Reading 2.4GHz Transmitters With An Arduino

QuadThere are a lot of cheap quadcopter kits out there, sold ready to fly with a transmitter and battery for right around $50 USD. One of the more popular of these micro quads is the V2X2 series. They are, unfortunately not compatible with any other radio protocol out there, but [Alexandre] has managed to use the transmitter included with his V202 quad to send data to an Arduino.

Like most quads, the transmitter that came with [Alexandre]‘s V202 operates on 2.4GHz. Listening in on that band required a little bit of hardware, in this case a nordic Semiconductors nRF24L01p. Attached to this chip is a regular ‘ol Arduino running a bit of code that includes [Alexandre]‘s V202 library.

Right now, the build can detect if the quad is bound or not, and read the current position of the throttle, yaw, pitch, and roll, as well as all the associated trims. It’s just the beginnings of [Alexandre]‘s project, but his eventual goal is to build an Arduino bot based on the code, complete with RC servos. Not bad for a transmitter that will be utterly useless when the microquad eventually breaks.

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DIY Ultra Wideband Impulse Synthetic Aperture Radar And A MakerBot


What could possibly be better than printing out a few low-resolution voxels on a MakerBot? A whole lot of things, but how about getting those voxels with your own synthetic aperture radar? That’s what [Gregory Charvat] has been up to, and he’s documented the entire process for us.

The build began with an ultra wideband impulse radar we saw a while ago. The radar is built from scraps [Greg] picked up on eBay, and is able to image a scene in the time domain, creating nice linear sweeps on a MATLAB plot when [Greg] runs in front of the horns.

With an impulse radar under his belt, [Greg] moved up the technological ladder to something that can produce vaguely intelligible images with his setup. The synthetic aperture radar made from putting his radar horns on the carriage of a garage door opener. The horns slowly scan back and forth along the linear rail, taking single impulse readings and adding them together in an image. In the video below, [Greg] is able to image a few pieces of copper pipe only a few inches in diameter. The necessary equipment for this build only cost [Greg] a few hundred bucks at the Dayton Hamvention, and a similar setup could be put together for even less.

If building an X band impulse synthetic aperture radar isn’t impressive enough. [Greg] also 3D printed one of his radar images on a MakerBot. That’s just applying stlwrite to the 2D radar image and feeding it into MakerWare. Gotta have that blog cred, doe. It also makes for the best headline I’ve ever written.

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Airchat, The Wireless Mesh Network From Lulzlabs


With the lessons learned from the Egyptian, Libyan, and Syrian revolutions, a few hardware and software hackers over at Lulzlabs have taken it upon themselves to create a free-as-in-beer and free-as-in-speech digital communications protocol that doesn’t deal with expensive, highly-surveilled commercial and government controlled infrastructure. They call it Airchat, and it’s an impressive piece of work if you don’t care about silly things like ‘laws’.

Before going any further, we have to say yes, this does use amateur radio bands, and yes, they’re using (optional) encryption, and no, the team behind Airchat isn’t complying with all FCC and other amateur radio rules and regulations. Officially, we have to say the FCC (and similar agencies in other countries) have been granted the power – by the people – to regulate the radio spectrum, and you really shouldn’t disobey them. Notice the phrasing in that last sentence, and draw your own philosophical conclusions.

Airchat uses an off the shelf amateur transmitter, a Yaesu 897D in the example video below although a $30 Chinese handheld radio will do, to create a mesh network between other Airchat users running the same software. The protocol is based on the Lulzpacket, a few bits of information that give the message error correction and a random code to identify the packet. Each node in this mesh network is defined by it’s ability to decrypt messages. There’s no hardware ID, and no plain text transmitter identification. It’s the mesh network you want if you’re under the thumb of an oppressive government.

Airchat has already been used to play chess with people 180 miles away, controlled a 3D printer over 80 miles, and has been used to share pictures and voice chats. It’s still a proof of concept, and the example use cases – NGOs working in Africa, disaster response, and expedition base camps – are noble enough to not dismiss this entirely.

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ISEE-3 Dream Team Needs Your Help

ISEE-3 Moon flyby

The mission to save ISEE-3 has is underway. The ISEE-3 Reboot Project has posted a crowdfunding campaign on Rockethub. When we first covered the ISEE-3 story no one had heard from it since 2008. Since then AMSAT-DL, an amateur radio group in Germany has received signals from the probe.

The ISEE-3 Reboot Project is being managed by [Dennis Wingo] and [Keith Cowing], the same two men who spearheaded the effort to recover NASA’s Lunar Orbiter images from old magnetic tapes. They did most of their work using restored 1960’s equipment in a vacant McDonald’s.

The goal of the ISEE Reboot Project is to return ISEE-3 to its original Earth/Sun Lagrange point L1 orbit. Once safely back in orbit, it will be used for STEM education, amateur radio solar predictions, and for science about the sun. In [Dennis Wingo's] own words

If we can do this, we will have an open source, publicly accessible satellite data stream of the first open source satellite above Low Earth Orbit.

