Transferring data without error when there is a lot of background noise is a challenge. Dr. Claude E. Shannon in 1948 provided guidance with his theory addressing the capacity of a communications channel in the presence of noise. His work quickly spread beyond communications into other fields. Even other aspects of computer use were impacted. An example is the transfer of data from a storage medium, like a hard drive or CD-ROM. These media and their sensors are not 100% reliable so errors occur. Just as Shannon’s work defines communication channel capacity it defines the transfer rate from a media surface to the read head.
Shannon told us how much could be passed through a channel but didn’t say how. Since 1948 a lot of research effort went into accurately detecting errors and correcting them. Error correction codes (ECC) add extra bits to messages, but their cost pays off in their ability to work around errors. For instance, without ECC the two Voyager spacecraft, now leaving our solar system, would be unable to phone home with the information they’ve gathered because noise would overwhelm their signals. Typically in hardware, like memory, error correction is referred to as ECC. In communications, the term forward error correction (FEC) is used.
Robust communication, or data transfer, is a combination of fancy software and tricky signal processing. I’m going to focus on the software side in this article. You may find some of these techniques useful in communicating data among your devices. While I’ll be using the term communications keep in mind this is applicable to transferring data in general.
Continue reading “Error Detection And Correction: Reed-Solomon, Convolution And Trellis Diagrams”
New York is coming on strong as a hardware epicenter — exciting hardware culture can be found at every turn. Tomorrow, we’re bringing food and fun to one such event, the monthly MakeIt NYC meetup.
MakeIt is hosted by PCB.ng, a Brooklyn based PCB manufacturer and board stuffer whose mission it is to make electronics manufacturing available to everyone. [Sophi Kravitz] will be on hand and speaking about Hackaday.io and the Hackaday Prize. There are many other talks lined up, including The LED Artist (amazing work if you haven’t seen), Microchip who will show off their new Chip-KIT Wi-Fire, Thimble (an electronics subscription service delivering monthly hardware kits), and Botfactory’s Squink, a desktop electronics manufacturing machine.
In addition to the planned talks we’re always interested in seeing the projects you’re working on. Bring along anything that fits in a pocket or a backpack. We’ll see you there!
Late last year, the FAA expanded a Special Flight Rule Area (SFRA) that applied to Unmanned Aerial Systems, drones, and RC airplanes around Washington DC. This SFRA was created around the year 2000 – for obvious reasons – and applies to more than just quadcopters and airplanes made out of foam. Last December, the FAA expanded the SFRA from 15 nautical around a point located at Reagan National to 30 nautical miles. No remote-controlled aircraft could fly in this SFRA, effectively banning quadcopters and drones for six million people.
Today, the FAA has rescinded that ban bringing the area covered under the Washington DC SFRA to 15 nautical miles around a point inside Reagan National. This area includes The District of Columbia, Bethesda, College Park, Alexandria, and basically everything inside the beltway, plus a mile or two beyond. Things are now back to the way they were are few weeks ago.
The 30-mile SFRA included a number of model flying clubs that were shuttered because of the ban. DCRC is now back up. The Capital Area Soaring Association worked with the FAA and AMA to allow club members to fly.
Of course, limitations on remote-controlled aircraft still exist. For the most part, these are rather standard restrictions: aircraft must weigh less than 55 pounds, fly below 400 feet line of sight, and must avoid other aircraft.
We’re not sure that [Alec]’s dad actually requested remote-controlled eyebrows for his birthday, but it looks like it’s what he got! As [Alec] points out, his father does have very expressive eyebrows, and who knows, he could be tired of raising and lowering them by himself. So maybe this is a good thing? But to us, it still looks a tiny bit Clockwork Orange. But we’re not here to pass judgement or discuss matters of free will. On to the project. (And the video, below the break.)
An ATmega328 (
otherwise known as cheap Cloneduino Alec wrote that the 328 was from a real Arduino) is trained to run motors in response to IR signals. An L293D and a couple of gear motors take care of the rest. Sewing bobbins and thread connect the motors to the eyebrows. And while it’s not entirely visible in the photo, and veers back into not-sure-we’d-do-this-at-home, a toothpick serves as an anchor for the thread and tape, secured just underneath the ‘brows for maximum traction.
We have to say, we initially thought it was going to be a high-voltage muscle-control hack, and we were relieved that it wasn’t.
Continue reading “Remote-Controlled Eyebrows For Your Birthday”