Spark Gap and Coherer Meet Beagle Bone

Getting back to basics is a great way to teach yourself about a technology. We see it all the time with computers built from NAND gates or even discrete transistors. It’s the same for radio – stripping it back to the 19th century can really let you own the technology. But if an old-school wireless setup still needs a 21st-century twist to light your fire, try this spark gap transmitter and coherer receiver with a Beagle Bone Morse decoder.

At its heart, a spark gap transmitter is just a broadband RF noise generator, and as such is pretty illegal to operate these days. [Ashish Derhgawen]’s version, which lacks an LC tuning circuit, would be especially obnoxious if it had an antenna. But even without one, the 100% electromechanical transmitter is good for a couple of feet –┬ámore than enough for experimentation without incurring the wrath of local hams.

The receiver is based on a coherer, a device that conducts electricity only when a passing radio wave disturbs it. [Ashish]’s coherer is a slug of iron filings between two bolts in a plastic tube. To reset the coherer, [Ashish] added a decoherer built from an electromagnetic doorbell ringer to tap the tube and jostle the filings back into the nonconductive state. He also added an optoisolator to condition the receiver’s output for an IO pin on the Beagle, and a Python script to decode the incoming Morse. You can see it in action in the video below.

If this build looks familiar, it’s because we’ve covered [Ashish]’s efforts before. But this project keeps evolving, and it’s nice to see where he’s taken it and what he’s learned – like that MOSFETs don’t like inductive kickback much.

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Introducing the BeagleBone Blue

The BeagleBone is a board that doesn’t get a lot of attention in a world of $5 Raspberry Pis, $8 single board computers based on router chipsets, and a dizzying array of Kickstarter projects promising Android and Linux on tiny credit card-sized single board computers. That doesn’t mean the BeagleBone still isn’t evolving, as evidenced by the recent announcement of the BeagleBone Blue.

The BeagleBone Blue is the latest board in the BeagleBone family, introduced last week at CES. The Blue is the result of a collaboration between UCSD Engineering and TI, and with that comes a BeagleBone built for one specific purpose: robotics and autonomous vehicles. With a suite of sensors very useful for robotics and a supported software stack ideal for robots and drones, the BeagleBone Blue is the perfect board for all kinds of robots.

On board the BeagleBone Blue is a 2 cell LiPo charger with cell balancing and a 6-16 V charger input. The board also comes with eight 6V servo outputs, four DC motor outputs and inputs for four quadrature encoders. Sensors include a nine axis IMU and barometer. Unlike all previous BeagleBones, the BeagleBone Blue also comes with wireless networking: 802.11bgn, Bluetooth 4.0 and BLE. USB 2.0 client and host ports are also included.

Like all of the recent BeagleBoards, including the recently released BeagleBone Green, the Blue uses the same AM3358 1 GHz ARM Cortex 8 CPU, features 512 MB of DDR3 RAM, 4GB of on board Flash, and features the main selling point of the BeagleBoard, two 32-bit programmable real-time units (PRUs) running at 200 MHz. The PRUs are what give the BeagleBone the ability to blink pins and control peripherals faster than any other single board Linux computer, and are extremely useful in robotics, the Blue’s target use.

Right now, the BeagleBone Blue isn’t available, although we do know you’ll be able to buy one this summer. Information on pricing and availability – as well as a few demos – will come in February.