66% or better

Measuring Frequency Response with an RTL-SDR Dongle and a Diode

[Hans] wanted to see the frequency response of a bandpass filter but didn’t have a lot of test equipment. Using an RTL-SDR dongle, some software and a quickly made noise generator, he still managed to get a rough idea of the filter’s characteristics.

How did he do it? He ‘simply’ measured his noise generator frequency characteristics with and without the bandpass filter connected to its output and then subtracted one curve with the other. As you can see in the diagram above, the noise generator is based around a zener diode operating at the reverse breakdown voltage. DC blocking is then done with a simple capacitor.

Given that a standard RTL-SDR dongle can only sample a 2-3MHz wide spectrum gap at a time, [Hans] used rtlsdr-scanner to sweep his region of interest. In his write-up, he also did a great job at describing the limitations of such an approach: for example, the dynamic range of the ADC is only 48dB.

Building a Mesh Networked Conference Badge

[Andrew] just finished his write-up describing electronic conference badges that he built for a free South African security conference (part1, part2). The end platform shown above is based on an ATMega328, a Nokia 5110 LCD, a 433MHz AM/OOK TX/RX module, a few LEDs and buttons.

The badges form a mesh network to send messages. This allows conversations between different attendees to be tracked. Final cost was the main constraint during this adventure, which is why these particular components were chosen and bought from eBay & Alibaba.

The first PCB prototypes were CNC milled. Once the PCB milling was complete there was a whole lot of soldering to be done. Luckily enough [Andrew]‘s friends joined in to solder the 77 final boards. He also did a great job at documenting the protocol he setup, which was verified using the open source tool Maltego. Click past the break to see two videos of the system in action.

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Step Into the Ring with Fight Coach

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As MMA continues to grow in popularity, the competition is getting tougher. There’s always someone else out there who’s training harder and longer than you are. So how do you get the advantage over your competitors? More push-ups? Sit-ups? Eat more vegetables? What about installing custom 2 by 1 inch, 5 gram PCB’s armed with an ATmega32U4, a MPU-6050 6 axis accelerometer and an RN-41 Bluetooth module into each of your gloves? Now that’s what we’re talking about.

[Vincent] and [Jooyoung] of Cornell joined their classmates in turning out another cool piece of electrical engineering. Fight Coach records data from the fighter’s gloves so that it can not only be analyzed to improve performance, but also interact with the fighter in real-time.  Though not quite as immersive as some fighter training techniques we’ve seen, Fight Coach might just give a fighter a slight edge in the ring.

Fight Coach offers 3 modes of training: Defense mode, Damage mode and Free-Training mode. As usual with Cornell projects, all code, schematics and a wealth of information on the project is just a click away. And stick around after the break for a video demonstration of Fight Coach.

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Extracting Gesture Information from Existing Wireless Signals

A team at the University of Washington recently developed Allsee, a simple gesture recognition device composed of very few components. Contrary to conventional Doppler modules (like this one) that emit their own RF signal, Allsee uses already existing wireless signals (TV and RFID transmissions) to extract any movement that may occur in front of it.

Allsee’s receiver circuit uses a simple envelope detector to extract the amplitude information to feed it to a microcontroller Analog to Digital Converter (ADC). Each gesture will therefore produce a semi-unique footprint (see picture above).  The footprint can be analyzed to launch a dedicated action on your computer/cellphone. The PDF article claims that the team achieved a 97% classification accuracy over a set of eight gestures.

Obviously the main advantage of this system is its low power consumption. A nice demonstration video is embedded after the break, and we’d like to think [Korbi] for tipping us about this story.

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Sniffing pH Sensor RF Signals for Feedback Re: Your Esophagus

For about a week [Justin] had a wireless acidity level sensor in his esophagus and a pager-looking RF receiver in his pocket. So he naturally decided to use an RTL-SDR dongle to sniff the signals coming out of him. As most of our Hackaday readers know, these cheap RTL2382U-based DVB-T receivers are very handy when it comes to listening to anything between 50MHz and 1800MHz. [Justin] actually did a great job at listing all the things these receivers can be used for (aircraft traffic monitoring, weather images download, electric meter reading, pacemaker monitoring…).

