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.

Your Plants Can Take Care Of Themselves Now

One of [Sasa]’s life goals is to be able to sit back in his home and watch as robots perform all of his work for him. In order to work towards this goal, he has decided to start with some home automation which will take care of all of his house plants for him. This project is built from the ground up, too, and is the first part of a series of videos which will outline the construction of a complete, open-source plant care machine.

The first video starts with the sensors for the plants. [Sasa] decided to go with a completely custom module based on the STM32 microcontroller since commercial offerings had poor communications designs and other flaws. The small board is designed to be placed in the soil, and has sensors for soil moisture as well as other sensors for amount of light available and the ambient temperature. The improvements over the commercial modules include communication over I2C, allowing a large number of modules to communicate over a minimum of wires and be arranged in any way needed.

For this build everything is open-source and available on [Sasa]’s GitHub page, including PCB layouts and code for the microcontrollers. We’re looking forward to the rest of the videos where he plans to lay out the central unit for handling all of these sensors, and a custom dashboard for controlling them as well. Perhaps there will also be an option for adding a way to physically listen to the plants communicate their needs as well.

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Compile A Hydroponics System From Source

Tending to a garden is usually a rewarding endeavor, as long as there is good soil to work with. If there isn’t, it can either get frustrating quickly having to deal with soils like sand or hard clay, or it can get expensive by having to truck in compost each year. Alternatively, it’s possible to set up systems of growing plants that don’t need any soil at all, although this requires an automated system otherwise known as hydroponics to manage water and nutrients sent to the plants.

This setup by [Kyle] is unique in that it uses his own open-source software which he calls Mycodo to control the hydroponic system. It is loaded onto a Raspberry Pi 4 (which he notes can now be booted from a USB drive instead of an SD card) which controls all of the peripherals needed for making sure that the water has the correct amount of nutrients and chemical composition.

The build is much more than just a software control panel, though. [Kyle] walks through every part of setting up a small hydroponic system capable of effectively growing 15-20 plants indoors. He grows varieties of lettuce and basil, but this system can work for many more types of plants as well. With just slight variations, a similar system can not only grow plants like these, but fish as well.

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Hearing Plants Giggle Is Just As Creepy As You Think

While best known for Charlie and the Chocolate Factory, Roald Dahl wrote quite a few similarly oddball stories in his time. One of them, The Sound Machine, is about a device that allowed the user to hear the anguished screams of trees as they were cut down. Sounds kind of weird to us, but [Roni Bandini] liked the idea so much he decided to build his own version.

Now to be fair, the device doesn’t only scream in pain. In fact, most of the time it should be emitting laughs and happy noises. Using a moisture sensor driven into the soil of a plant’s pot, the device uses these audio cues to tell you the relative health of your leafy friend. So assuming you’ve got any sort of green thumb at all, things should be fine.

But once the soil gets too dry and the device determines the plant is in “pain”, things take a turn for the worse. We suppose it doesn’t technically scream out so much as grunt like a zombie, but it’s still not a noise we’d want to hear while walking through the house at night. Luckily, it seems you need to hit the button on the front of the 3D printed enclosure to get it to play the appropriate sound track from its DFPlayer module.

Personally we’d rather build something that makes sure the plants are being taken care of automatically than a gadget that cries out in anguish to remind us that we don’t know what we’re doing. But hey, everyone gets inspired in their own way.

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Simulate Climate With An Arduino

Greenhouses create an artificial climate specifically suited to the plants you want to grow. It’s done by monitoring conditions like temperature and humidity, and making changes using things like vents, fans, irrigation, and lighting fixtures to boost temperature. But how do you know when it’s time to up the humidity, or vent some of the heat building up inside? The easy way is to use the Arduino-powered Norman climate simulator from [934Virginia] which leverages data from different locations or times of year based on NOAA weather data to mimic a particular growing environment.

Norman relies on a simple input of data about the target location, working from coordinates and specified date ranges to return minimum/maximum values for temperature and humidity weather conditions. It makes extensive use of the Dusk2Dawn library, and models other atmospheric conditions using mathematical modeling methods in order to make relatively accurate estimates of the target climate. There are some simulations on the project’s Plotly page which show what this data looks like.

This data is used by [934Virginia’s] Arduino library to compare the difference between your target climate and actual sensor readings in your greenhouse. From there you can make manual changes to the environment, or if you’re luck and already have an Arduino-based greenhouse automation system the climate adjustments can be done automatically. The project is named after Norman Borlaug, a famous soil scientist and someone worth reading about.

Editor’s Note: This article has been rewritten from the original to correct factual errors. The original article incorrectly focused on replicating a climate without the use of sensors. This project does require sensors to compare actual greenhouse conditions to historic climate conditions calculated by the library. We apologize to [934Virginia] for this and thank them for writing in to point out the errors.

Images courtesy of Wikimedia Commons.

A Farmer’s Guide To Technology

One of the hardest aspects of choosing a career isn’t getting started, it’s keeping up. Whether you’re an engineer, doctor, or even landscaper, there are always new developments to keep up with if you want to stay competitive. This is especially true of farming, where farmers have to keep up with an incredible amount of “best practices” in order to continue being profitable. Keeping up with soil nutrient requirements, changing weather and climate patterns, pests and other diseases, and even equipment maintenance can be a huge hassle.

A new project at Hackerfarm led by [Akiba] is hoping to take at least one of those items off of farmers’ busy schedules, though. Their goal is to help farmers better understand the changing technological landscape and make use of technology without having to wade through all the details of every single microcontroller option that’s available, for example. Hackerfarm is actually a small farm themselves, so they have first-hand knowledge when it comes to tending a plot of land, and [Bunnie Huang] recently did a residency at the farm as well.

The project strives to be a community for helping farmers make the most out of their land, so if you run a small farm or even have a passing interest in gardening, there may be some useful tools available for you. If you have a big enough farm, you might even want to try out an advanced project like an autonomous tractor.

Does WiFi Kill Houseplants?

Spoiler alert: No.

To come to that conclusion, which runs counter to the combined wisdom of several recent YouTube videos, [Andrew McNeil] ran a pretty neat little experiment. [Andrew] has a not inconsiderable amount of expertise in this area, as an RF engineer and prolific maker of many homebrew WiFi antennas, some of which we’ve featured on these pages before. His experiment centered on cress seeds sprouting in compost. Two identical containers were prepared, with one bathed from above in RF energy from three separate 2.4 GHz transmitters. Each transmitter was coupled to an amplifier and a PCB bi-quad antenna to radiate about 300 mW in slightly different parts of the WiFi spectrum. Both setups were placed in separate rooms in east-facing windows, and each was swapped between rooms every other day, to average out microenvironmental effects.

After only a few days, the cress sprouted in both pots and continued to grow. There was no apparent inhibition of the RF-blasted sprouts – in fact, they appeared a bit lusher than the pristine pot. [Andrew] points out that it’s not real science until it’s quantified, so his next step is to repeat the experiment and take careful biomass measurements. He’s also planning to ramp up the power on the next round as well.

We’d like to think this will put the “WiFi killed my houseplants” nonsense to rest – WiFi can even help keep your plants alive, after all. But somehow we doubt that the debate will die anytime soon.

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