Today, Apple has announced their latest bit of hardware. Following in the tradition of the Raspberry Pi, BeagleBone, and the Intel Edison, Apple have released a single board computer meant for embedded and Internet of Things applications. It’s called the Apple Device, and is sure to be a game changer in the field of low-power, Internet-enabled computing.
First off, some specs. The Apple Device uses Apple’s own A8 chip, the same dual-core 64-bit CPU found in the iPhone 6. This CPU is clocked at 1.1 GHz, and comes equipped with 1GB of LPDDR3 RAM and 4GB of eMMC Flash. I/O includes a Mini DisplayPort capable of driving a 4k display, 802.11ac, Bluetooth, and USB. In a massive break from the Apple zeitgeist of the last decade or so, the Apple Device also includes a forty pin header for expansion, much like the Raspberry Pi, BeagleBone, and Edison.
Although Apple’s first foray into the embedded computing market is a shocker, in retrospect it should come as no surprise; the introduction of HomeKit in iOS 9 laid the groundwork for an Internet of Apple Devices, embedded into toasters, refrigerators, smart homes, and cars. The Apple Device lives up to all these expectations, but what is the hands-on experience like?
See our review of the Apple Device after the break.
Micro servomotors are a hacker staple. You’ll find maybe four or five in an RC plane, while a hexbot build could soak up a dozen or more of the cheap and readily available devices. Unfortunately, long-throw linear actuators are a little harder to come by, so it’s nice to know you can 3D-print linear gearing for standard micro RC servos and roll your own.
Currently on revision 2, [Roger Rabbit]’s design is not just a quick and dirty solution. He’s really thought through the problems he observed with his first revision, and the result is a robust, powerful linear actuator. The pinion fits a trimmed servo crank arm, the mating rack is stout and stiff, and early backlash problems have been solved. The whole case is easy to assemble, and as the video below shows, the completed actuator can lift 300 grams.
We like [Roger]’s build process, especially the iterative approach to improving the design. We’ll stay tuned to see where it goes next – a continuous rotation servo for extra-long throws? While we wait, you might want to check out [Richard Baguley]’s recent primer on servos if you want a little background on the underlying mechanism.
We have talked about a whole slew of logic and interconnect technologies including TTL, CMOS and assorted low voltage versions. All of these technologies have in common the fact that they are single-ended, i.e. the signal is measured as a “high” or “low” level above ground.
This is great for simple uses. But when you start talking about speed, distance, or both, the single ended solutions don’t look so good. To step in and carry the torch we have Differential Signalling. This is the “DS” in LVDS, just one of the common standards throughout industry. Let’s take a look at how differential signaling is different from single ended, and what that means for engineers and for users.
Single Ended: TTL, CMOS, LVTTL, Etc.
Single Ended and Sources of Noise
Collectively, standards like TTL, CMOS, and LVTTL are known as Single Ended technologies and they have in common some undesirable attributes, namely that ground noise directly affects the noise margin (the budget for how much noise is tolerable) as well as any induced noise measured to ground directly adds to the overall noise as well.
By making the voltage swing to greater voltages we can make the noise look smaller in proportion but at the expense of speed as it takes more time to make larger voltage swings, especially with the kind of capacitance and inductance we sometimes see.
Enter Differential Signaling where we use two conductor instead of one. A differential transmitter produces an inverted version of the signal and a non-inverted version and we measure the desired signal strictly between the two instead of to ground. Now ground noise doesn’t count (mostly) and noise induced onto both signal lines gets canceled as we only amplify the difference between the two, we do not amplify anything that is in common such as the noise.
The 555 can do anything. OK, that’s become a bit of a trope in our community, but there is quite a lot of truth behind it: this little timer chip is an astonishingly versatile component.
[Alexander Lang] has added another achievement to the 555’s repertoire, he’s used one in the creation of a plasma speaker. Working at Hackspace Manchester, he’s used the 555 as a pulse-width modulator that drives a flyback transformer through a MOSFET, which feeds a spark gap mounted in a lasercut enclosure. The results maybe aren’t yet hi-fi, but it works, and is very audible.
We’ve been following this project for a while, as he’s updated his progress through several iterations. From initial design idea through PCB and enclosure design, to a first working prototype and some audio refinements, and finally this latest post with the spark gap in its enclosure. He is still refining his speaker, so there is more to come
In the video below the break he demonstrates his pulse width modulator, and tests the device using a keyboard as an input.
