Self Built Power Meter Uses Dual Sense Transformers

August 8, 2015 by Nava Whiteford 9 Comments

[Renaud] built a AC power meter from scratch. While commercial power meters like the Kill A Watt are available [Renaud’s] build gives an interesting insight into the methods used.

At the heart of [Renaud’s] design lie two sense transformers. The first is a typical voltage stepdown transformer. This brings the AC line voltage down to +/- 10V, which is more amenable to digital sampling. The second is a current sense transformer. In current transformers the primary is typically a single wire (the AC line in this case) passing through the middle of a ring (see the picture to the right from wikipedia). The secondary is wrapped round the ring. When the secondary coil is shorted a current in the primary wire/coil induces a current in the secondary coil.

In practice, the voltage drop across a low value resistor is used to detect the current in the secondary. Clamp meters use this principle to make non-contact current measurements. Other power meters often use hall effect sensors for current measurements. It will be interesting to see how these methods compare when [Renaud] benchmarks this build.

[Renaud] takes the voltage and current readings from these transformers and samples them with a PIC in order to calculate power. As the AC voltage is periodic [Renaud] uses a method similar to Equivalent Time Sampling (ETS) to combine waveforms from multiple cycles and increase the effective sample rate.

Great stuff [Renaud]!

Building A Dead-On-Accurate Model Ford Pickup From Scratch

August 8, 2015 by Adam Fabio 11 Comments

In a world filled with 3D printed this and CNC machined that, it’s always nice to see someone who still does things the old-fashioned way. [Headquake137] built a radio controlled truck body (YouTube link) from wood and polystyrene using just a saw, a Dremel, a hobby knife, and a lot of patience. This is one of those builds that blurs the lines between scale model and sculpture. There aren’t too many pickup trucks one might call “iconic” but if we were to compile a list, the 6th generation Ford F-series would be on it. [Headquake137’s] model is based on a 1977 F100.

The build starts with the slab sides of the truck. The basic outline is cut into a piece of lumber which is then split with a handsaw to create a left and a right side. From there, [Headquake137’s] uses a Dremel to carve away anything that doesn’t look like a 1977 F100. He adds pieces of wood for the roof, hood, tailgate, and the rest of the major body panels. Small details like the grille and instrument panel are created with white polystyrene sheet, an easy to cut material often used by train and car modelers.

When the paint starts going on, the model really comes to life. [Headquake137] weathers the model to look like it’s seen a long life on the farm. The final part of the video covers the test drive of the truck, now mounted to a custom chassis. The chassis is designed for trails and rock crawling, so it’s no speed demon, but it sure does look the part riding trails out in the woods!

[Headquake137] managed to condense what must have been a 60 or 70 hour build down to a 14 minute video found below.

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Hack Your Cat’s Brain To Hunt For Food

August 8, 2015 by Rick Osgood 55 Comments

This cat feeder project by [Ben Millam] is fascinating. It all started when he read about a possible explanation for why house cats seem to needlessly explore the same areas around the home. One possibility is that the cat is practicing its mobile hunting skills. The cat is sniffing around, hoping to startle its prey and catch something for dinner. Unfortunately, house cats don’t often get to fulfill this primal desire. [Ben] thought about this problem and came up with a very interesting solution. One that involves hacking an electronic cat feeder, and also hacking his cat’s brain.

First thing’s first. Click past the break to take a look at the demo video and watch [Ben’s] cat hunt for prey. Then watch in amazement as the cat carries its bounty back to the cat feeder to exchange it for some real food.

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DEF CON: Abusing Scripts In Multiplayer Games

August 8, 2015 by Brian Benchoff 11 Comments

Everyone has at least a few games on their computer, and I would assume most of the Hackaday readership would be among the enlightened PC gamer bretheren. At this year’s DEF CON, [Tamas Szakaly] gave a talk about the data these games leak to the Internet, the data they accept from the Internet, and what you can do with that data.

[Tamas]’ talk was entirely about scripting games, like the many games that are scriptable in Lua, or Valve’s Squirrel. Developers have thought about this before and have implemented sandboxes and many anti-cheat mechanisms. However, because these sandboxes are poorly implemented, it’s easy to get outside the game and do some real damage.

[Tamas]’ first target was Crysis 2 and the CryEngine3. This game uses a Lua scripting engine and has no sandbox whatsoever. That means [Tamas] can call os.execute, and from there the entire game is over. Or it’s just begun. Either way you look at it, it’s pretty bad.

