normally supposed to be used for audit control on locks like those? I wouldn’t like to know I had a security breach, look at my control log, and just see that the “knock” card was swiped.

    It doesn’t help when someone could easily jack the card as well for the future.

    1. I made one by just soldering a USB plug & socket together.

      DX has sold cables – even with a switch so you can turn the data lines on & off – in various configurations like this for years, try item #127844 (first I found at random).

      I decided their little cable took up too much space, hence DIY (and I thought the data switch was a bit useless).

    2. I thought the same thing.

      in fact when I wanted to make the opposite (signal but now power) for my 3d printer, I just took a screw driver and some pliers and scratched up and pulled out the pins from the plug.

      I would sort of suggest that anyone wanting this should do the same, get a cheap cable and adaprt the cable, not make a special board. but then, your device will only trickle charge as there won’t be the correct resistors etc to request higher currents. (i see that they are going to update the board to add high current resistors. in the datalines)

      I did the same thing with the pi cobbler.
      But also broke out all the pins of P5 and the reset switch on Pin 6. still yet to actually do anything noteworthy with the Raspberry pi, but at least it’s all ready even if I’m not!

    3. Same here, US$1.5 later, I have a USB-A plug / socket with floating datalines on the power side, and shorted data lines on the phone side. Viola, any charger will now charge my phone, provided mains voltage isn’t wired to the usb socket.

  3. Aaah the USB condom. When did USB devices start communicating with their dumb chargers anyway? Back in the old days when I had a Nokia N900, it seemed to use the proper USB standard which is *attempt to communicate* oh there’s nothing there to respond, I guess I’ll just draw as much as I need unless the voltage drops badly. It did however fail at the other side which is *attempt to communicate* oh hello you’re a computer are you? You can supply 25A can you? Well, I’m meant to negotiate this but just to be on the safe side I’ll draw 100mA. That wasn’t even enough power to turn the screen on.

    Solution, tape over the data pins of a cable.

    1. Right about when phones got smart. And the USB Charging Spec got released. Some phone refuse to work on dumb vcc/gnd only chargers. Most use 2 resistor voltage dividers on the data pins to signal type of charger (500ma/pc connection) or high current (700ma to 1A) or super high (ipad 2.1A chargers). As well as using the usb port for audio or composite tv or remote/dock. The usb port is a swiss army knife now.

    2. Well, for public charging stations you don’t really know where that cable leads to. Because that cable might lead to a PC without you knowing it, and some monkey is already browsing your files, or whatever.

    3. Not too long ago, I spent a day in a hospital waiting room.
      There was a long (Bar like) counter top with
      charging cords “sprouting” from holes all along its length.
      No way to see where the cords went to…
      Was interesting to see so many of the people
      looking like a junky who had spotted a dealer
      when they first saw it.
      Throughout a long day the ones playing games, etc
      went back a 2nd or 3rd time for a charge.
      It made me wonder what the potential risks
      were in this setup.

    1. Yeah, the spacing is fine enough that it should offer a fair amount of reflection, even if it’s not ideal. At 0.5λ (approx. 6cm) spacing the “dish” would effectively be useless, at 0.25λ (3cm) 50% of the signal is reflected, effectively 3dB down on efficiency, but even so, perhaps better than nothing. That spacing is much finer still, so maybe only 1dB down on a solid reflector.

  4. Just two comments, the USB antenna booster looks like the Asian Strainer booster, just more expensive (unless you get the antenna at Goodwill.) And as for the USB Condom, how the **** do I put that on my ****!?

  5. I don’t want to be rude, but I find the usb condom to be a useful product
    If you really worry that much, you could buy a cheap no name cable for like $5 and take some of the outer plastic off and cut the two wires that aren’t red and black then tape it back over, with the added benefit you don’t have something to break thats sitting in between the cable

  6. Regarding the USB Condom, it looks like the creator missed an obvious opportunity. It appears to be just a board with two connectors, and no other parts. It’s oversized, with plenty of empty space. And he’s charging $10 for it. So WHY not add the few cents of parts needed for an overvoltage clamp, and protect against ill-regulated chargers as well? Those are FAR more commonly encountered than exploits. Even if he charges a buck or two more, I’m sure the type of people who would consider buying such a device would gladly pay the extra, rather than purchasing a leaky condom.