[Wingo] and [Cowing] aren’t alone in this effort; they are working with a venerable dream team. In addition to getting the nod from NASA, the team also has the help of [Dr. Robert Farquhar], the orbital dynamics guru who originally designed ISEE-3’s comet intercept orbit . [Farquhar] has an extremely personal reason to participate in this project. In 1982 he “borrowed” the satellite to go comet hunting. Once that mission was complete, he promised to give ISEE-3 back. [Dr. Farquhar] and his team designed the maneuvers required to bring ISEE-3 back to L1 orbit back in the 1980’s. This includes a breathtaking moon flyby at an altitude of less than 50 km. Seriously, we want to see this guy’s KSP missions.

Communicating with the ISEE-3 is going to take some serious power and antenna gain. The project has this in the form of a 21 meter dish at Moorehead State University in Kentucky, USA, and the Arecibo Observatory. Arecibo should be well-known to our readers by now. Moorehead and Arecibo have both received signals from ISEE-3. The reboot project team is also working directly with the AMSAT-DL team in Germany.

If this effort seems a bit rushed, that’s because time is very short. To implement [Dr. Farquhar's] plan, ISEE-3 must fire its thrusters by late June 2014. In just two months the team needs to create software to implement ISEE-3’s communications protocols, obtain and install transmitters at Moorehead and Aricibo, and send some basic commands to the craft. Only then can they begin to ascertain ISEE-3’s overall health in preparation for a thruster burn.

If  the ISEE-3 Reboot Project succeeds, we’ll have an accessible satellite well outside of low Earth orbit. If it fails, Issac Newton will remain at the helm. ISEE-3 will fly right past Earth, not to be seen again until August 2029.

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Building A Software Defined Radio With A Teensy


[Rich, VE3MKC] has been wanting to get into Software Defined Radio for a while now, but didn’t want to go the usual PC route. He initially thought the Raspberry Pi would be the best platform for a small, embedded device that could manipulate audio, but after discovering the ARM-powered Teensy 3.0, had an entirely different project in mind.

[Rich] is using a SoftRock SDR to take RF from an antenna and downconvert it into the audio range. Doing DSP for SDR is fairly computationally intensive, but he found a Teensy 3.0 with the audio adapter board was more than up to the task.

So far, [Rich] is running the audio from the SoftRock to the Teensy where the audio is digitized and multiplied with a VFO, sent through a filter and then sent to the output of the headphone jack to a speaker. The volume pot on the audio adapter board is used to tune the VFO, something [Rich] be replacing with a proper encoder sometime in the future.

In the videos below, you can see [Rich] listening in on a contest with a tiny TFT display showing everybody on the air. It’s a very cool build, and even though it’s still very early in development, there’s still a whole lot of CPU cycles for the Teensy to do some very cool stuff.

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[Balint]‘s GNU Radio Tutorials


[Balint] has a bit of history in dealing with software defined radios and cheap USB TV tuners turned into what would have been very expensive hardware a few years ago. Now [Balint] is finally posting a few really great GNU Radio tutorials, aimed at getting software defined radio beginners up and running with some of the coolest hardware around today.

[Balint] is well-known around these parts for being the first person to create a GNU Radio source block for the implausibly inexpensive USB TV tuners, allowing anyone with $20 and enough patience to wait for a package from China to listen in on everything from 22 to 2200 MHz. There’s a lot of interesting stuff happening in that band, including the ACARS messages between airliners and traffic control, something that allowed [Balint] to play air traffic controller with a minimal amount of hardware.

Right now the tutorials are geared towards the absolute beginner, starting at the beginning with getting GNU Radio up and running. From there the tutorials continue to receiving FM radio, and with a small hardware investment, even transmitting over multiple frequencies.

It’s not much of an understatement to say software defined radio is one of the most versatile and fun projects out there. [Balint] even demonstrated triggering restaurant pagers with a simple SDR project, a fun project that is sure to annoy his coworkers.

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Unlocking your Computer with a Leonardo and an NFC Shield

Manually typing your login password every time you need to login on your computer can get annoying, especially if it is long and complex. To tackle this problem [Lewis] assembled an NFC computer unlocker by using an Arduino Leonardo together with an NFC shield. As the latter doesn’t come with its headers soldered, a little bit of handy work was required.

A custom enclosure was printed in order to house the two boards together and discretely mount them under a desk for easy use. Luckily enough very few code was needed as [Lewis] used the Adafruit NFC library. The main program basically scans for nearby NFC cards, compares their (big-endianned) UIDs against a memory stored-one and enters a stored password upon match. We think it is a nice first project for the new generation of hobbyists out there. This is along the same lines as the project we saw in September.

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