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4965 Articles

Error Detection And Correction: Reed-Solomon, Convolution And Trellis Diagrams

February 10, 2016 by 32 Comments

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.

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Experiments With A Bowden Extruder Filament Force Sensor

February 9, 2016 by 20 Comments

We were excited to learn that someone had started working with force sensors on filament extruders, especially after we posted about a recent development in filament thickness sensors.

[airtripper] primarily uses a Bowden extruder, and wanted to be a little more scientific in his 3D printing efforts. So he purchased a force sensor off eBay and modified his extruder design to fit it. Once installed he could see exactly how different temperatures, retraction rates, speed, etc. resulted in different forces on the extruder. He used this information to tune his printer just a bit better.

More interesting, [airtripper] used his new sensor to validate the powers of various extruder gears. These are the gears that actually transfer the driving force of the stepper to the filament itself. He tested some of the common drive gears, and proved that the Mk8 gear slipped the least and provided the most constant force. We love to see this kind of science in the 3D printing community — let’s see if someone can replicate his findings.

 

Learn Resin Casting Techniques: Duplicating Plastic Parts

February 9, 2016 by 40 Comments

Resin casting lets you produce parts that would be otherwise impossible to make without a full CNC and injection molding set-up. It costs about as much as a 3d printer, 300 to 600 US dollars, to get a good set-up going. This is for raw material, resin, dye, pressure chamber, and an optional vacuum degassing set-up. A good resin casting set-up will let you produce parts which are stronger than injection molding, and with phenomenal accuracy, temperature resistance, and strength. I will be covering various techniques from the simple to advanced for using resin casting from a hacker’s perspective.

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This Car Lets You Fistbump To Unlock

February 9, 2016 by 14 Comments

In the dark ages, you had to use a key to lock and unlock your car doors. Just about every car now has a remote control on the key that lets you unlock or lock with the push of a button. But many modern cars don’t even need that. They sense the key on your person and usually use a button to do the lock or unlock function. That button does nothing if the key isn’t nearby.

[Pierre Charlier] wanted that easy locking and unlocking, so he refitted his car with a Keyduino to allow entry with an NFC ring. What results is a very cool fistbump which convinces your car to unlock the door.

Keyduinio is [Pierre’s] NFC-enabled project, but you can also use a more conventional Arduino with an NFC and relay shield. The demo also works with a smartphone if you’re not one for wearing an NFC ring. Going this round, he even shows how to make it work with Bluetooth Low Energy (BLE).

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Local Hacker Discovers Card Edge Connectors

February 8, 2016 by 56 Comments

When [turingbirds] was looking around for the absolute minimum connector for a JTAG adapter, he wanted something small, that didn’t require expensive adapters, and that could easily and reliably connect a few JTAG pins to a programmer. This, unsurprisingly, is a problem that’s been solved many times over, but that doesn’t mean there isn’t room for improvement. [turingbirds] found his better solution by looking at some old card edge connectors.

Instead of 0.1″ pitch pin headers, weirder and more expensive connectors, the Tag Connect, or even pogo pins, [turingbirds] came up with a JTAG adapter that required no additional parts, had a small footprint, and could be constructed out of trash usually found behind any busy hackerspace or garage. The connector is based on the venerable PCI connector, chopped up with a Dremel and soldered to a JTAG or ISP programmer.

This is simply a card edge connector, something the younglings seem to have forgotten. Back in the day, card edge connectors were a great way to connect peripherals, ports, and anything else to the outside world. They were keyed, and you could only put them in one way. They were relatively cheap, and with a big coil of ribbon cable, you could make custom adapters easily. For low-speed connections that will only be used a few times, it’s very hard to beat a card edge connector.

Of course the connector itself is only half of the actual build. To turn a chopped up PCI connector into a JTAG adapter, [turingbirds] made footprint and part files for his favorite PCB design tool. In this case it’s Eagle, and the libraries that will plop one of these connectors down are available on GitHub.

Is this the latest and greatest way to plug a programmer into a board? No, because this has been around for 30 or 40 years. It does, however, put a programming port on a PCB with zero dollars in components, a minimum of board footprint, and uses parts that can be salvaged from any pile of old computers.

The Coming Age Of 3D Integrated Circuits

February 8, 2016 by 60 Comments

The pedagogical model of the integrated circuit goes something like this: take a silicone wafer, etch out a few wells, dope some of the silicon with phosphorous, mask some of the chip off, dope some more silicon with boron, and lay down some metal in between everything. That’s an extraordinarily basic model of how the modern semiconductor plant works, but it’s not terribly inaccurate. The conclusion anyone would make after learning this is that chips are inherently three-dimensional devices. But the layers are exceedingly small, and the overall thickness of the active layers of a chip are thinner than a human hair. A bit of study and thought and you’ll realize the structure of an integrated circuit really isn’t in three dimensions.

Recently, rumors and educated guesses coming from silicon insiders have pointed towards true three-dimensional chips as the future of the industry. These chips aren’t a few layers thick like the example above. Instead of just a few dozen layers, 100 or more layers of transistors will be crammed into a single piece of silicon. The reasons for this transition range from shortening the distance signals must travel, reducing resistance (and therefore heat), and optimizing performance and power in a single design.

The ideas that are influencing the current generation of three-dimensional chips aren’t new; these concepts have been around since the beginnings of the semiconductor industry. What is new is how these devices will eventually make it to market, the challenges currently being faced at Intel and other semiconductor companies, and what it will mean for a generation of chips several years down the road.

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Greased Lightning Shows 360 Degrees

February 7, 2016 by 41 Comments

A lot of people got drones for Christmas this year (and many Hackaday readers already had one, anyway). A lot of these drones have cameras on them. The expensive ones beam back live video via RF. The cheaper ones just record to an SD card that you can download later.

If you are NASA, of course, this just isn’t good enough. At the Langley Research Center in Virginia, they’ve been building the Greased Lightning (also known as the GL-10) which is a 10-engine tilt-prop unmanned aerial vehicle. The carbon fiber drone is impressive, sure, but what wows is the recent video NASA released (see below).

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