    1. ^ This!
      Didn’t even think about being able to “Safely” use dodgy charges when nothing else is available.

      Maybe add something to detect a voltage divider from the source so it can in turn enabled a voltage divider across it’s data pins

      1. You can get chips that go through the various resistance combinations until the ‘correct’ one is found (that’s when the current on the power lines goes up).

        There shouldn’t be too many valid combinations (Apple has a few etc) so a simple rotary switch would work swapping the resistors in & out.

        All a bit silly from an engineering point of view.

  7. That USB condom is a nice idea. For ten bucks though I’d like to see over-voltage protection and a switch to enable/disable data. Also, why put it on the micro-usb side? Surely it would be more useful as a full-size USB connector – you could use it with more devices and all you have to do is stick it at the other end of the cable…

  8. $10 for an awkward ugly oversized exposed circuitboard that simply stops the data lines from connecting to your phone? Seems like there’s a perfect opportunity for an enterprising Chinese company to make miniature versions no bigger than the size of a plug+socket, and sell them for just a few dollars (if that).

  9. couldnt you just take usb charging cable and cut the data pins and use that cable only to use on untrusted charging ports?

    cutting wires only work if the untrusted charger is just a usb port but some charging booths may have the other end hanging out and you cant get to their source .

    apple could fix this problem and force the patch by making the itunes store not allow purchases from older versions (new firmware and itunes required)

    price matching is done where the store eats the loss on the item and makes it up through the profits on the item sold to tv addict has less than 1 hour before the super bowl comes on to replace a tv fried by lightning that came from thunder snow and does not have time for price matching, discounts and such (the pay and go).

  10. update on the usb suggestion:

    i think they make disposable emergency chargers as well as ones that use aa and aaa batteries so if you are going to carry a board wouldnt it be better to use one of them disposable or reusable emergency chargers?

    then you would not ever have to connect to an untrusted charger

    1. As many have pointed out before, there are many places where there are no mains sockets but where there are USB charging sockets for the public.
      Mains is just a tricky thing to make available to people, both in practical as well as in a legal sense. (If people electrocute themselves or cause fires or blow up expensive devices by expecting the wrong mains voltage then who gets to pick up the bill and/or go to jail?)

  11. I used to work at Staples and can confirm the price maching conspiricy. All loss-leader electronics like TV’s and laptops have different UPCs than other stores. Walmart goes so far as to require that most low end HP laptops have a “WM” attached to the end of their serial number. The companies will only price match if the UPC is identical and they have it in stock. The real money comes from the warranties which, at Staples, was 100% profit for the company. That is why you are houned to buy one. The employees have a quota.

    1. This is exactly it. Companies will do this to in effect negate their “wonderful” pricematch programs on quite a few items. This is why I seldom rarely shop at brick and motor stores anymore for anything but food and other necessities. Otherwise I’m using Amazon, Ebay, and many other online retailers. I used to work for a certain home improvement store and they did the exact same thing on tools among many things. I believe they still do it. As a cashier life sucked, because you would constantly have middle and upper managers baggering you to get warranty add on sales. These warranties often did nothing for the customer when they bought them, as there were certain fine print rules and regulations, that an unknowledgeable customer could easily break and then void the warranty. Again this also made life interesting when irrate customers would come in complaining about this. The warranties and other programs (credit cards, rewards cards – you’re information is eventually sold no matter what a cashier may tell you or it says in the information) were pure profit for the store, so I imagine it’s like this anywhere else. I don’t use big chain stores anymore for this reason. If I can’t wait to get it through comparative shopping online and the shipping, then I really don’t need it.

    2. I’m not really getting the reasons for doing that (really , not trolling).
      If you come in and they wont undercut the other store’s price then you simply get it at the other store, no? (and don’t bother the next time and simply get it directly at where you think it’s the cheapest…)

      Here in the eu you have “Mediamarkt” doing a slightly better scam which i “understand”, they have a price match and because of that claim to be cheap (their not :) ).
      If you come in they will price match directly (just come in with a picture on the phone or so of an other locale retailer of the item with a price visible , done it myself because the other store was out of stock :) ) but never adapt the display/store price (they do promise you to do it in their adverts, but who’s going back the next day to check anyway?).
      Double win : the “annoying” customers who bother checking prices feel good (so might brag about it = free pub) and the other who don’t simply believe it’s a cheap price but don’t bother checking.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.