If you live in a city, you’re constantly swimming in a thick soup of radio-frequency energy. FM radio stations put out hundreds of kilowatts each into the air. Students at the University of Washington, [Anran Wang] and [Vikram Iyer], asked themselves if they could harness this background radiation to transmit their own FM radio station, if only locally. The answer was an amazing yes.
The trailer video, embedded below, demos a couple of potential applications, but the paper (PDF) has more detail for the interested. Basically, they turn on and off an absorbing antenna at a frequency that’s picked so that it modulates a strong FM signal up to another adjacent channel. Frequency-modulating this backscatter carrier frequency adds audio (or data) to the product station.
One of the cooler tricks that they pull off with this system is to inject a second (stereo) channel into a mono FM station. Since FM radio is broadcast as a mono signal, with a left-minus-right signal sent alongside, they can make a two-channel stereo station by recreating the stereo pilot carrier and then adding in their own difference channel. Pretty slick. Of course, they could send data using this technique as well.
Why do this? A small radio station using backscatter doesn’t have to spend its power budget on the carrier. Instead, the device can operate on microwatts. Granted, it’s only for a few feet in any given direction, but the station broadcasts to existing FM radios, rather than requiring the purchase of an RFID reader or similar device. It’s a great hack that piggybacks on existing infrastructure in two ways. If this seems vaguely familiar, here’s a similar idea out of the very same lab that’s pulling off essentially the same trick indoors with WiFi signals.
So who’s up for local reflected pirate radio stations?
You’d think that with as many sick people as there are in the world, it wouldn’t be too difficult for a doctor in training to get practice. It’s easy to get experience treating common complaints like colds and the flu, but it might take the young doctor a while to run across a dissecting abdominal aortic aneurysm, and that won’t be the time for on the job training.
Enter the SP, or standardized patient – people trained to deliver information to medical students to simulate a particular case. There’s a problem with SPs, though. While it’s easy enough to coach someone to deliver an oral history reflecting a medical condition, the student eventually needs to examine the SP, which will reveal none of the signs and symptoms associated with the simulated case. To remedy this, [Chris Sanders] and [J Scott Christianson] from the University of Missouri developed an open-source RFID stethoscope to simulate patient findings.
This is one of those “why didn’t I think of that?” ideas. A cheap stethoscope is fitted with an Arduino, and RFID reader, and a small audio board. RFID tags are placed at diagnostic points over an SP’s chest and abdomen. When the stethoscope is placed over a tag, a specific sound file is fetched from an SD card and played over earbuds. The student doesn’t have to ask, “What am I hearing?” anymore – the actual sound of bruits or borborygmi are heard.
We can easily see expanding this system – RFID tags that trigger a faux ultrasound machine to display diagnostic images, or tiny OLED screens displaying tagged images into an otoscope. A good place to start expanding this idea might be this digital stethoscope recorder and analyzer.
Give kids some responsible and challenging tasks, and you’d be surprised at the results. The “Anything Goes” exhibit at the National Museum in Warsaw was aimed as a museological and educational experiment. A group of 69 children aged 6–14 was divided into teams responsible for preparing the main temporary exhibition at the museum. Over six months, they worked on preparing the exhibition during weekly four-hour meetings. They prepared scripts, provided ideas for multimedia presentations, and curated almost 300 works for display. One of those was [Robert Mordzon]’s Giant Interactive Crossword.
The build is in two parts. The letter tiles, which have embedded RFID tags, obviously look like the easiest part of the build. The table, looking at the video (after the break), probably needed a lot more effort and labour. It is built in two halves to make construction easier. There are a 130 boxes that need to be filled in with the right letters to complete the crossword. Each box contains a bunch of electronics consisting of an Arduino Nano, a RFID Reader and a bunch of sixteen WS2812B LEDs, all assembled on a custom PCB. Do the math, and you’ll figure out that there’s 2080 LEDs, each capable of sipping 60 mA at full brightness. That’s a total current requirement of almost 125 amps at 5 V. Add in all the Arduino’s, and [Robert] needed a beefy 750 W of power, supplied via four switch mode power supplies.
