A Cold Hard Look at FPGAs

Researchers at the Delft University of Technology wanted to use FPGAs at cryogenic temperatures down around 4 degrees Kelvin. They knew from previous research that many FPGAs that use submicron fabrication technology actually work pretty well at those temperatures. It is the other components that misbehave — in particular, capacitors and voltage regulators. They worked out an interesting strategy to get around this problem.

The common solution is to move the power supply away from the FPGA and out of the cold environment. The problem is, that means long wires and fluctuating current demands will cause a variable voltage drop at the end of the long wire. The traditional answer to that problem is to have the remote regulator sense the voltage close to the load. This works because the current going through the sense wires is a small fraction of the load current and should be relatively constant. The Delft team took a different approach because they found sensing power supplies reacted too slowly: they created an FPGA design that draws nearly the same current no matter what it is doing.

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DIY LiPo Protectors

Spiderman’s Uncle Ben was known to say, “With great power comes great responsibility.” The same holds true for battery power. [Andreas] wanted to use protected 18650 cells, but didn’t want to buy them off the shelf. He found a forty cent solution. Not only can you see it in the video, below, but he also explains and demonstrates what the circuit is doing and why.

Protection is important with LiPo technology. Sure, LiPo cells have changed the way we use portable electronics, but they can be dangerous. If you overcharge them or allow them to go completely dead and then charge them, they can catch fire. Because they have a low source resistance — something that is usually desirable — short-circuiting them can also create a fire hazard. We’ve covered the chemistry in depth, but to prevent all the badness you’ll want a charger circuit.

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Pulleys within Pulleys form a Unique Transmission for Robots

After a couple of millennia of fiddling with gears, you’d think there wouldn’t be much new ground to explore in the field of power transmission. And then you see something like an infinitely variable transmission built from nested pulleys, and you realize there’s always room for improvement.

The electric motors generally used in robotics can be extremely efficient, often topping 90% efficiency at high speed and low torque. Slap on a traditional fixed-ratio gearbox, or change the input speed, and efficiency is lost. An infinitely variable transmission, like [Alexander Kernbaum]’s cleverly named Inception Drive, allows the motor to stay at peak efficiency while smoothly changing the gear ratio through a wide range.

The mechanism takes a bit of thought to fully grok, but it basically uses a pair of split pulleys with variable spacing. The input shaft rotates the inner pulley eccentrically, which effectively “walks” a wide V-belt around a fixed outer pulley. This drives the inner pulley at a ratio depending on the spacing of the pulley halves; the transmission can shift smoothly from forward to reverse and even keep itself in neutral. The video below will help you get your head around it.

We’ve seen a couple of innovative transmissions around here lately; some, like this strain-wave gear and this planetary gearbox, are amenable to 3D printing. Looks like the Inception Drive could be printed too. Hackers, start your printers and see what this drive can do.

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Reverse Engineering Guitar Hero

What do you do when a ten-year-old video game has a bug in it? If you are [ExileLord] you fix it, even if you don’t have the source code. Want to know how? Luckily, he produced a video showing all the details of how he tracked the bug down and fixed it. You can see the video below. You may or may not care about Guitar Hero, but the exercise of reverse engineering and patching the game is a great example of the tools and logic required to reverse engineer any binary software, especially a Windows binary.

The tool of choice is IDA, an interactive debugger and disassembler. The crash thows an exception and since [ExileLord] has done some work on the game before, he was able to find a function that was creating a screen element that eventually led to the crash.

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Hackaday Prize Entry: OrthoSense, a Smart Knee Brace for Physical Therapy

If you have knee surgery, you can probably count on some physical therapy to go with it. But one thing you might not be able to count on is getting enough attention from your therapist. This was the case with [Vignesh]’s mother, who suffers from osteoarthritis (OA). Her physiotherapist kept a busy schedule and couldn’t see her very often, leaving her to wonder at her rehabilitation progress.

[Vignesh] already had a longstanding interest in bio-engineering and wearables. His mother’s experience led him down a rabbit hole of research about the particulars of OA rehabilitation. He found that less than 35% of patients adhere to the home regimen they were given. While there are a lot of factors at play, the lack of feedback and reinforcement are key components. [Vignesh] sought to develop a simple system for patients and therapists to share information.

