Few people would deny that farming is hard work. It always has been, and it probably always will be no matter how fancy the equipment gets. In 1932, farming was especially grueling. There was widespread drought throughout the United States, which gave rise to dust bowl conditions. As if those two things weren’t bad enough, the average income of the American farmer fell to its lowest point during the Depression, thanks to the Smoot-Hawley Tariff Act.
Even so, crop farming was still a viable and somewhat popular career path in 1932. After all, knowing how to grow food is always going to get you elected into your local post-apocalyptic council pretty quickly. As such, the John Deere Equipment Company released the 19th edition of their classic book, The Operation, Care, and Repair of Farm Machinery. This book covers all of the various equipment a crop farmer needed to get from plough to bounty. The text gives equal consideration to horse-driven and tractor-driven farming implements, and there’s an entire chapter dedicated to tractor engine maintenance.
According to its preface, this book was used as an agricultural text in schools and work-study programs. It offers a full course in maintaining the all the (John Deere) equipment needed to work the soil, plant crops, cultivate, harvest, and manure in all parts of the country. The Operation, Care, and Repair of Farm Machinery was so well-received that John Deere kept the book in publication for over thirty years. The 28th edition and final edition came out in 1957. We wonder why they would have stopped putting it out after all that time. Maybe it wasn’t profitable enough, or the company decided to phase out the shade tree tractor mechanic.
So why should you delve into a sorely outdated textbook about farm equipment? Well, it’s straightforwardly written and easy to learn from, whether you’re trying or not. You should check it out if you’re even remotely curious about the basics of farming. If for no other reason, you should go for the beautiful hand-drawn illustrations and stay for the interesting tables and charts in the back. Did you know that a gallon of milk weighs 8.6 pounds?
The biggest hurdle to great advances in wearable technology is the human body itself. For starters, there isn’t a single straight line on the thing. Add in all the flexing and sweating, and you have a pretty difficult platform for innovation. Well, times are changing for wearables. While there is no stock answer, there are some answers in soup stock.
A group of scientists at Stanford University’s Bao Lab have created a whisper thin co-polymer with great conductivity. That’s right, they put two different kinds of insulators together and created a conductor. The only trouble was that the resulting material was quite rigid. With the help of some fancy x-ray equipment, they discovered that adding a molecule found in standard industrial soup thickeners stops the crystallization process of the polymers, leaving them flexible and stretchy. Get this: the material conducts even better when stretched.
The scientists have used the material to make both simple, transparent electrodes as well as entire flexible transistor arrays with an inkjet printer. They hope to influence next generation wearable technology for everything from smart clothing to medical devices. Who knows, maybe they can team up with the University of Rochester and create a conducting co-polymer that can also shape-shift. Check out a brief demonstration after the break.
[Johan] has slipped down the rabbit hole of making musical instruments. His poison? Laser harp MIDI controllers. Having never made one before, he thought he would start small and then iterate using what he learned. Fortunately for us, [Johan] documented the process over on .io, essentially creating a step-by-step guide for building a simple but powerful 16-note laser harp.
Laser Harp I is built around a Teensy 3.2 and, of course, lasers pointed at LDRs. [Johan] used fairly low-power laser modules, which are slightly less blinding if you accidentally look at them for a second, but should still be taken seriously. He added four potentiometers to control the sensitivity, scale, octave, and the transposition. The sensitivity pot essentially accounts for the ambient light in the room. Although it only has 16 notes, Laser Harp I is ready to rock with over 30 different scales to choose from. Check out the brief demo that [Johan] put up on his Instagram.
Today on Hackaday Dictionary, we’re going to talk about the two basic types of control systems: open-loop and closed-loop. We’ll describe the differences between them and explore the various advantages and disadvantages of each. And finally, we’ll talk about what happens when you try to draw a line between the two.
Control systems are literally all around us. They’re illuminating our rooms, laundering our unmentionables, and conspiring to make us late for work. Most of us probably use or interact with at least five control systems before we’re even out the door in the morning. Odds are you’re using a control system to read this article.
