Soil Moisture Sensors, How Do They Work?

In a way, the magic of a soil moisture sensor’s functionality boils down to a simple RC circuit. But of course, in practice there is a bit more to it than that.¬†[rbaron] explains exactly how capacitive soil moisture sensors work simply, clearly, and concisely. He also shows, with a short video, exactly how their output changes in response to their environment, and explains how it informed his own sensor design.

At its heart, a moisture sensor measures how quickly (or slowly) a capacitor charges through a resistor, but in these sensors the capacitor is not a literal component, but is formed by two PCB traces that are near one another. Their capacitance — and therefore their charging rate — changes in response to how much water is around them. By measuring this effect on a probe sunk into dirt, the sensor can therefore indirectly measure the amount of water in the soil.

This ties into his own work on b-parasite: an open-source, all-in-one wireless soil moisture sensor (which was also a runner-up in our Earth Day contest) that broadcasts over BLE and even includes temperature readings. One thing to be mindful of if you are making your own PCBs or ordering them from a fab house is that passing current through metal in a moist environment is a recipe for oxidation, so it’s important not to expose bare traces to wet soil. A good coated PCB should avoid this problem, but one alternative we have seen proposed is to use graphite rods in place of metal.

Protect Your Tomatoes With A 9V Battery

Growing fresh vegetables at home is a popular pastime, even moreso in a year when we’ve all been locked inside. However pests can easily spoil a harvest, potentially putting a lot of hard work down the drain. [Matt] of [DIY Perks] isn’t one to give up his tomatoes without a fight, however, and came up with a solution to protect his plants.

The trick is to take advantage of the mildly conductive slime excreted by snails as they travel along the ground. To protect potted plants, [Matt] places two strips of copper tape around the perimeter of the pot, spaced about a centimeter apart. Each strip is connected to one terminal of a 9 V battery. When a snail attempts to cross the strips, it completes a circuit between the two, and the electrical current that flows irritates the snail, forcing it to retreat.

[Matt] notes that no snails were harmed in the making of the video, and that the solution is far kinder to the slimy critters than poisons or traps. He also goes so far as to demonstrate alternative solutions for garden beds, as well. We’ve more commonly seen [Matt] working with lighting, though it’s great to see he has a bit of a green thumb, too. Video after the break.

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Hardware Store Hydroponics

Science fiction movies often portray horticulture in the future, be it terrestrial or aboard spacecraft, with hydroponic gardens overflowing with leafy greens and brightly colored fruit. There is no soil, just clear water that hints at future-people creating a utopia of plant strains untethered from their earthly roots.

This star-faring food production method is not fiction if you forego the polycarbonate tubing, neon accent lights, and gardening robots. For his 2020 Hackaday Prize entry, [AVR] shares how he creates a bed for sixteen plants with parts sourced at a nearby home-improvement store. It may lack the visual pizzaz of the Hollywood versions, but it will grow soil-less crops on a hacker budget.

The starting point for this build is a sturdy wooden base. The PVC tubing and fence parts on top are light, but the water inside them will get heavy, and if you grow large plants, they become surprisingly heavy. Speaking of water, the sub-category of hydroponics this falls under is Nutrient Film Technique, or NFT, which uses a shallow stream of water laden with all the nutrients for plant growth. The square fence posts provide a flat top for mounting mesh cups where the plants grow and a flat bottom where the stream continuously flows. A basin and pump keep the plants refreshed and fed until they are ready for harvest.

Tend Your Garden… Again

In the early 1940s, several countries saw an incredible shift in agriculture. What were called “victory gardens” were being planted en masse by people from all walks of life, encouraged by various national governments around the world. Millions of these small home gardens sprang up to help reduce the price of produce during World War 2, allowing anyone with even the tiniest pot of soil to contribute to the war effort.

It’s estimated that in 1943 alone, victory gardens accounted for around one third of all vegetables produced in the United States. Since then, however, the vast majority of these productive gardens have been abandoned in favor of highly manicured, fertilized, irrigated turfgrass (which produces no food yet costs more to maintain), but thanks to the recent global pandemic there has been a resurgence of people who at least are curious about growing their own food again, if not already actively planting gardens. In the modern age, even though a lot of the folk knowledge has been lost since the ’40s, planting a garden of any size is easier than ever especially with the amount of technology available to help.

As someone who not only puts food on the table as a writer for a world-renowned tech website but also literally and figuratively puts food on the table as a small-scale market farmer, there are a few things that I’ve learned that I hope will help if you’re starting your first garden.

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Herb Garden Is Smarter Than The Average… Garden

After 13 days, the herbs are showing good signs of growth.

Herbs are a great way to spice up any dish. Often they don’t need much, meaning that it’s possible to grow a useful amount in a fairly compact area. [Sunyecz22] wanted to do just that, so built a convenient indoor herb garden, giving it some smarts along the way.

The project is built around an Arduino Mega, a venerable stalwart of the scene that comes in handy on projects requiring plenty of digital I/O. It’s paired with four soil moisture sensors, one per planter pot to keep an eye on water levels. The system also controls LEDs which provide light based on the time of day to help the herbs grow. Finally, a tidy 3D printed enclosure gives the project a neat, finished look.

It’s a build that’s a straightforward way to get into automatic plant maintenance, and leaves plenty of scope for future work. With the capable Arduino Mega on hand, it would be a cinch to upgrade to automatic watering down the track. We’ve seen similar builds before, too. Video after the break.

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Sow Your Seed Efficiently With This Multi-Way Drop Seeder

Anyone who has ever had to propagate small plants from seed will know that efficiently sowing seed can be a difficult process. Getting a consistent number of seed in each point while achieving any sort of speed is almost impossible, and as a result it becomes a tedious process. If only there were some means by which it could be automated, perhaps a way to do a whole tray at once!

Fortunately [Michael Ratcliffe] is at hand, with his tray-sized drop seeder. It consists of two sheets of acrylic each with a grid of holes, offset from each other by able to be brought into alignment with a lever. Seed is shaken over the upper surface until all the holes contain some, and then the lever is operated allowing it to drop through into the soil below. There is a matching dibber if required to push the required grid of holes in the soil.

It’s a simple yet ingenious gadget that genuinely will make the lives of horticulturalists a lot easier, even though it might not be perfect for all types of seed. He’s created a video which we’ve placed below the break, and should you wish to create the dibber we’ve already covered it.

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Building A Geodesic Dome Greenhouse

Greenhouses are a great way to improve conditions for your plants, and are an absolute necessity for any serious gardening in colder climates. When the time came for [gentleworks] to build a new greenhouse, rather than going with a conventional design, they decided to go with a geodesic dome instead.

The greenhouse uses a few techniques that will be unfamiliar to those used to run-of-the-mill carpentry. The individual cedar struts meet at a series of hubs, constructed out of short lengths of Schedule 80 PVC pipe. The struts are attached to the pipe with steel straps, screwed into place. This doesn’t give the strongest of holds, but as most of the loads on the struts are compressive in nature, it works well in practice.¬†Plastic sheeting is used as a covering to help let in plenty of light while keeping the cold out. The greenhouse is also heated, and can maintain a 40 deg F temperature differential with 14,000 BTUs.

It’s a build that has us wanting to throw up a dome or two in our own backyard. We’ve seen other geodesic structures before; if you’re working on one yourself, be sure to drop us a line.