This guide to open source and developer-friendly hardware for IoT device development ranges from simple MCU-based modules to powerful Linux-based SBCs. An Open Source Perspective on the Internet of Things Part 3: Linux and Open Source Hardware for IoT Most of the 21 open source software projects for IoT that we examined […]
There’s hardly a day that passes without an Arduino project that spurs the usual salvo of comments. Half the commenters will complain that the project didn’t need an Arduino. The other half will insist that the project would be better served with a much larger computer ranging from an ARM CPU to a Cray.
[Will Moore] has been interested in BEAM robotics — robots with analog hardware instead of microcontollers. His latest project is a sophisticated line follower. You’ve probably seen “bang-bang” line followers that just use a photocell to turn the robot one way or the other. [Will’s] uses a hardware PID (proportional integral derivative) controller. You can see a video of the result below.
Looking at how [Will] used simulation to devise a PID with opamps and a PWM generator is illustrative. As you can see from the video, the results are good.
We’ve looked at BEAM before. We’ve even seen mutants that combine traditional BEAM circuitry with microcontrollers. But it’s still nice to see the pure analog version running through its paces every once in a while.
Linaro, 96Boards.org, and SeeedStudio have launched the first 96Boards IoT Edition SBC — a $28 BLE-ready “BLE Carbon” that runs Zephyr on an ST Cortex-M4. Linaro Ltd and its 96Boards.org open hardware standardization group announced the first non-Linux and MCU based 96Boards single board computer, and the first to comply with a new 96Boards IoT […]
The BeagleBone is a very popular single board computer, best applied to real-time applications where you need to blink LEDs really, really fast. Over the years, the BeagleBone has been used for stand-alone CNC controllers, the brains behind very large LED installations, and on rare occasions has been used to drive CRTs. If you just want a small Linux board, get a Pi. If you want to do something interesting with hardware, get a BeagleBone.
The BeagleBone ecosystem has grown a lot in the last year, from the wireless and Grove connector equipped BeagleBone Green, the robotics-focused BeagleBone Blue, the Zoolander-inspired Blue Steel. Now there’s a new BeagleBone, built around a very interesting System on Module introduced earlier this year.
The new board is called the BeagleBone Black Wireless, and it brings to the table all you know and love about the BeagleBone. There’s a 1GHz ARM355x with two 32-bit 200MHz PRUs for the real-time pin toggling. RAM is set at 512MB, with 4GB of eMMC Flash and Debian pre-installed, and a microSD card for larger storage options. The new feature is wireless connectivity: a TI WiFi and Bluetooth module with provisions for 802.11s replaces the old Ethernet connector.
Taken at face value, the new BeagleBone Black Wireless deserves a mention — it’s a BeagleBone with wireless — but isn’t particularly noteworthy. But when you get to the gigantic brick of resin dropped squarely in the middle of the board does the latest device in the BeagleBone family become very, very interesting. The System on Module for this version of the BeagleBone is the BeagleBone On A Chip released a few months ago. The Octavio Systems OSD335x is, quite literally, a BeagleBone on a chip. It’s a BGA with big balls, making it solderable with hand-applied solder paste and a toaster oven reflow conversion. In fact, the BeagleBone Wireless was designed by [Jason Kridner] in Eagle as a 6-layer board. It’s still a bit beyond the standard capabilities of OSHPark, but the design can still be cut down, and shows how this BeagleBone on a Chip can be applied to other Open Hardware projects.
Researchers at Tufts University are experimenting with smart thread sutures that could provide electronic feedback to recovering patients. The paper, entitled “A toolkit of thread-based microfluidics, sensors, and electronics for 3D tissue embedding for medical diagnosis”, is fairly academic, but does describe how threads can work as pH sensors, strain gauges, blood sugar monitors, temperature monitors, and more.
Conductive thread is nothing new but usually thought of as part of a smart garment. In this case, the threads close up wounds and are thus directly in the patient’s body. In many cases, the threads talked to an XBee LilyPad or a Bluetooth Low Energy module so that an ordinary cell phone can collect the data.
Of course, sewing strange conductive thread into your body isn’t something most would try out on their own. Still, some of the thread techniques could be useful in other contexts.
If any of you have ever made a piece of clothing, you’ll know some of the challenges involved. Ensuring a decent and comfortable fit for the wearer, because few real people conform exactly to commercial sizes. It’s as much a matter of style as it is of practicality, because while ill-fitting clothing might be a sartorial fail, it’s hardly serious.
When the piece of clothing is a space suit though, it is a different matter. You are not so much making a piece of clothing as a habitat, and one that will operate in an environment in which a quick change to slip into something more comfortable is not possible. If you get it wrong at best your astronaut will be uncomfortable and at worst their life could be threatened.
In the early 1960s, NASA needed to quantify the effects of clothing such as a space suit on a human body. They could dress an astronaut in a suit, but while he could give them a subjective view of its comfort he could not quantise the forces it exerted on his body. Their solution to this problem was to construct a force gauge, an instrument designed to measure all the forces exerted by the suit as it simulated the full range of human movement. PDAD, the Power Driven Articulated Dummy, was the hydraulically driven humanoid result.
