Send Wireless TXT between Two TI Calculators

 

TI calculators with wireless circuitry

One day while sitting in class in a Cornell University schoolroom, [Will] and [Michael] thought how cool it would be to send text messages to each other via their Texas Instruments calculators.  Connecting the two serial ports with a serial cable was out of the question. So they decided to develop a wireless link that would work for both TI-83 and TI-84 calculators.

The system is powered by a pair of ATmega644’s and two Radiotronix RF Modules that creates a wireless link between the two serial ports. The serial ports are 3 wire ports, which can be used for several things, including acting as a TV out port. [Will] and [Michael] reverse engineered the port’s protocol and did an excellent job at explaining it in full detail. Because they are dealing with the lowest level of the physical protocol, there is no need for them to deal with higher levels like checksums, header packets, ext.

Be sure to stick around after the break to see a video of the project in action. It’s quite slow for today’s standards. If you have any ideas on how to speed it up, be sure to let everyone know in the comments.

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Sniping 2.4GHz

sniper

A long time ago when WiFi and Bluetooth were new and ‘wardriving’ was still a word, a few guys put a big antenna on a rifle and brought it to DefCon. Times have changed, technology has improved, and now [Hunter] has built his own improved version.

The original sniper Yagi was a simple device with a 2.4 GHz directional antenna taped onto the barrel, but without any real computational power. Now that displays, ARM boards, and the software to put this project all together are cheap and readily available, [Hunter] looked towards ubiquitous computing platforms to make his Sniper Yagi a little more useful.

This version uses a high gain (25dBi) antenna, a slick fold-out screen, and a Raspberry Pi loaded up with Raspberry Pwn, the pentesting Raspi distro, to run the gun. There’s a button connected to the trigger that will automatically search the WiFi spectrum for the best candidate for cracking and… get cracking.

[Hunter] says he hasn’t taken this highly modified airsoft rifle outside, nor has he pointed out a window. This leaves us with the question of how he’s actually testing it, but at least it looks really, really cool.

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

box01

 

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.