There is surprising variation in the performance of SD cards. They are not all created equal and the differences can impact the running of your Raspberry Pi, no matter which model. [Jeff Geerling] wondered exactly how different cards would affect system performance. He ran a number of tests on cards ranging from cheap no-names to well-known brand names. The no-name cards fared pretty badly but even among the brand names there is considerable variation.
[Matt] over at Raspberry Pi Spy also tested SD cards and found similar differences. Both tested microSD cards. [Jeff’s] tests were solely on the Pi while [Matt’s] were on Windows 7, Ubuntu, and a Pi.
The discussions in the blog about what to measure were as interesting as the actual results. That lead to determining which software tools to use for the measurement. For example, a system doing a lot of small database reads and writes might work better with one SD card while a system storing and then streaming videos might work better with another card. Another interesting result is that the Pi’s data bus greatly limits the access speeds. [Jeff] measured much higher speeds running the same tests using a Mac with a USB dongle. The cards are capable of much more than the Pi can deliver.
[Matt] also checked the capacity of the SD cards. There are a lot of fakes floating around marked with higher capacities than they actually support. Even getting a brand name card may not help since some are counterfeit. So beware: if the price it too good to be true, it very well may be.
Motors are everywhere; DC motors, AC motors, steppers, and a host of others. In this article, I’m going to look beyond these common devices and search out more esoteric and unusual electronic actuators that might just find a place in one of your projects. In any case, their mechanisms are interesting in their own right! Join me after the break for a survey of piezo, magnetostrictive, magnetorheological, voice coils, galvonometers, and other devices. I’d love to hear about your favorite actuators and motors too, so please comment below!
Piezoelectric materials sometimes seem magic. Apply a voltage to a piezoelectric material and it will move, as simple as that. The catch of course is that it doesn’t move very much. The piezoelectric device you’re probably most familiar with is the humble buzzer. You’d usually drive these with less than 10 volts. While a buzzer will produce a clearly audible sound you can’t really see it flexing (as it does shown above).
To gauge the motion of a buzzer I recently attempted to drive one with a 150 volt piezo driver, this resulted in a total deflection of around 0.1mm. Not very much by normal standards!
The PiezoMotor LEGS actuator “walks” along a rod, pushing it as it goes.
For some applications however resolution is of primary interest rather than range of travel. It is here that piezo actuators really shine. The poster-boy application of piezo actuators is perhaps the scanning probe microscope. These often require sub-nanometer accuracy (less than 1000th of 1000th of 1 millimeter) in order to visualize individual atoms. Piezo stacks are ideal here (though hackers have also used cheap buzzers!).
Sometimes though you need high precision over a larger range of travel. There are a number of piezo configurations that allow this. Notably Inchworm, “LEGS”, and slip-stick actuators.
The PiezoMotor LEGS actuator is shown to the above. As noted, Piezos only produce small (generally sub-millimeter) motion. Rather than using this motion directly, LEGS uses this motion to “walk” along a rod, pushing it back and forth. The rod is therefore moved, in tiny nanometer steps. However, piezos can move quickly (flexing thousands of times a second). And the LEGS (and similar Inchworm actuator) allows relatively quick, high force, and high resolution motion.
The tablecloth trick (yes this one’s fake, the kid is ok don’t worry. :))
Another type of long travel piezo actuator uses the “stick-slip phenomenon”. This is much like the tablecloth magic trick shown above. If you pull the cloth slowly there will be significant friction between the cloth and this crockery and they will be dragged along with the cloth. Pull it quickly and there will be less friction and the crockery will remain in place.
This difference between static and dynamic friction is exploited in stick-slip actuators. The basic mechanism is shown in the figure below.
Motion caused by a stick-slip motor
When extending slowing a jaw rotates a screw, but if the piezo stack is compressed quickly the screw will not return. The screw can therefore be made to rotate. By inverting the process (extending quickly, then compressing slowly) the process is reversed and the screw is turned in the opposite direction. The neat thing about this configuration is that it retains much of the piezo’s original precision. Picomotors have resolutions of around 30 nanometer over a huge range of travel, typically 25mm, they’re typically used for optical focusing and alignment and can be picked up on eBay for 100 dollars or so. Oh and they can also be used to make music. Favorites include Stairway to Heaven, and not 1 but 2 versions of Still Alive (from Portal). Obligatory Imperial March demonstration is embedded here:
There are numerous other piezo configurations, but typically they are used to provide high force, high precision motion. I document a few more over on my blog.