CryTek notwithstanding, [Tamas] can also use games with Lua scripting that have a real sandbox. DOTA2 has a leaky sandbox and can be used to call OS I/O routines and execute base 64 encoded executables right over the main executable.

The most impressive example of script abuse in various multiplayer games is from Garry’s Mod. This game has custom implementation of dangerous functions, restricted file IO, and a proper Lua sandbox. This was a wise decision from the developers, but the library is huge. If you create a map or mode used on a server, you can have a full HTTP proxy to the gamer’s home network. During the talk, [Tamas] used this exploit to display an image from a webcam on a Garry’s Mod server. It was on the podium right next him, but this could have been done on a server on the other side of the planet.

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Hackaday Prize Entry: DIY Guitar Multieffects

August 8, 2015 by Brian Benchoff 14 Comments

Guitar effects and other musical circuits are a great introduction to electronics. There’s a reason for this: with audio circuits you’re dealing with analog signals and not just the ones and zeros of blinking a LED. Add in the DSP aspects of audio effects, and you have several classes of an EE degree wrapped up in one project.

For his Hackaday Prize entry, [randy.day] is building a guitar multieffect. Instead of just a single distortion, fuzz, or chorus circuit, this tiny little PCB is going to have several flavors of pitch shifting, a flanger, chorus, echo, harmony, and stranger ‘digital-ish’ effects like bitcrushing.

This effects unit is built around a PIC32 and a TI audio codec which processes the audio at 64k 32-bit samples/second. This takes care of all the audio processing, but the hard work for a guitar pedal is actually the enclosure and mechanicals – it’s a hard life for stage equipment. For the foot pedal input, [randy] is using a magnetic position sensor, but there’s no word if he’ll be using a fancy die-cast enclosure or a plastic injection molded unit.

The 2015 Hackaday Prize is sponsored by:

Cory Doctorow Rails Against The Effect Of DRM And The DMCA

August 8, 2015 by Mike Szczys 30 Comments

If you weren’t at [Cory Doctorow’s] DEF CON talk on Friday you missed out. Fighting Back in the War on General Purpose Computing was inspiring, informed, and incomparable. At the very lowest level his point was that it isn’t the devices gathering data about us that is the big problem, it’s the legislation that makes it illegal for us to make them secure. The good news is that all of the DEF CON talks are recorded and published freely. While you wait for that to happen, read on for a recap and to learn how you can help the EFF fix this mess.

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DEF CON: The Proxy For ProxyHam

August 7, 2015 by Brian Benchoff 23 Comments

Two weeks ago, news broke of an incredible abuse of power from the National Security Agency. A DEF CON talk was cancelled, and speculation raged that information was not free. This was the ProxyHam, a device that puts you miles away from any agency hunting down your IP address.

Of course, as with just about every DEF CON talk picked up by the press, ProxyHam is an ill-conceived, terrible idea. You can replicate it with parts bought from newegg, and despite using a highly directional antenna the FCC – or any other government agency – can still track you down.

In lieu of a talk on using off-the-shelf networking hardware in the way it was intended, [Dave Maynor] and [Robert Graham] of Errata Security gave a talk at DEF CON that is the proxy to the ProxyHam. They completely debunked the outrageous speculation surrounding the cancellation of the DEF CON talk and managed to introduce a new version of Internet over radio that is actually useful for the security-minded individual.

The ‘debunking’ part of the Errata Security talk was exactly what anyone would expect; the talk was probably cancelled because the creator of ProxyHam exceeded radiated power limits, the FCC caught him, or simply because of ‘advice from counsel’. No big deal; someone was doing something illegal – encryption over ISM bands – and the things you would expect to happen in fact happened.

In the last two weeks, the guys replicated the ProxyHam build, but found a few major shortcomings. Even with a highly directional antenna, interested parties could still track you down. This led the guys at Errata Security to make this system better. They managed to do it in two weeks.

The Errata Security relies on JT65A – a radio mode made for very weak signals – to hide signals underneath the noise floor. By multiplexing data across multiple channels, this system has about the same bandwidth as a 56kbps modem from 1999. It’s not much, but it is possible to use this proxy for ProxyHam over 20 miles away from where you’re stealing WiFi from. That’s far better than ProxyHam could ever manage, and all the transmissions stay below the noise floor. The FCC and similarly equipped agencies might be able to find you, but no one with a $20 SDR dongle will.

There are no releases yet, but Errata Security plan to make the software that allows this multiplex transmissions available soon, and hope to have a Raspberry Pi-based hardware solution for this technique coming shortly. It’s a radio proxy solution that’s actually somewhat secure, and won’t immediately draw the ire of the FCC.