Ultra-Low Power Soil Moisture Sensor

March 18, 2025 by Bryan Cockfield 13 Comments

Electricity can be a pretty handy tool when it stays within the bounds of its wiring. It’s largely responsible for our modern world and its applications are endless. When it’s not running in wires or electronics though, things can get much more complicated even for things that seem simple on the surface. For example, measuring moisture in soil seems straightforward, but corrosion presents immediate problems. To combat the problems with measuring things in the natural world with electricity, [David] built this capacitive soil moisture sensor which also has the benefit of using an extremely small amount of energy to operate.

The sensor is based on an STM32 microcontroller, in this case one specifically optimized for low-power applications. The other low-power key to this build is the small seven-segment e-ink display. The segments are oriented as horizontal lines, making this a great indicator for measuring a varying gradient of any type. The microcontroller only wakes up every 15 minutes, takes a measurement, and then updates the display before going back to sleep.

To solve the problem resistive moisture sensors have where they’re directly in contact with damp conditions and rapidly corrode, [David] is using a capacitive sensor instead which measures a changing capacitance as moisture changes. This allows the contacts to be much more isolated from the environment. The sensor has been up and running for a few months now with the coin cell driving the system still going strong and the house plants still alive and properly watered. Of course if you’re looking to take your houseplant game to the next level you could always build a hydroponics system which automates not only the watering of plants but everything else as well.

Turning Down The Noise On SMPS

March 17, 2025 by Bryan Cockfield 13 Comments

On paper, electricity behaves in easy-to-understand, predictable ways. That’s mostly because the wires on the page have zero resistance and the switching times are actually zero, whereas in real life neither of these things are true. That’s what makes things like switch-mode power supplies (SMPS) difficult to build and troubleshoot. Switching inductors and capacitors tens or hundreds of thousands of times a second (or more) causes some these difficulties to arise when these devices are built in the real world. [FesZ Electronis] takes a deep dive into some of the reasons these difficulties come up in this video.

The first piece of electronics that can generate noise in an SMPS are the rectifier diodes. These have a certain amount of non-ideal capacitance as well as which causes a phenomenon called reverse current, but this can be managed by proper component choice to somewhat to limit noise.

The other major piece of silicon in power supplies like this that drives noise are the switching transistors. Since the noise is generally caused by the switching itself, there is a lot that can be done here to help limit it. One thing is to slow down the amount of time it takes to transition between states, limiting the transients that form as a result of making and breaking connections rapidly. The other, similar to selecting diodes, is to select transistors that have properties (specifically relating to inherent capacitances) that will limit noise generation in applications like this.

Of course there is a lot more information as well as charts and graphs in [FesZ]’s video. He’s become well-known for deep dives into practical electrical engineering topics like these for a while now. We especially like his videos about impedance matching as well as a more recent video where he models a photovoltaic solar panel in SPICE.

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A DIY Proximity Sensor, Using Just Scrap Parts And Software

July 1, 2024 by Donald Papp 7 Comments

[mircemk] shows how to create a simple non-contact proximity sensor using little more than an Arduino Nano board, and a convenient software library intended to measure the value of capacitors.

The prototype has a threshold set via potentiometer for convenience.

The basic idea is that it’s possible to measure a capacitor’s capacitance using two microcontroller pins and the right software, so by using a few materials to create an open-style capacitor, one can monitor it for changes and detect when anything approaches enough to alter its values past a given threshold, creating a proximity sensor.

The sensor shown here is essentially two plates mounted side-by-side, attached to an Arduino Nano using the Capacitor library which uses just two pins, one digital and one analog.

As configured, [mircemk]’s sensor measures roughly thirty picofarads, and that value decreases when approached by something with a dielectric constant that is different enough from the air surrounding the sensor. The sensor ignores wood and plastic, but an approaching hand is easily detected. The sensor also detects liquid water with similar ease, either in the form of pooled liquid, or filled bottles.

We’ve also seen a spring elegantly used as a hidden touch sensor that works through an enclosure’s wall by using similar principles, so the next time you need a proximity or touch-sensitive sensor in a project, reaching for the junk box might get you where you need to go. Watch [mircemk]’s sensor in action in the video, just below the page break.

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Cascade Failures, Computer Problems, And Ohms Law: Understanding The Northeast Blackout Of 2003

February 25, 2022 by Ryan Flowers 16 Comments

We’ve all experienced power outages of some kind, be it a breaker tripping at an inconvenient time to a storm causing a lack of separation between a tree and a power line. The impact is generally localized and rarely is there a loss of life, though it can happen. But in the video below the break, [Grady] of Practical Engineering breaks down the Northeast Blackout of 2003, the largest power failure ever experienced in North America. Power was out for days in some cases, and almost 100 deaths were attributed to the loss of electricity.