Each Arduino Nano is a slave on the I²C bus. The I²C master is an Arduino Mega 2560, which in turn communicates with a computer over serial. When a box is empty, the LEDs are dim, when a wrong letter is placed, they turn Red, and when the right letter is placed, they turn Green. If a word gets completed, a special word animation is played. This information is also passed on to the computer, which then projects an animation related to the word on a giant wall screen. Upon the crossword getting completed, the table erupts in to a sound (via the computer) and light “disco” show and also reveals the main motto of this section of the exhibit – “Playing the Hero”.
How often do you see problems that need fixing? How often do you design your own solutions to them — even if they won’t be implemented at scale? Seeing that many of the municipal parking lots in his native Sri Lanka use a paper ticketing system which is prone to failure, [Shazin Sadakath] whipped up his own solution: an efficient RFID tag logging system.
Group entry hacks are a favorite for hacker social groups. Why use old fashioned keys when you can use newfangled electronic keys? If you are looking to build a simple RFID-based security system to secure your important stuff, this project from Resin.io is a good place to start. In it, [Joe Roberts] outlines the process of building a simple RFID-triggered mechanism for their office door.
It’s a pretty simple setup that is composed of an RFID reader, a Rasperry Pi and a Neopixel ring. When someone places an RFID card against the reader hidden behind a poster by their front door, the reader grabs the code and the Pi compares it with a list of authorized users. If the card is on the list, the Pi triggers the door lock using a signal line originally designed to work with an intercom system. If the user isn’t on the list, a laser is triggered that vaporizes the interloper… well, that’s perhaps in the next version, along with an API that will allow someone to open the door from the company chat application.
At the moment, this is a clean, simple build that uses only a few cheap components, but which could be the basis for a more sophisticated security system in the future.
Anyone who has worked in an office with a vending machine knows this problem well: someone wants a snack or a drink from the vending machine, but doesn’t have any small change. So, they proceed to walk around the office trying to find someone to make some change for them. It’s a hassle, and a surprisingly common one. Sure, a lot of vending machines now accept credit cards, but they’re still in the minority.
This was the problem facing Belgium-based automation company November Five. As automation and IoT specialists, their first thought was to hack the vending machine itself. But, unfortunately, they didn’t own it; as many of you know, vending machines are generally owned by the distributor. So, they needed a solution that allowed their employees access to the vending machine, without actually modifying the vending machine itself.
The solution they came up with was to attach an RFID-activated coin dispenser to the vending machine. Everyone at the company already has an RFID badge for opening doors and such, so the system wouldn’t add any burden to the employees. And keeping track of how many coins each employee used was a simple task of logging requests.
A mass participation sporting event such as a road race presents a significant problem for its record keepers. It would be impossible to have ten thousand timekeepers hovering over stopwatches at the finish line, so how do they record each runner’s time? The answer lies in an RFID chip attached to the inside of the bib each runner wears, which is read as the runner crosses the line to ensure that their time is recorded among the hundreds of other participants.
Stripping away the foam covering of the RFID assembly revealed a foil antenna for the 860-960MHz UHF band with the tiny RFID chip at its centre. The antenna is interesting, it’s a rather simple wideband dipole folded over with what looks like a matching stub arrangement and an arrow device incorporated into the fold that is probably for aesthetic rather than practical purposes. He identified the chip as an Impinj Monza 4, whose data sheet contains reference designs for antennas we’d expect to deliver a better performance.
After some trial-by-fire epoxy removal the tiny chip was revealed and photographed. It’s a device of three parts, the power scavenging and analog radio section, the non-volatile memory that carries the payload, and a finite-state logic machine to do the work. This isn’t a proper processor, instead it contains only the logic required to do the one task of returning the payload.
He finishes off with a comparison photograph of the chip — which is about the size of a grain of salt — atop a 1980s 8051-series microcontroller to show both its tiny size and the density advancements achieved over those intervening decades.
Since RFID devices are becoming a ubiquitous part of everyday life it is interesting to learn more about them through teardowns like this one. The chip here is a bit different to those you’ll find in more mundane applications in that it uses a much higher frequency, we’d be interested to know the RF field strength required at the finish line to activate it. It would also be interesting to know how the system handles collisions, with many runners passing the reader at once there must be a lot of RFID chatter on the airwaves.