Magnetostrictive actuators
Magnetostriction is the tendency of a material to change shape under a magnetic field. We’ve been talking about magnetostriction quite a lot lately. However much like piezos it can also be used for high precision motion. Unlike piezos they require relatively low voltages for operation and have found niche applications.
Magnetorheological motion
Magnetorheological (MR) fluids are pretty awesome! Much like ferrofluids, MR fluids respond to changes in magnetic field strength. However, unlike ferrofluids it’s their viscosity that changes.
This novel characteristic has found applications in a number of areas. In particularly the finishing of precise mirrors and lens used in semiconductor and astronomical applications. This method uses an electromagnet to change the viscosity of the slurry used to polish mirrors, removing imperfections. The Hubble telescope’s highly accurate mirrors were apparently finished using this technique (though hopefully not that mirror). You can purchase MR fluid in small quantities for a few hundred dollars.
Electrostatic motors
While magnetic motors operate through the attraction and repulsion of magnetic fields, electrostatic motors exploit the attraction and repulsion of electric change to produce motion. Electrostatic forces are orders or magnitude smaller that magnetic ones. However they do have niche applications. One such application is MEMS motors, tiny (often less than 0.01mm) sized nanofabricated motors. At these scales electromagnetic coils would be too large and specific power (power per unit volume) is more important than the magnitude of the overall force.
Voice coils and Galvanometers
The voice coil is your basic electromagnet. They’re commonly used in speakers, where an electromagnet in the cone reacts against a fixed magnet to produce motion. However voice coil like configurations are used for precise motion control elsewhere (for example to focus the lens of an optical drive, or position the read head of a hard disc drive). One of the cooler applications however is the mirror galvanometer. As the name implies the device was originally used to measure small currents. A current through a coil moved a rod to which a mirror was attached. A beam of light reflect off the mirror and on to a wall effectively created a very long pointer, amplifying the signal.
These days ammeters are far more sensitive of course, but the mirror galvanometer has found more entertaining applications:
High speed laser “galvos” are used to position a laser beam producing awesome light shows. Modern systems can position a laser beam at kilohertz speeds, rendering startling images. These systems are effectively high speed vector graphic like line drawing systems, resulting in a number of interesting algorithmic challenges. Marcan’s OpenLase framework provides a host of tools for solving these challenges effectively, and is well worth checking out.
In this article I’ve tried to highlight some interesting and lesser known techniques for creating motion in electronic systems. Most of these have niche scientific, industrial or artistic applications. But I hope they also also offer inspiration as you work on your own hacks! If you have a favorite, lesser known actuator or motor please comment below!
These are the times that we live in: the Raspberry Pi Zero comes out — a full freaking Linux computer on a chip for $5 — and people complain that it doesn’t have this or that. Top place on the list of desiderata is probably a tie between audio out and WiFi connectivity. USB is a solution for both of these, but with one USB port it’s going to be a scarce commodity, so any help is welcome.
Hackaday.io hacker [ajlitt] is looking for a way out of the WiFi bind. His solution? The Raspberry Pi series of chips has a special function on a bunch of the GPIO pins that make it easier to talk to SDIO devices. SDIO is an extension of the SPI-like protocol that’s used with SD memory cards. The idea with SDIO was that you could plug a GPS or something into your PDA’s SD card slot. We don’t have PDAs anymore, but the SDIO spec remains.
[ajlitt] dug up an SDIO driver for the ESP8089 chip, and found that you can liberate the ESP8266’s SPI bus by removing a flash memory chip that’s taking up the SPI lines. Connect the SPI lines on the ESP8266 to the SDIO lines on the Raspberry Pi, and the rest is taken care of by the drivers. “The rest”, by the way, includes bringing the ESP’s processor up, dumping new firmware into it over the SPI/SDIO lines to convince it to act as an SDIO WiFi adapter, and all the rest of the hardware communication stuff that drivers do.
The result is WiFi connectivity without USB, requiring only some reasonably fine-pitch soldering, and unlike this hack you don’t have to worry about USB bus contention. So now you can add a $2 WiFi board to you $5 computer and you’ve still got the USB free. It’s not as fast as a dedicated WiFi dongle, but it gets the job done. Take that, Hackaday’s own [Rud Merriam]!
In 2003, nothing could stop AMD. This was a company that moved from a semiconductor company based around second-sourcing Intel designs in the 1980s to a Fortune 500 company a mere fifteen years later. AMD was on fire, and with almost a 50% market share of desktop CPUs, it was a true challenger to Intel’s throne.