[Bunnie Huang] recently had the opportunity to do a thorough teardown of the new Formlabs Form 2 printer. It’s a long read, so just head over there and immerse yourself in every detail. If you want the cliff notes, though, read this but still go look at all the pretty pictures.
First, it’s a major upgrade with pretty much every component. The CPU is a huge step up, the interface went from monochrome to full color touch screen, the connectivity has been upgraded with WiFi and Ethernet, the optics are much better and safer, the power supply is integrated, there are lots of little improvements that handle things like bed leveling, calibration, resin stirring, pausing jobs, and resin refilling during a print. Bunnie practically gushes at all the features and impressive engineering that went into the Form 2.
How do you make things move? You add in a motor that converts electrical energy into motion. That’s a simple idea, but how do you know where the motor is? That’s where the servo motor comes in. By adding a sensor and a controller to the mechanism, these motors can figure out how far they have rotated and maintain that setting without any need for external control.
What is a Servo Motor?
These neat devices can be large or small, but they all share the same basic characteristics: a motor connected to a gearing mechanism and an encoder that detects the movement and speed of the motor. This combination means that the controlling device doesn’t need to know anything about the motor itself: the controller on the servo motor handles the process of feeding the appropriate power to the motor until it reaches the requested position. This makes it much easier to build things with servomotors, as the designer has already done all the hard work for you.
The first place that most people encounter a servo motor is in the small hobby servos that are used in remote control vehicles. Manufactured by companies like Hitec and Futaba, these drive a gear or arm that transfers the rotation of the motor to perform tasks like turning a wheel to steer a car, moving a control surface on an RC plane, or any task that requires a small range of motion at high precision. The gearing in the servomotor offers more torque than connecting the shaft directly to the motor. Most hobby servos of this type are restricted to a certain range of motion (usually 180 degrees) because the position encoder is a simple potentiometer connected to the output shaft.
Servomotors usually have three connection wires: a power line, a ground line and a signal line. The signal line is fed a pulse width modulation (PWM) signal that determines the angle that the servomotor moves to. As the name suggests, the length of the pulse (or the width, if you look at it on an oscilloscope) is the thing that controls the angle that the servo moves to: a short pulse (1 millisecond) sets it to the zero angle, while a long pulse of 2 milliseconds sets it to the maximum angle. A pulse length between these two limits signals the servomotor to move to the corresponding angle: 1.5 ms would set it to 90 degrees.
It is important to note that servomotors and stepper motors are not the same thing. Both are used for positioning, but steppers usually run without feedback. Instead, steppers turn (as the name suggest) in discrete steps. To figure out where a stepper motor is requires a limit switch, then driving the stepper until this is triggered. Then if you keep count out the number of steps that it’s traveled, you know where it is. That’s why devices like inkjet or 3D printers will move to their limits when they start up, so the controller can detect the far limit of the mechanism being driven, and calculate the current position from that.
How Do You Use A Servomotor?
Because the designers of servomotors have done most of the hard work for you, servomotors are very easy to use. To drive them, you just need to feed them power (usually 5V) and feed the PWM signal to the servomotor. You can drive them directly from an Arduino or similar microcontroller using a library that converts an angle into a PWM signal on one of the output pins.
Each servomotor requires a dedicated output pin if they are being driven this way, though, so if you are driving a lot of servomotors, a dedicated controller makes more sense. Devices such as the Adafruit Servo Shield and the Pololu Maestro allow you to control multiple servos from a single output pin on the microcontroller: the microcontroller sends a signal to the device addressing each servo in turn, and the device converts this into the PWM signals for each. If you need to drive a lot of servos, the SD84 can control up to 84 servos at once from a single USB port.
In the first article about measurement systems we looked at sensors as a way to bring data into a measurement system. I explained that a sensor measures physical quantities which are turned into a voltage with a variable conversion element such as a resistor bridge. There will always be noise in any system, and an operational amplifier (op-amp) can be used to remove some of that noise. The example we considered used an op-amp in a differential configuration that removes any disturbance signal that is common to both inputs of the op-amp.
But that single application of an op-amp is just skimming the surface of the process of bringing a real-world measurement of a physical quantity into a digital system. Often, you’ll need to do more work on the signal before it’s ready for sampling with a digital-to-analog converter. Signal conditioning with amplifiers is a deep and rich topic, so let me make it clear that that this article will not cover every aspect of designing and implementing a measurement system. Instead, I’m aiming to get you started without getting too technical and math-y. Let’s just relax and ponder amplifiers without getting lost in detail. Doesn’t that sound nice?