$2 FM Transmitter For Raspberry Pi

November 12, 2014 by Elliot Williams 37 Comments

We love re-purposed consumer gear. This project uses a cheap, discontinued cellphone gadget to create a Raspberry Pi controlled FM radio transmitter.

The Sony-Ericsson MMR-70 radio transmitter apparently used to connect to a cell phone and broadcast music. But the Walkman cellphones in question are a little bit old in the tooth, so one can buy the transmitter units for cheap on the resale market. What makes the transmitters even more interesting is that you can activate and deactivate the radio, change frequency or output power, and even send RDS station and song information.

It turns out (link in German) that the radios have an AVR ATMega32 microcontroller and a NS73 radio transmitter module, which can be entirely controlled over I2C. (Schematic here as PDF.) The units also have handy test points strewn all around. Once the test points were mapped out, one could completely ignore the on-board AVR microcontroller and control the FM transmitter module directly using the Raspberry Pi’s I2C outputs.

And that’s where [Manawyrm] stepped in. She wrote an I2C daemon for the Raspberry Pi that lets you control the FM transmitter via simple commands. All you have to do is solder up a bunch of test points, install [Manawyrm]’s software, write a batch script, and you’re on the air. For instance, this makes building a FM radio retransmitter for online streamed audio a one-day project. You can see his working example on youtube. Of course, you’ll want a web-based remote control interface to go with that.

If you’re interested in hacking along, and don’t have a Raspberry Pi application in mind, Sparkfun used to sell the NS73 radio transmitter so you can find lots of good information about the chip. We’d love to see a stand-alone broadcasting gizmo that actually utilizes the onboard AVR chip, but our hats are off to [Manawyrm] for making the Raspberry Pi version so accessible.

Transmitting Data Long-Distance With Morse Code

November 12, 2014 by Ethan Zonca 61 Comments

[Konstantinos] wrote in to tell us about his CDW project: a digital encoding scheme for ham radio that uses CW (continuous wave) Morse code for digital data transfer. [Link updated 1/5/16] CW operation with Morse code is great for narrow-bandwidth low-speed communication over long distances. To take advantage of this, [Konstantinos] developed a program that takes binary or text files, compresses them, and translates them to a series of letters and numbers that can be represented with Morse code.

The software translates the characters into sequences of Morse code pulses, and plays an audio stream of the result. His software doesn’t support decoding Morse from an audio stream, so [Konstantinos] recommends using one of many existing programs to get the job done. Alternatively those with a good ear and working knowledge of Morse can transcribe the characters by hand.

After receiving a broadcast, the user pastes received characters back in the software. The software re-assembles the binary file from the Morse characters and decompresses the result. [Konstantinos] also added a simple XOR encryption feature, but keep in mind that using encryption on ham radio bands is technically illegal.

Fox Hunting With A Raspberry Pi

November 6, 2014 by Bryan Cockfield 11 Comments

No, not a real fox! [KM4EFP] is a ham radio operator with a passion for fox hunting, which is an event where several radio operators attempt to find a broadcasting beacon (a “fox”) using radio direction finding techniques. [KM4EFP] has just built his own portable fox using a Raspberry Pi in a very well-built enclosure.

Since the fox could be outside for a while, the project was housed in a reasonably weatherproof ammunition case. A mount for an antenna was attached to the side, and it is hooked up to a GPIO pin on the Raspberry Pi. The entire device is powered by a 6000 mAh battery pack which allows the fox to broadcast long enough to be found.

The software running on the Raspberry Pi is very similar to the Pi FM transmitter program but it is specially made for ham radio broadcasting instead. Almost no extra hardware is needed to get the Pi broadcasting radio, as these software packages can drive the antenna directly from the GPIO pin. This is a great twist on the standard FM transmitter that ham radio enthusiasts everywhere can use to start finding those wily foxes!

SDR: Satellite Death Receiver

November 4, 2014 by Kristina Panos 18 Comments

Halloween may be over, but [happysat] has found a way to listen to the dead. Satellites, that is, specifically those in the 136-138 MHz and 150-400 MHz ranges. He’s using an RTL-SDR dongle and a QFH antenna to detect the death throes of decommissioned navigation and space research satellites.

[happysat] was listening to NOAA/Meteor on the 137MHz band when he made this discovery. When a satellite is near end of life, the last bit of fuel is used to push it into graveyard orbit. This doesn’t always work, however, and when the light is just right, a chemical reaction makes the long-dead batteries conduct and these satellites in purgatory transmit once more.

They’re not sending out anything ~~proprietary~~ useful, just unmodulated carrier that sometimes interferes with currently operational satellites on the 136-138 MHz band. [happysat] captured some audio from two of the oldest satellites that are still broadcasting, and links to a TLE set of dead satellites he created. Check out his frequency database for SDR# as well. Don’t have a weather satellite-capable antenna? Build one!

[via /r/RTLSDR]

The Internet Of Things Chip Gets A New Spectrum

October 20, 2014 by Brian Benchoff 52 Comments

Last year we learned about Weightless, an Internet of Things chip that solves all the problems of current wireless solutions. It’s low power and has a 10-year battery life (one AA cell), the hardware should cost around $2 per module, and the range of the Weightless devices range from 5+km in urban environments to 20-30km in rural environments. There haven’t been many public announcements from the Weightless SIG since the specification was announced, but today they’re announcing Weightless will include an additional spectrum, the 868/915 MHz ISM spectrum.