When we say ‘control system’, we’re speaking broadly. A control system is defined as any system that exhibits control over a function. It doesn’t matter how big or small the function is. A standard light switch is a simple type of control system. Flip it back and forth and the light is either on or off with no in between. Too bright? Too bad. There is no way to account for light intensity preference, use duration, energy output, or anything else.
Another common example in discussing control system theory is the clothing dryer. Set the timer on the dryer and it will run until time expires. Will it run long enough to dry everything without shrinking anything? The only way to know is to open the door and check.
Both the light switch and the clothes dryer are open-loop systems. The process is a straight line from start to finish, and they operate without concern for their output. Once the light switch is flipped to the on position, current will flow until the switch is reversed. The switch doesn’t know if the bulb is burned out or even screwed into the socket to begin with. And the clothes dryer doesn’t care if your clothes are damp or dry or totally shrunken when time runs out.
Stay in the Loop
In a closed-loop system, the process begins the same way it does in an open-loop system. But a closed-loop system has one or more feedback loops in place that can adjust the process. Sometimes the feedback will simply cause the process to repeat until the desired result is achieved.
Both of our open-loop control system examples above could easily be converted to closed-loop systems. A more advanced light switch might take input from a photo cell, or it could poll a motion detector and turn the lights off after a period of no detectable activity in the room. The clothes dryer could be improved with the addition of a moisture sensor. Since the humidity level in the dryer will change during the cycle, why not poll a DHT22 and re-run the process until a predetermined humidity level is reached? Then the dryer becomes a closed-loop system. No more reaching in and fondling the towels and shirt collars to make sure everything is dry. Well, at least in theory.
Some control systems exist in both forms. Traffic lights are a good example of this phenomenon. Some lights are open-loop and simply run on a schedule. Many more of them are closed-loop and will cycle differently depending on traffic flow or information received from other traffic lights. The really smart ones have Emergency Vehicle Preemption (EVP) receivers. This is the system that allows fire trucks and some other emergency vehicles to change the lights in their favor. A device in the vehicle strobes a specific pattern at the receiver module on the light post, and the light changes as soon as possible.
Advantages and Disadvantages
The main advantage of closed-loop systems is fairly obvious: using feedback means more and better control. But there are trade-offs. It’s almost impossible to deal with all the what-ifs in creating any system, and this generates unforeseen issues. They aren’t all bad, though. Maybe you’re sitting peacefully in the corner engrossed in a book, and the motion detector-driven lights shut off because you aren’t moving around enough. That isn’t ideal, but it’s easy enough to turn the lights back on and keep reading.
The unforeseen issues can be so much worse than sudden darkness. Case in point: robotic vacuum cleaners. Here you have a complexly closed-loop system to take care of one of life’s drudgeries. Should be awesome, right? Yes, but because it is blind to everything but its pre-programmed boundaries, it doesn’t know not to spread messes around.
A lot of closed-loop control systems look great on paper, but their imperfections become clear in execution. Take cruise control for example. Here is a system that’s better at its job than humans are. It will maintain the set speed until you hit the brakes or run out of gas. It will perform as intended whether there is a headwind or a tailwind or you’re towing a boat or transporting rowdy children. But cruise control isn’t aware of cliffs or guard rails or deer darting out in front of the car. Cruise control keeps its head down and does its job until it can’t go on.
Open-loop systems may not be as smart as closed-loop systems, but they often shine in their simplicity. For the most part, they do what you expect them to do. Light goes on, light goes off. And they are arguably more dependable since there are fewer things that can go wrong. Of course, a “simple” open-loop control system can mean a steeper learning curve. It’s not easy to learn to drive a manual transmission. But if you don’t know how to drive one, you’re missing out on some nice advantages, like the ability to push start the thing if you have to, and the option to downshift instead of pumping the brakes in icy conditions. So the question is this: is an open-loop system more valuable than a closed-loop system if it means having more control over the process? Does it depend entirely on the process in question?