The fruit of this labor is Orthosense, an intelligent knee brace system that measures gait angle, joint acoustics, and joint strain.  The user puts on the brace, pairs it with a device, and goes through their therapy routine. Sensors embedded in the brace upload their data to the cloud over Bluetooth.

Joint strain is measured by a narrow strip of conductive fabric running down the length of the knee. As the user does their exercises, the fabric stretches and relaxes, changing resistances all the while. The changes are measured against a Wheatstone bridge voltage divider. The knee’s gait angle is measured with an IMU and is calculated relative to the hip angle—this gives a reference point for the data collected by the strain sensor. An electret mic and a sensitive contact mic built for body sounds picks up all the pops and squeaks emitted by the knee. Analysis of this data provides insight into the condition of the cartilage and bones that make up the joint. As you might imagine, unhealthy cartilage is noisier than healthy cartilage.

[Vignesh]’s prototype is based the tinyTILE because of the onboard IMU, ADC, and Bluetooth. Since all things Curie are being discontinued, the next version will either use something nRF52832 or a BC127 module and a la carte sensors. [Vignesh] envisions a lot for this system, and we are nodding our heads to all of it.

Cuban Embassy Attacks and The Microwave Auditory Effect

If you’ve been paying attention to the news, you may have seen a series of articles coming out about US staffers in Cuba. It seems that 21 staffers have suffered a bizarre array of injuries ranging from hearing loss to dizziness to concussion-like traumatic brain injuries. Some staffers have reported hearing incapacitating sounds in the embassy and in their hotel rooms. The reports range from clicking to grinding, humming, or even blaring sounds. One staffer described being awoken to a horrifically loud sound, only to have it disappear as soon as he moved away from his bed. When he got back into bed, the mysterious sound came back.

Cuba has denied any wrongdoing. However, the US has already started to take action – expelling two Cuban diplomats from the US in May. The question though is what exactly could have caused these injuries. The press has gone wild with theories of sonic weaponry, hidden bugs, and electronic devices, poisons, you name it. Even Julian Assange has weighed in, stating “The diversity of symptoms suggests that this is a pathogen combined with paranoia in an isolated diplomatic corps.”

So what’s going on? Bizarre accidents? Cloak and dagger gone awry? Mass hysteria among the US state department, or something else entirely?

The most common theory passed around is some sort of auditory or sonic weapon. Acoustic (ultrasonic) non-lethal weapons like the Long Range Acoustic Device (LRAD) are well known due to their use by law enforcement to disperse protests, or on oceangoing ships to deter pirates and environmentalists. LRAD devices emit an extremely loud focused beam of sound. Usually, the sound is a siren, though the system can be used as a giant megaphone as well. Anyone in the beam is motivated to get out of it.

The thing about LRAD devices is they are not small or light. Even with ultrasonics, you can’t beat physics. Making a lot of noise means vibrating a lot of air. That takes a relatively big loudspeaker. The smallest portable device is roughly fifteen pounds. Since LRAD is still vibrating the air, it wouldn’t work very well through walls. LRAD style devices are also not very clandestine. They emit a beam 30 to 60 degrees wide, so definitely not a sound laser. They also have plenty of spill — operators standing behind the device always need to wear hearing protection.

Unwrap Your Tinfoil Hat

One theory I haven’t seen passed around much is the microwave auditory effect. This is a phenomenon where RF energy directed at a human head is converted to sound perceivable by the target. The first paper published about the effect was by Allan H. Frey in 1961. Frey worked at the General Electric advanced electronics center at Cornell University in NY.

I should note that microwave here refers to the wavelength of the RF signal being transmitted. Microwaves include any signal from 1-meter wavelength (300 MHz) to 3mm wavelength (100 GHz)

Images from Frey’s paper

Frey’s article describes how test subjects were able to hear buzzing, clicking, hisses and even knocking when transmitters were pointed at their skulls. Strangely, some of the test subjects were partially deaf, and still were able to hear the microwave sounds. What’s more, subjects could feel the effects from the microwave beam. Depending on the transmitter settings, subjects felt “severe buffeting of the head”. Further transmitter changes resulted in subjects reporting “pins and needles” sensations.