[Grady] goes into a good amount of detail regarding the monitoring systems, software simulation, and contingency planning that goes into operating a large scale power grid. The video explains how inductive loads cause reactance and how the effect exacerbated an already complex problem. Don’t know what inductive loads and reactance are? That’s okay, the video explains it quite well, and it gives an excellent basis for understanding AC electronics and even RF electronic theories surrounding inductance, capacitance, and reactance.

So, what caused the actual outage? The complex cascade failure is explained step by step, and the video is certainly worth the watch, even if you’re already familiar with the event.

It would be irresponsible to bring up the 2003 outage without talking about the Texas ERCOT outages just one year ago– an article whose comments section nearly caused a blackout at the Hackaday Data Center!

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Pour Yourself A Glass Of 100,000 Volts

August 5, 2020 by Tom Nardi 15 Comments

You’d be hard pressed to find a hacker or maker who doesn’t have a soft spot for the tantalizing buzz and snap of a high voltage spark gap, but it remains the sort of project that most of us don’t take on personally. There’s a perceived complexity in building a device capable of shooting a proper spark through several inches of open air, with connotations of exotic components and massive hand-wound coils. Plus, nobody wants to inadvertently singe off their eyebrows.

While the latest video from [Jay Bowles] might not assuage anyone’s fear of performing impromptu electrolysis, it does at least prove that you don’t need to have a laboratory full of gear to produce six figure voltages. In fact, you don’t even need much in the way of electronics: the key components of this DIY Marx generator are made with little more than water and some household items.

This is made possible by the fact that the conductivity of water can be changed depending on what’s been dissolved into it. Straight tap water is a poor enough conductor that tubes of it can be used in place of high voltage resistors, while the addition of some salt and a plastic insulating layer makes for a rudimentary capacitor. You’ll still need wires to connect everything together and some bits of metal to serve as spark gaps, but nothing you won’t find lurking in the parts bin.

Of course, water and a smattering of nails won’t spontaneously generate electricity. You need to give it a bit of a kick start, and for that [Jay] is using a 15,000 volt DC flyback power supply that looks like it may have been built with components salvaged from an old CRT television. While the flyback transformer alone could certainly generate some impressive sparks, this largely liquid Marx generator multiplies the input voltage to produce a serious light show.

We’re always glad to see a new video from the perennially jovial [Jay] come our way. While his projects might not always be practical in the strictest sense, they never fail to inspire a lively discussion about the fascinating applications of high voltage.

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Solving The Mysteries Of Grounding While Improving A Power Supply

February 4, 2020 by Bryan Cockfield 22 Comments

Grounding problems and unwanted noise in electrical systems can often lead to insanity. It can seem like there’s no method to the madness when an electrical “gremlin” caused by one of these things pops its head out. When looking more closely, however, these issues have a way of becoming more obvious. In a recent video, [Fesz Electronics] shows us how to investigate some of these problems by looking at a small desktop power supply, modelling it in LTSpice, and reducing the noise on the power supply’s output.

While everything in this setup is properly grounded, including the power supply and oscilloscope, the way the grounding systems interact can contribute to the high amount of noise. This was discovered by isolating the power supply from earth ground using electrical tape (not recommended as a long-term solution) and seeing that the noise was reduced. However, the ripple increased substantially, so a more permanent fix was needed. For that, the power supply was modelled in LTSpice. This is where a key discovery was made: since all the parts of the power supply aren’t ideal, noise can be introduced from the actual real-life electrical behavior of some of the parts. In this case, it was non-ideal capacitance in the transformer.

According to the model, this power supply could be improved by adding a larger capacitor across the output leads, and also by increasing their inductance. A large capacitor was soldered in the power supply and an iron ferrule was added, which decreased the noise level from 100 mV to around 20. Still not perfect, but a much needed improvement to the simple power supply. If, on the other hand, you want to make sure you eliminate that transformer’s capacitance completely, you can always go with a transformerless power supply. That carries other risks, though.

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Everything You Didn’t Know You Were Missing About Bias Tees

June 26, 2018 by Dan Maloney 23 Comments

Do you need a bias tee? If you want to put a DC voltage on top of an RF signal, chances are that you do. But what exactly are bias tees, and how do they work?

If that’s your question, [W2AEW] has an answer for you with this informative video on the basics of bias tees. A bias tee allows a DC bias to be laid over an RF signal, and while that sounds like a simple job, theory and practice often deviate in the RF world. The simplest bias tee would have a capacitor in series with the RF input and output to pass AC but block DC from getting out the input, and a DC input with a series inductance to prevent RF from getting into the DC circuit. Practical circuits are slightly more complicated, and [W2AEW] covers all you need to know about how real-world bias tees are engineered. He also gives some use cases for bias tees, from sending DC signals up a feed line to control an antenna tuner or rotator to adding a DC bias to a high-speed serial line.

It’s an interesting circuit, and we learned a lot, which is par for the course with [W2AEW]’s videos. Check out some of his other offerings, like a practical guide to the mysteries of Smith charts, or his visualization of how standing waves work.

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