PDAD was designed to be adjustable to simulate a range of heights and sizes of typical American males, with a range of movement and torque capability as close as possible to those of a human within the constraints of the components available at the time. The actuators were hydraulic, and the control system was a fairly straightforward analogue servo system with an operator performing all the motions from a console. This meant that it was difficult for more than four joints to be in action at once, the limitation being the operator’s dexterity.
The PDAD dummy for sale is a little battered and worn, and seems to have lost its left elbow, forearm, and hand. There is no sign of the control console and it’s probably safe to guess that it’s not presented as a working example. However it is a fascinating glimpse into the depth and quality of the huge amount of work that went into the early years of human space flight, and if we are lucky it may find its way into another museum so we have the chance to see it at first hand.
If you wave your hand under the water’s surface, you get a pattern of ripples on the surface shortly thereafter. Now imagine working that backwards: you want to produce particular ripples on the surface, so how do you wiggle around the water molecules underneath?
That’s the project that a crew from the University of Navarre in Spain undertook. Working backwards from the desired surface waves to the excitation underwater is “just” a matter of math and physics. The question is then how to produce the right, incredibly irregular, wavefront. The researchers’ answer was 3D printing.
The idea is that, by creating the desired ripples on the water’s surface, the researchers will be able to move things around. We’ve actually seen this done before in air by [mikeselectricstuff], and a more sophisticated version uses multiple ultrasonic transducers and enables researchers to move tiny objects around in mid-air.
What’s cool about the work done underwater by the Navarre group is that all they’re doing is printing out a 3D surface and wiggling it up and down to make the waves. The resulting surface wave patterns are limited in comparison to the active systems, but the apparatus is so much simpler that it ought to be useful for hackers with 3D printers. Let the era of novelty pond hacking begin!
Resistors are one of the fundamental components used in electronic circuits. They do one thing: resist the flow of electrical current. There is more than one way to skin a cat, and there is more than one way for a resistor to work. In previous articles I talked about fixed value resistors as well as variable resistors.
There is one other major group of variable resistors which I didn’t get into: resistors which change value without human intervention. These change by environmental means: temperature, voltage, light, magnetic fields and physical strain. They’re commonly used for automation and without them our lives would be very different.
As you can probably tell from part of the name, thermal, meaning “of or relating to heat”, these are resistors whose resistance changes with temperature. While that’s true of all resistors, with thermistors the change is larger and desired.
They come in two types:
NTC, or Negative Temperature Coefficient thermistors, where as the temperature increases their resistance decreases, and
PTC, or Positive Temperature Coefficient thermistors, where as the temperature increases their resistance increases.
Many Hackaday readers might be familiar with NTC thermistors in 3D printers where they’re used to measure the temperature of the hot end of the extruder. If your printer has a heated bed it is likely also monitored by an NTC.
And there are many more applications where they’re used for measuring temperature such as in digital thermometers, toasters, coffee makers, freezers, and so on.
But in addition to measuring temperature, NTC thermistors are also used for limiting current. As inrush current limiters they limit any rush of high current when a device is first turned on. Basically when the device is turned on, the thermistor is still relatively cool and so acts as a high resistance, limiting the current. Over time, as more current flows through the thermistor, its temperature increases and so its resistance decreases. That allows more current to flow through it, which is fine since the initial rush of high current is finished by that time.
My only experience with NTC thermistors was to play around with one that was part of an automotive sensor. The sensor was to be screwed into the engine compartment possibly for measuring the coolant or oil temperature. Of course this doesn’t measure the temperature directly. Instead a voltage is applied across it. As the temperature changes, the resistance changes and so does the voltage. The vehicle’s computer then uses a table or formula to map that voltage to a temperature.
I couldn’t find the datasheet for the automotive part and didn’t know the relationship between the thermistor’s temperature and resistance so I put it in a pot of water on the stove. As I slowly brought the water to a boil I measured the water temperature and the thermistor’s resistance, obtaining the chart shown here.
Positive Temperature Coefficient (PTC) thermistors, whose resistance increases as temperature increases, also have their uses.
One example is as a replacement for a fuse. As the current in a circuit increases, the temperature of the thermistor increases due to normal resistive heating. This heat is lost to the surroundings. But if the current is higher than it should be then at some point it will heat up faster than it can lose that heat. At that point the resistance will increase, limiting the current.
With the advent of flat panel displays there are fewer and fewer CRT displays around but some readers will remember that PTC thermistors were used in the display’s degaussing coil circuits. The degaussing coil would need to be energized briefly and turned off gradually. The current through the coil would create the needed magnetic field for degaussing, and the current would also heat up the thermistor. As it did, the thermistor’s resistance would increase in the desired gradual manner, reducing the current through the coil until the circuit shut off.