The purpose of the paper was to call attention to the phenomenon. Frey didn’t have the resources to completely explore the microwave auditory effect, so he wanted others to start working on it. It’s the scientific equivalent of saying “Hey, this is neat, you should check it out!”

If you haven’t guessed yet, the power levels required to hear microwave sounds were rather high. Frey used several transmitters at different power levels. The transmitters were pulsed, like magnetrons, so while average power was low, peak power was high.

As an example – the weakest transmitter Frey used was able to output a power density of 4 w/m² at 1310 Mhz. The peak power was 2670 w/m². The US guideline for human exposure at that frequency is 6.55 w/m². A different transmitter Frey used measured 71 w/m² at 425 MHz, with peaks at 2540 w/m². Compare this to the FCC guideline of 2 w/m² at that frequency.

What exactly causes the RF energy to be converted to sound? The mechanism behind the microwave auditory effect has not been scientifically proven. The leading theory is pulsed RF energy heats the tissues of the inner ear, causing them to expand quickly. These expansions cause tiny shockwaves which are then interpreted as sounds by the brain.

Frey noted that “one can shield, with 2-inch square piece of fly screen, a portion of the [temple] and completely cut off the RF sound.” Fly screen would be the fine metal grid used in screen doors. Frey may not have known it, but he was providing all the proof the tin-foil hat crowd needed.

Of course, a technology like this can’t exist without someone trying to build a weapon out of it. In the early 2000’s, the US Navy funded research on Mob Excess Deterrent Using Silent Audio (MEDUSA). This was a “less lethal weapon” which would use the microwave auditory effect for crowd control. It utilized an electronically steered antenna which allowed it to transmit a wide or narrow RF beam. MEDUSA could even “spotlight” multiple targets simultaneously.

MEDUSA never became a fieldable weapon. The initial results of the project were promising, but there were questions about its safety. At the high power levels used, could the micro shockwaves actually damage sensitive brain tissue? What about the RF exposure to sensitive neurons? The project was eventually canceled.

Coming back to the present day, could the microwave auditory effect be at play in Cuba? It’s quite possible. The technology is definitely there – the effect has been demonstrated with 1960’s era transmitters. With sufficient power and a narrow beam antenna, the attackers wouldn’t even need to be in the same room or building as their targets. Power levels high enough to be audible or even cause pain might also cause dizziness, nausea, and even traumatic brain injury. All we can do is wait for the results of the current investigations, and keep a tin foil hat handy.

Seek Out Scammers With Skimmer Scanner

Last week we reported on some work that Sparkfun had done in reverse engineering a type of hardware card skimmer found installed in gasoline pumps incorporating card payment hardware. The device in question was a man-in-the-middle attack, a PIC microcontroller programmed to listen to the serial communications between card reader and pump computer, and then store the result in an EEPROM.

The devices featured a Bluetooth module through which the crooks could harvest the card details remotely, and this in turn provides a handy way to identify them in the wild. If you find a Bluetooth connection at the pump bearing the right identification and with the right password, it can then be fingered as a skimmer by a simple response test. And to make that extra-easy they had written an app, which when we reported on it was available from a GitHub repository.

In a public-spirited move, they are now calling upon the hardware hacker and maker community to come together today, Monday, September 25th, and draw as much attention as possible to these devices in the wild, and with luck to get a few shut down. To that end, they have put a compiled version of the app in the Google Play Store to make it extra-easy to install on your phone, and they are asking for your help. They are asking for people to first read their tutorial linked above, then install the app and take it on the road. Then should any of you find a skimmer, please Tweet about it including your zip code and the #skimmerscanner hashtag. Perhaps someone with a bit of time on their hands might like to take such a feed of skimmer location data and map it.

It would be nice to think that this work might draw attention to the shocking lack of security in gas pumps that facilitates the skimmers, disrupt the finances of a few villains, and even result in some of them getting a free ride in a police car. We can hope, anyway.

Gasoline pump image: Michael Rivera [CC BY-SA 3.0].