Open-Loop vs. Closed-Loop
So where exactly does open-loop end and closed-loop begin? The line seems clear for some systems, but muddy for others. How much feedback is enough to qualify? Add just about anything to a light switch and it seems safe to say that you took it from open- to closed-loop.
More often than not, the line between the two is blurry. Think of a motorized garage door. You push the button and the door either opens or closes. Push it again and the door moves in the opposite direction. Most modern garage doors have a fail-safe in place to stop the garage door in the event of an emergency. If the door encounters any resistance, it will stop and reverse direction.
The break beam detector is supposed to keep people and their tricycles from being crushed if they happen to be in the way while the door is closing. But it only works if the person or thing breaks the IR beam. There’s only one beam, and it sits about six inches off the floor. The motorized garage door system is actually quite limited because it has no positional awareness. It doesn’t know where it is on the track, it’s just going up and down blindly, waiting for input or resistance.
Not all doors can be counted on to stop if they feel resistance—I tested mine and it kept on going. So if I don’t pull far enough into the garage and then put the door back down, it might hit the protruding rear end of my hatchback. It’s in the way of the door closing, but it sits way too high to break the beam. So is the garage door really, truly a closed-loop system?
Finally, there’s a way to get rid of those applicator-less tampons that literally no one uses while also destroying a bunch of Axe body spray. Just use the Axe as the propellant in a 3D-printed, gas-powered tampon gun.
As you’ll see in the assembly and demonstration video after the break, most of the parts in [HarambesLabs]’ modular gun design are 3D-printed. Aside from those, you just need to add a PVC tube for a barrel, a bottle that fits the threading on the body, and a pair of o-rings to make a nice, tight seal. Snap in the piezo mechanism from a lighter, fill the bottle with an Axe cloud, and screw it on to the body. If the gas/air mixture is close enough, the compacted cotton bullet should fly. The gun is single-shot, but [HarambesLabs] is working on a mod to make it fully automatic.
We love a good gun build around here, be it mostly benign or downright terrifying. This build isn’t necessarily tampon-dependent but the size, weight, and plastic covering (reducing friction) make it ideal for this particular design. Nerf darts may be another option if you can find the correct fit for the barrel.
The camera, in this case the one from an iPhone 6, is mounted to an off-the-shelf robot chassis that tools around on a pair of DC motors. The camera mount uses a stepper motor to get just the right shot. A PIC32 on board the ‘bot takes Bluetooth commands from an iOS app that the team built. The dolly works two ways: it can be controlled manually in free mode, or it can follow a predetermined path at a set speed for a specified time in programmed mode.
Our favorite part of the build? The camera’s view is fed to a smart watch where [Ope] and his team can take still pictures using the watch-side interface. Check it out after the break, and stick around for a short time-lapse demo. We’ve featured a couple of dolly builds over the years. Here’s a more traditional dolly that rides a pair of malleable tubes.
On paper, bicycling is an excellent form of transportation. Not only are there some obvious health benefits, the impact on the environment is much less than anything not directly powered by a human. But let’s face it: riding a bike can be quite scary in practice, especially along the same roads as cars and trucks. It’s hard to analyze the possible threats looming behind you without a pair of eyes in the back of your head.
[Claire Chen] and [Mark Zhao] have come up with the next best thing—bike sonar. It’s a two-part system that takes information from an ultrasonic rangefinder and uses it to create sound-localized pings in a rider’s ears. The rangefinder is attached to a servo mounted on the seat post. It sweeps back and forth to detect objects within 4 meters, and this information is displayed radar-sweep-style graphic on a TFT screen via a PIC32.
Though the graphic display looks awesome, it’s slow feedback and a bit dangerous to have to look down all the time — the audio feedback is by far the most useful. The bike-side circuits sends angle and distance data over 2.4GHz to another PIC mounted on a helmet. This PIC uses sound localization to create a ping noise that matches the distance and location of whatever is on your tail. The ping volume is relative to the distance of the object, and you just plug headphones into the audio jack to hear them. Bunny-hop your way past the break to check it out.