After some Googling he managed to find his Bravo pH sensor user’s guide and therefore discovered its main frequency and modulation scheme (433.92MHz / ASK). [Justin] then used gqrx and Audacity to manually decode the packets before writing a browser-based tool which uses an audio file. Finally, a few additional hours of thinking allowed him to extract his dear esophagus’ pH value.

Atmel Announces SmartConnect WiFi Modules

Atmel SmartConnect

This week we talked with Atmel about their new WiFi solutions targeting Internet of Things applications. Back in 2012, Atmel acquired Ozmo, a company focused on point-to-point WiFi solutions using WiFi Direct. These devices are known as SmartDirect, and have been available for some time.

Atmel has just announced a new product line: SmartConnect. This moves beyond the point-to-point nature of WiFi Direct, and enables connections to standard access points. The SmartConnect series is designed for embedding in low cost devices that need to connect to a network.

The first devices in the SmartConnect line will be modules based on two chips: an Atmel SAMD21 Cortex-M0+ microcontroller and an Ozmo 3000 WiFi System on Chip. There’s also an on-board antenna and RF shielding can. It’s a drop in WiFi module, which is certified by the FCC. You can hook up your microcontroller to this device over SPI, and have a fully certified design that supports WiFi.

There’s two ways to use the module. The first is as an add-on, which is similar to existing modules. A host microcontroller communicates with the module over SPI and utilizes its command set. The second method uses the module as a standalone device, with application code running on the internal SAMD21 microcontroller. Atmel has said that the standalone option will only be available on a case to case basis, but we’re hoping this opens up to everyone. If the Arduino toolchain could target this microcontroller, it could be a great development platform for cheap WiFi devices.

SmartConnect Architectures

The Add-On and Standalone Architectures

At first glance, this module looks very similar to other WiFi modules, including the CC3000 which we’ve discussed in the past. However there are some notable differences. One major feature is the built in support for TLS and HTTPS, which makes it easier to build devices with secure connections. This is critical when deploying devices that are connected over the internet.

Atmel is claiming improvements in power management as well. The module can run straight from a battery at 1.8 V to 3.3 V without external regulation, and has a deep sleep current of 5 nA. Obviously the operating power will be much higher, but this will greatly assist devices that sporadically connect to the internet. They also hinted at the pricing, saying the modules will come close to halving the current price of similar WiFi solutions. SmartConnect is targeting a launch date of June 15, so we hope to learn more this summer.

We’re always excited to see better connectivity solutions. If Atmel comes through with a device allowing for cheaper and more secure WiFi modules, it will be a great part for building Internet of Things devices. With a projected 50 billion IoT devices by 2020, we expect to see a lot of progress in this space from silicon companies trying to grab market share.

PCB Antenna Reference Designs

PCB Antenna

Have you ever built a wireless project and weren’t sure how to make one of those awesome (and cheap!) PCB antennas? “What low-cost solutions does our Antenna Board #referencedesign contain?” said Texas Instruments (TI) recently via Twitter.  This older reference design contains some comprehensive designs for sub-1 GHz and 2.4 GHz antennas.

While TI’s documentation can be difficult to navigate, there are many hidden gems, and this is one of them. While TI created these designs for use with their wireless products, they will work on any device which utilizes the same wireless base frequency. For example, you could use any of the 2.4 GHz antennas with any Bluetooth, WiFi (2.4 GHz), or Bluetooth Low Energy chips. Simply open up their Antenna Selection Quick Guide document and navigate to the specific design for whichever antenna you would like to build.

For a more detailed overview of what goes into designing and testing a PCB antenna, check out this hack which we featured back in 2010. With the internet of things coming into its own, wireless projects will become more and more prolific, making PCB antennas more important than ever.