If you’ve ever turned a rotary encoder or pushed a cursor button and had it skip a step or two, you’ve suffered directly from button bounce. My old car stereo and my current in-car GPS navigator both have this problem, and it drives me nuts. One button press should be one button press. How hard is that to get right?
In the last session of Embed with Elliot, we looked into exactly how hard it is to get right and concluded that it wasn’t actually all that bad, as long as you’re willing to throw some circuitry at the problem, or accept some sluggishness in software. But engineers cut corners on hardware designs, and parts age and get dirty. Making something as “simple” as a button work with ultra-fast microcontrollers ends up being non-trivial.
And unsurprisingly, for a problem this ubiquitous, there are a myriad of solutions. Some are good, some are bad, and others just have trade-offs. In this installment, we’re going to look at something special: a debouncer that uses minimal resources and is reasonably straightforward in its operation, yet which can debounce along with the best of ’em.
In short, I’ll introduce you to what I think is The Ultimate Debouncer(tm)! And if you don’t agree by the end of this article, I’ll give you your money back.
If you read Hackaday regularly, you’ve probably heard that you can use a LASER to create graphene. There’s been a bit of research on how to make practical graphene supercapacitors using the technique (known as LIG or LASER-induced graphene). Researchers at Rice University have been working on this, and apparently they’ve had significant success inducing graphene capacitors on a Kapton substrate. The team has published a paper in Advanced Materials (which is behind a paywall) about their work.
In particular, Rice claims that they have easily produced supercapacitors with an energy density of 3.2 mW/cubic centimeter (that’s what the University’s website reports; they probably mean mW-hours/cubic centimeter) with capacitances near one millifarad per square centimeter. A key benefit of the construction method is that the capacitors continued to work after researchers bent them 10,000 times. A flexible capacitor is useful in wearable devices that would often flex, or in a device like a cell phone that could bend in your back pocket as you sit.
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!
The minuscule size of the Raspberry Pi Zero makes it perfect for hacks where size is a factor. For example, a small, standalone device for getting streaming audio into your speakers. The RPi Zero doesn’t have an audio output on board, so PolyVection paired it up with their PlainDAC to build a minimal audio streaming device.
Their build uses a few lines from the GPIO header to drive an I2S digital to analog converter. The DAC is a PCM5142 from Texas Instruments that provides high quality sound output, and contains a built in programmable DSP.
The hardware fits into a 3D printed case, coming in at 68 mm by 48 mm. There’s no WiFi inside, but this can be added with an external USB device for wireless streaming. The DAC used is supported by the Linux kernel, so a simple configuration is all that’s needed to pipe audio out.
Once you have a device like this assembled, you can install a server like Music Player Daemon to remotely control the device and cue up internet radio channels.
Where you might see a can, [Adam Kumpf] sees a robot. [Adam’s] robot (named [Canny]) doesn’t move around, but it does have expressive eyebrows, multicolored eyes, and a speaker for a mouth. What makes it interesting, though, is the fact that it receives audio commands via the headphones it wears. You can see [Canny] in action in the video below.
The headphones couple audio tones to [Canny’s] microphone using AFSK (audio frequency shift keying). [Canny] uses an opamp to bring the microphone level up and then uses a 567 PLL IC to decode the audio tones. [Adam] selected two clever frequencies for the mark and space (12345 Hz and 9876 Hz). In addition to being numerically entertaining, the frequencies are far enough apart to be easy to detect, pass through the headphones with no problem, and are not harmonically related.
French robot-artist [Lyes Hammadouche] tipped us off to one of his latest works: a collaboration with [Ianis Lallemand] called Texel. A “texel” is apparently a time-pixel, and the piece consists of eight servo-controlled hourglasses that can tip themselves over in response to viewers walking in front of them. Besides making graceful wavelike patterns when people walk by, they also roughly record the amount of time that people have spent looking at the piece — the hourglasses sit straight up when nobody’s around, resulting in a discrete spatial representation of people’s attentions to the piece: texels.
We get jealous when we see artists playing around with toys like these. Texel uses LIDAR scanners, Kalman-filtered naturally, to track the viewers. openFrameworks, OpenCV, and ROS. In short, everything you’d need to build a complex, human-interactive piece like this using completely open-source tools from beginning to end. Respect!
There’s just something so satisfying about industrial design from the years past. [Kenneth] found an old “portable” tube TV and decided to give it a little upgrade so he could keep it around the house.
It was a black and white Singer TV, with a whopping 6″ tube display. Using his trusty screwdriver set he took the whole thing apart, keeping only the frame and outer casing. Inside he jammed a 5″ LCD display, a Raspberry Pi and a power supply — with some room to spare. He also replaced the speakers with some upgraded baby woofers and an audio amp for the Pi.
The end result is a pretty snazzy little device capable of playing movies, games, or hypothetically, even as an all-in-one computer — but who actually uses a Raspberry Pi as their daily driver? Especially one with only a 5″ display…
But it’s a cutie, and sits nicely on the coffee table. For a larger retro TV rework, we’re quite partial to this conversion of a Philco TV (a sub-brand of Phillips) with a flat panel LCD.
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 