The original plan for Weightless was to use the spectrum left behind by UHF TV – between 470 and 790MHz. Regulatory agencies haven’t been moving as fast as members of the Weightless SIG would have hoped, so now they’re working on a slightly different design that uses the already-allocated ISM bands. They’re not giving up on the TV whitespace spectrum; that’s still part of the plan to put radio modules in everything. The new Weightless-N will be available sooner, though, with the first publicly available base station, module, and SDK arriving sometime next spring.

Weightless has put up a video describing their new Weightless-N hardware; you can check that out below. If you want the TL;DR of how Weightless can claim such a long battery life and huge range from an Internet of Things radio module, here’s an overly simplified explanation: power, range, and bandwidth. Pick any two.

Continue reading “The Internet Of Things Chip Gets A New Spectrum” →

Hacklet 19 – Ham Radio

October 17, 2014 by Adam Fabio 20 Comments

Amateur, or ham radio operators have always been hackers. For much of the early 1900’s, buying a radio was expensive or impossible. Hams would build their own rigs, learning electronics and radio theory along the way. Time moves on, but hams keep hacking. Today we’re highlighting some of the best ham radio projects on Hackaday.io!

We start with [DainBramage1991] and his very practical RTL-SDR With Upconverter and Case. [DainBramage1991] fell in love with his low-cost RTL software defined radio dongle. He even added a Ham-It-Up upconverter to cover HF bands. The only problem was RF noise. the Realtek USB sticks tend to have little or no filtering, which means they are very susceptible to noise. [DainBramage1991] used the time-honored technique of insulating with copper clad board. Bits of PCB hold the RTL-SDR and upconverter in place. More PCB separates the two boards. Everything goes into a steel enclosure which keeps that unwanted RF at bay.

Next up is [Ryan Miller’s aka KG7HZQ]’s ham radio fox hunt attenuator. Ham radio fox hunt’s don’t involve baying dogs or horses. In this case a fox hunt is a contest to find hidden low power transmitters. If you’ve never tried one, it’s a heck of a lot of fun. One of the challenges with a fox hunt is to find the direction to the transmitter when you’re very close. Even with directional antennas, reflections and swamped receivers make it hard to figure out just where the transmitter is. The solution is an attenuator, which simply reduces the signal to a more reasonable value. [Ryan] also used copper clad PCB for his circuit. Since the attenuator parts are soldered directly to the PCB, this is more of a Manhattan style design. Two ceramic 1k pots help him achieve his goal of near perfect linear attenuation. We’re betting this attenuator will help [Ryan] win some contests!

Who says amateur radio won’t take you places? It may well be taking [Michael R Colton] to space! [Michael’s] project PortableSDR is one of the five finalists in The Hackaday Prize. We covered Michael earlier in the contest. PortableSDR started as a ham radio project: a radio system which would be easy for hams to take with them on backpacking trips. It’s grown into so much more now, with software defined radio reception and transmission, vector network analysis, antenna analysis, GPS, and a host of other features. We seriously love how [Michael] optimized a small LCD for waterfall display, tuning, and bandpass filter adjustment.

[W5VO] is working on an Ethernet to Radio Adapter. Every foot of coax in a radio system loses signal. Connections are even worse. It can all add up to several dB loss. [W5VO] wants to put an SDR at the antenna feed-point. With the signal path minimized, more watts make it out when transmitting, and more signal gets back to the receiver when listening. The interface between the SDR and host computer will be all digital; Ethernet to be precise. [W5VO] isn’t the first person to do something like this, microwave systems have had the transmitter and LNB at the antenna for years. That doesn’t take away from [W5VO’s] design at all He’s been quiet for a while, but we’re hoping he continues on his design!

Where is everyone else? We’re a bit light on projects this week, but we have a good reason. There just aren’t enough ham radio projects on Hackaday.io! We’re hoping to change that though. Are you an amateur radio enthusiast? Document your project on the site. Get input from other hams and push the envelope! You might even find yourself on the Ham Radio List!

That’s all for this episode of The Hacklet. As always, QRX is next week. Same hack time, same hack channel, bringing you the best of Hackaday.io! 73’s!

Digital “Crystal” Breathes New Life Into Old Radio

October 15, 2014 by Elliot Williams 11 Comments

[Bill Meara] of the Soldersmoke Podcast has a nice old Drake 2B radio, and wanted to use it for the 12 meter amateur band. These old radios normally make switching tuning bands easy — you just swap out one frequency crystal for another and you’re set.

Only [Bill] didn’t have the 21 MHz crystal that he needed. No problem, because he had a junk crystal, a hacksaw, and a modern direct-digital synthesis (DDS) chip sitting around. So he takes the donor crystal, cuts it open, and solders the two wires directly from the DDS to the crystal’s pins. Now he’s got a plug-in replacement digital oscillator that doesn’t require modifying the nice old Drake receiver at all. A sweet little trick.

The video’s a little bit long, but the money shot comes in around 5:00.

Now, one might worry about simply plugging a powered circuit (the DDS) in place of a passive element (the crystal), but it seems to work and the proof of the pudding is in the tasting. We wonder how far this digitally-controlled-analog-receiver idea could be extended.