The name varistor doesn’t help much as the name’s origin comes from “varying resistor”, which is a description of all the parts covered in this article and the others in the series. A varistor’s resistance varies according to the voltage, so maybe remembering that it starts with a ‘V’ helps. In a varistor the higher the voltage, the higher the resistance, and the direction of the current doesn’t matter. It’s also much like a diode in that up to a certain minimum voltage it’s off and then turns on (see the voltage-current graph).
Most applications for varistors are in surge protection, protecting circuits from mains transients, inductive loads and from lightning. They’re usually placed across the circuit to be protected so that should the voltage rise high enough across it, the varistor will conduct and act as a short for the current, instead of the current going through the circuit.
My own experience with varistors comes from my time as a solar contractor. We’d attach lightning arresters to various components of the solar system: two arresters for the inverter, where one set of wires ran outdoors to a generator and another set went out to the loads in the cottage, and one arrester for the charge controller where wires ran out to the solar panels. These are all wire runs where voltage can be induced to damaging levels by nearby lightning.
Each of these lightning arresters contains a Metal Oxide Varistor (MOV). The varistor is connected between the wires and ground. As long as the voltage is low enough then current doesn’t conduct. But when lightning strikes somewhere nearby, the voltage on the wires rises and reaches a point where the varistor conducts to ground (e.g. 385 volts). This prevents the voltage from rising further. As long as the solar component is able to handle that voltage then it’s protected. With some standards, the solar component is designed to handle up to 2300 volts where these wires are connected.
A photoresistor’s resistance decreases as light intensity increases. You may also see it referred to as an LDR (Light Dependent Resistor). Its resistance in the dark can be in the megaohms but with the correct wavelengths and sufficient intensity of light, it can be just a few ohms.
Photoresistors aren’t good for detecting rapid changes in light intensity. In going from complete darkness to light, there can be as much as a 10 millisecond delay before the resistance decreases fully. And when going from light to complete darkness the resistance can take as much as 1 second to increase to the megaohm range. However, there are applications where this delay is desireable such as with audio compression. Here an LED or electroluminescent panel is used to control the resistance of the photoresistor and affect the audio signal gain. Doing so is said to sound smoother by softening the attack and release than doing so without a photoresistor.
Another typical application is for a light sensor to detect if a night light should be turned on.
In my case I made a laser communicator that used an audio signal to modulate the output of a dollar store toy laser. I then shined that now fluctuating laser beam onto a distant photoresistor. The photoresistor was part of a circuit that fed an amplifier and the result was the audio signal transmitted by light and reproduced on the amplifier’s speaker. This violated what I mentioned above about not using them for rapid changes in light intensity, but it worked well enough as a fun experiment.
Magneto Resistive Sensor
The resistance of a magneto resistor can be used to detect the position, orientation and strength of a magnetic field. It uses the magnetoresistance effect. The anisotropic magnetoresistance (AMR) effect, discovered in the 1800s is sensitive to the magnetic field strength and the angle between an electric current and the magnetic field. There are other, more recently discovered effects but most conventional resistors use the AMR effect. Magneto resistive sensors that are built around these resistors are available from Digikey and Mouser among others.
I haven’t used magneto resistive sensors myself but one common application is as wheel speed sensors in automobiles. Others are magnetometry, various sensors for angle, rotation and linear positions, and for detecting vehicles on the road.
There is a lot of interesting potential applications for these sensors. At the 2013 Open Hardware Summit a 1-DOF haptick feedback kit called Hapkit was demonstrated by a group from Stanford. They used a magneto resistive sensor to detect a pendulum’s position. That position is then used by a microcontroller to power a motor to make moving the pendulum by hand feel like you’re moving a spring or click wheel.
A strain gauge is an electrical conductor that changes resistance as it’s stretched or compressed, but without breaking, buckling or otherwise permanently deforming it. To get a large enough effect to make a useful change in resistance, the conductor is usually laid out in a zigzag or serpentine pattern with the long ends oriented in the direction of the expected strain.
The change in resistance is very small and so to aid measurement the strain gauge is incorporated in a Wheatstone bridge. A full article could be written about strain gauges and their use in Wheatstone bridges so here’s just a brief overview.
The Wheatstone bridge consists of two voltage dividers, R1 and R2 being one of them, and R3 and R4 being the other one. The input voltage, called the excitation voltage (VEx), is across the outside of the bridge, and the resulting output voltage (Vo) is taken from the centers of the two voltage dividers.
The voltage output, Vo, can be calculated using the formula shown. If the ratio R1/R2 is equal to the ratio R4/R3 then calculating Vo you’ll find you get 0 volts. But if one of the resistors is replaced with a strain gauge then when it’s strained, Vo will become non-zero. Further formulas can be used to convert this to a value in a unit actually called ‘strain’.
Multiple strain gauges can also be used to further amplify the values and to compensate for temperature.
Strain gauges are found in load cells and pressure sensors, both often incorporated in Wheatstone bridges. The ones in pressure sensors are usually made with silicon, polysilicon, metal film, thick film or bonded foil.