AMD began its corporate history like dozens of other semiconductor companies: second sourcing dozens of other designs from dozens of other companies. The first AMD chip, sold in 1970, was just a four-bit shift register. From there, AMD began producing 1024-bit static RAMs, ever more complex integrated circuits, and in 1974 released the Am9080, a reverse-engineered version of the Intel 8080.
AMD had the beginnings of something great. The company was founded by [Jerry Sanders], electrical engineer at Fairchild Semiconductor. At the time [Sanders] left Fairchild in 1969, [Gordon Moore] and [Robert Noyce], also former Fairchild employees, had formed Intel a year before.
While AMD and Intel shared a common heritage, history bears that only one company would become the king of semiconductors. Twenty years after these companies were founded they would find themselves in a bitter rivalry, and thirty years after their beginnings, they would each see their fortunes change. For a short time, AMD would overtake Intel as the king of CPUs, only to stumble again and again to a market share of ten to twenty percent. It only takes excellent engineering to succeed, but how did AMD fail? The answer is Intel. Through illegal practices and ethically questionable engineering decisions, Intel would succeed to be the current leader of the semiconductor world.
Off-grid living isn’t for everyone, but it has gotten easier in recent years. Cheap solar panels and wind turbines let you generate your own power, and there are plenty of strategies to deal with fuel, water and sanitation. But the one thing many folks find hard to do without – high-speed internet access – has few options for the really remote homestead. [tlankford01] wants to fix that and is working on an open-source mesh network to provide high-speed internet access to off-grid communities.
But first he had to deal with a major problem. With high-speed access provided by a Clearwire wireless network, streaming content to his two flat-screen TVs wasn’t a problem. At least until Sprint bought Clearwire and shut down the service in early November. Another ISP covered his area, but his house lies in a depression out of line of sight of their tower. So he rigged up a bridge between the WiMAX network and his lab. The bridge sits on a hill in sight of the ISP’s tower 3.5 miles away. Solar panels, a charge controller and deep-cycle batteries power everything, and a wireless link down the hill rounds out the build.
This is obviously a temporary solution, and probably wouldn’t last long in winter weather. But it’s working for now, and more importantly it’s acting as proof of concept for a larger mesh system [tlankford01] has in mind. There are plenty of details on what that would look like on his project page (linked above), and it’s worth a look too if you’re interested in off-grid connectivity.
The man leaned over his creation, carefully assembling the tiny pieces. This was the hardest part, placing a thin silver plated diaphragm over the internal chamber. The diaphragm had to be strong enough to support itself, yet flexible enough to be affected by the slightest sound. One false move, and the device would be ruined. To fail meant a return to the road work detail, quite possibly a death sentence. Finally, the job was done. The man leaned back to admire his work.
The man in this semi-fictional vignette was Lev Sergeyevich Termen, better known in the western world as Léon Theremin. You know Theremin for the musical instrument which bears his name. In the spy business though, he is known as the creator of one of the most successful clandestine listening devices ever used against the American government.
PVC is a great building material that can be used for everything from yurts and geodesic domes to pressure vessels. One thing we haven’t seen a lot of is bending PVC pipe. [Lou] wanted to build a Cyr wheel for his daughter, and instead of shelling out five hundred big ones for an aluminum version, he build one out of PVC using techniques usually reserved for woodworking.
A Cyr Wheel is usually a large aluminum hoop built for acrobatic performances. These performances are pretty impressive and look like a lot of fun, but the wheels themselves are rather expensive. Figuring PVC was a good enough solution, [Lou] built his own Cyr wheel for $50 in materials.
The build started off by laying out a jig on the floor. Two sheets of plywood were laid out, a radius for the wheel traced, and a bunch of blocks were glued to the perimeter of this mold. With the mold in place, a few pieces of PVC were flexed into position, clamped, heated with a hair dryer to relieve stress, and glued to a second course of PVC.
The process [Lou] used to build his Cyr wheel isn’t that different from extremely common woodworking techniques. In fact, it wouldn’t be unreasonable for [Lou] to build a wooden Cyr wheel with the same jig. We’re wondering how well this project will stand up to abuse, so if you have any insight to the uses of structural PVC drop a note in the comments.
This novel characteristic has found applications in a number of areas. In particularly the finishing of precise mirrors and lens used in semiconductor and astronomical applications. This method uses an electromagnet to change the viscosity of the slurry used to polish mirrors, removing imperfections. The Hubble telescope’s highly accurate mirrors were apparently finished using this technique (though hopefully not 
