[Billy] has a special interest in passive hydroponics (also known as the Kratky method), which is a way of growing plants in nutrient-rich water that does not circulate. As the plant grows and liquid level drops, only the tips of the roots remain submerged while more and more of the root surface is exposed to oxygen in a harmonious balance. However, “thirsty” plant types (tomatoes, for example) throw off this balance, and the system needs to be modified. To address this, [Billy] designed and printed a passive float valve system that takes care of topping up the reservoir only when needed, without using pumps or any other electrical equipment.
Commercial or industrial float valves are too big to use in his small tanks, which led [Billy] to test dozens of DIY designs. He used everything from plastic water bottles to pipe ends, but nothing quite measured up. With 3D printing, [Billy] was able to create a sealed, lightweight float that exactly matched the housing and tube locations.
The way [Billy]’s float valve works is by using a hollow object as a kind of buoyant plug inside a housing. When the water level is high, the buoyant object rises up and presses a strip of silicone against an outlet, preventing water from flowing. If the water level is low, the buoyant plug drops and water is free to flow. With a reservoir of fresh nutrient-rich water placed above the grow tank, gravity takes care of pushing a fresh supply down a tube, so no active pump is needed. Combined with a passive float valve, the system pretty much runs itself.
Watch [Billy] give a tour of his system and valve design in the video embedded below. He’s got a lot of experience when it comes to working with projects involving liquids. Only someone as comfortable as he is would make his own DIY dishwasher.
Using circuit simulating software like SPICE can be a powerful tool for modeling the behavior of a circuit in the real world. On the other hand, it’s not always necessary to have all of the features of SPICE available all the time, and these programs tend to be quite expensive as well. To that end, [Wes Hileman] noticed an opportunity for a specific, quick method for performing impedance calculations using python without bulky, expensive software and came up with a program which he calls fastZ.
The software works on any network of passive components (resistors, capacitors, and inductors) and the user can specify parallel and series connections using special operators. Not only can the program calculate the combined impedance but it can perform frequency analysis at a specified frequency or graph the frequency response over a wide range of frequencies. It’s also running in python which makes it as simple as importing any other python package, and is also easy to implement in any other python program compared to building a simulation and hoping for the best.
If you find yourself regularly drawing Bode plots or trying to cobble together a circuit simulation to work with your python code, this sort of solution is a great way to save a lot of headache. It is possible to get the a piece of software like SPICE to to work together with other python programs though, often with some pretty interesting results.
Passive homes are a fairly recent trend in home building, but promise a future with minimal energy inputs in our day-to-day. One of the challenges in this year’s Hackaday Prize is to envision ways to add utility to earthen homes often used in refugee camps where there is a housing crisis. Adding passive utilities to these adobe buildings would be a fantastic upgrade, so [Cat] decided to tackle the challenge by creating a refrigerator that needs no electricity.
The the plan for the device works by using evaporative cooling to reduce the temperature in a small box which can be used for food storage. Of course, using evaporative cooling means that you need ready access to water and it likely won’t work in a humid or cool environment, but systems like these have been in use for centuries in plenty of places around the world. [Cat]’s plan is a little more involved than traditional methods of evaporative cooling though, and makes use of a specially painted chimney which provides the airflow when heated by sunlight.
The project is still in its infancy but it would be interesting to see a proof-of-concept built in a real-life passive house in an arid environment. Unfortunately, those of us in humid (or tropical) environments will have to look elsewhere for energy-efficient cooling solutions.
If your neighborhood is anything like ours, walking across the street is like taking your life in your own hands. Drivers are increasingly unconcerned by such trivialities as speed limits or staying under control, and anything goes when they need to connect Point A to Point B in the least amount of time possible. Monitoring traffic with this passive radar will not do a thing to slow drivers down, but it’s a pretty cool hack that will at least yield some insights into traffic patterns.
The principle behind active radar – the kind police use to catch speeders in every neighborhood but yours – is simple: send a microwave signal towards a moving object, measure the frequency shift in the reflected signal, and do a little math to calculate the relative velocity. A passive radar like the one described in the RTL-SDR.com article linked above is quite different. Rather than painting a target with an RF signal, it relies on signals from other transmitters, such as terrestrial TV or radio outlets in the area. Two different receivers are used, both with directional antennas. One points to the area to be monitored, while the other points directly to the transmitter. By comparing signals reflected off moving objects received by the former against the reference signal from the latter, information about the distance and velocity of objects in the target area can be obtained.
The RTL-SDR test used a pair of cheap Yagi antennas for a nearby DVB-T channel to feed their KerberosSDR four-channel coherent SDR, a device we last looked at when it was still in beta. Essentially four SDR dongles on a common board, it’s available now for $149. Using it to build a passive radar might not save the neighborhood, but it could be a lot of fun to try.
If the great Samuel Clemens were alive today, he might modify the famous meteorological quip often attributed to him to read, “Everyone complains about weather forecasts, but I can’t for the life of me see why!” In his day, weather forecasting was as much guesswork as anything else, reading the clouds and the winds to see what was likely to happen in the next few hours, and being wrong as often as right. Telegraphy and better instrumentation made forecasting more scientific and improved accuracy steadily over the decades, to the point where we now enjoy 10-day forecasts that are at least good for planning purposes and three-day outlooks that are right about 90% of the time.
What made this increase in accuracy possible is supercomputers running sophisticated weather modeling software. But models are only as good as the raw data that they use as input, and increasingly that data comes from on high. A constellation of satellites with extremely sensitive sensors watches the planet, detecting changes in winds and water vapor in near real-time. But if the people tasked with running these systems are to be believed, the quality of that data faces a mortal threat from an unlikely foe: the rollout of 5G cellular networks.
Implementing PoE is made interesting by the fact that not every Ethernet device wants power; if you start dumping power onto any device that’s connected, you’re going to break things. The IEEE 802.3af standard states that the device which can source power should detect the presence of the device receiving power, before negotiating the power level. Only once this process is complete can the power sourcing device give its full supply. Of course, this requires the burden of smarts, meaning that there are many cheap devices available which simply send power regardless of what’s plugged in (passive PoE).
The brain of the upgrade is a TI TPS2378 Powered Device controller, which does the power negotiation. It sits on one of two new boards, with a rudimentary heatsink provided by some solar cell tab wire. The second board comprises the power interface, and consists of dual Schottky bridges as well a 58-volt TVS diode to deal with any voltage spikes due to cable inductance. The Ethernet transformer shown in the diagram above was salvaged from a dead Macbook and, after some enamel scraping and fiddly soldering, it was fit for purpose. For a deeper dive on Ethernet transformers and their hacked capabilities, [Jenny List] wrote a piece specifically focusing on Raspberry Pi hardware.
By harnessing the ferromagnetic properties of conductive thread, [Justin Chen] and [Shyam Gollakota] have proved the ability to store bit strings and 2D images through magnetization. The team used an embroidery machine to lay down thread in dense strips and patches, and then coded in ones and zeros by rubbing the threads with N and S neodymium magnets.
They didn’t use anything special, either, just this conductive thread, some magnets, and a Nexus 5 to read the data. Any phone with a magnetometer (so, most of them) could decode this type of binary data. The threads stay reliably magnetized for about a week and then begin to weaken. However, their tests proved that the threads can be re-magnetized over and over.
The team also created 2D images with magnets on a 9-patch made of conductive fabric. The images can be decoded piecemeal by a single magnetometer, or all at once by an array of them. Finally, the team made a glove with a magnetized patch of thread on the fingertip. They were able to get the phone to recognize six unique gestures with 90% accuracy, even with the phone tucked away in a pocket. See it in action in their demo video after the break.