Around the Hackaday bunker, any plant other than a cactus has a real chance of expiring due to thirst. Perhaps we should build some of [MakersFunDuck]’s Moisture Duck boards. As you can see in the video below, the simple PCB with an ATtiny13A tells you when it is time to water the plants. The video also covers several exotic methods of determining the watering status, some of which are pretty complex.
The board is simple because the operation of the device is simple. A fixed resistor creates a voltage divider with the soil, and dry soil has higher resistance than moist soil. A pot sets a threshold, and the microcontroller measures the voltages.
Of course, if you can’t remember to water the plants, you probably can’t remember to change batteries either. So the device sleeps most of the time, and only wakes up every eight seconds to conserve battery. It would be nice to alarm on a low battery, and, honestly, we would probably have made the sleep time longer.
The video covers how he minimizes corrosion, but we aren’t sure how well the board will survive in damp soil, but with a little protection, it might last a while. Besides that, you could probably just consider them almost disposable.
Ever wanted to measure soil moisture? Common “soil moisture meter module arduino raspberry compatible free shipping” PCBs might deceive you with their ascetic looks. Today, [Raphael (@rbaron_)] is here to teach us (Twitter, unrolled) what it takes to build a soil-embedded sensor that can actually survive contact with a plant.
As the picture might hint, waterproofing is of paramount importance, and soldermask doesn’t quite cut it. Raphael describes his journey of figuring out approaches and coatings that would last, starting from simply using nail polish, and ending with the current option – a rotisserie-like device that rotates sensors as the coating applied to them dries, mitigating a certain kind of structural failure observed long-term. With plenty of illustrative pictures and even a video of the rotisserie device in action, you’ll quickly learn things that took time and effort for Raphael to figure out.
Soil sensors are handy things, but while sensing moisture is what they do, how they handle that data is what makes them useful. Ensuring usefulness is what led [Maakbaas] to design and create an ESP32-based soil moisture sensor with wireless connectivity, deep sleep, data logging, and the ability to indicate that the host plant needs watering both visually, and with a push notification to a mobile phone.
The visual notification part is pretty nifty, because [Maakbaas] uses a small flip-dot indicator made by Alfa-Zeta. This electromechanical indicator works by using two small coils to flip a colored disk between red or green. It uses no power when idle, which is a useful feature for a device that spends most of its time in a power-saving deep sleep. When all is well the indicator is green, but when the plant needs water, the indicator flips to red.
The sensor itself wakes itself up once per hour to take a sensor measurement, which it then stores in a local buffer for uploading to a database every 24 measurements. This reduces the number of times the device needs to power up and connect via WiFi, but if the sensor ever determines that the plant requires water, that gets handled immediately.
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.
It’s not infrequent that we see the combination of moisture sensors and water pumps to automate plant maintenance. Each one has a unique take on the idea, though, and solves problems in ways that could be useful for other applications as well. [Emiliano Valencia] approached the project with a few notable technologies worth gleaning, and did a nice writeup of his “Autonomous Solar Powered Irrigation Monitoring Station” (named Steve Waters as less of a mouthful).
Of particular interest was [Emiliano]’s solution for 3D printing a threaded rod; lay it flat and shave off the top and bottom. You didn’t need the whole thread anyway, did you? Despite the relatively limited number of GPIO pins on the ESP8266, the station has three analog sensors via an ADS1115 ADC to I2C, a BME280 for temperature, pressure, and humidity (also on the I2C bus), and two MOSFETs for controlling valves. For power, a solar cell on top of the enclosure charges an 18650 cell. Communication over wireless goes to Thingspeak, where a nice dashboard displays everything you could want. The whole idea of the Stevenson Screen is clever as well, and while this one is 3D printed, it seems any kind of stacking container could be modified to serve the same purpose and achieve any size by stacking more units. We’re skeptical about bugs getting in the electronics, though.
We have all been stuck inside for too long, and maybe that’s why we have recently seen a number of projects attempting to help humans take better care of their housemates from Kingdom Plantae. To survive, plants need nutrients, light, and water. That last one seems tricky to get right; not too dry and not drowning them either, so [rbaron’s] green solder-masked w-parasite wireless soil monitor turns this responsibility over to your existing home automation system.
The “w” in the name is for WiFi as the built-in ESP-32 module then takes the moisture reading and sends an update wirelessly via MQTT. Depending on the IQ of your smart-home setup, you could log the data, route an alert to a cellphone, light up a smart-bulb, or even switch on an irrigation system.
[rbaron] has shared a string of wireless hacks, controlling the A/C over Slack and a BLE Fitness Tracker that inspired more soldering than jogging. We like how streamlined this solution is, with the sensor, ESP-32 module, and battery all in a compact single board design. Are you asking yourself, “but how is a power-hungry ESP-32 going to last longer than it takes for my geraniums to dry out?” [rbaron] is using deep sleep that only consumes 15uA between very quick 500ms check-ins. The rechargeable LIR2450 Li-Ion coin cell shown here can transmit a reading every half hour for 90 days. If you need something that lasts longer than that, use [rbaron]’s handy spreadsheet to choose larger batteries that last a whole year. Though, let’s hope we don’t have to spend another whole year inside with our plant friends.
We may never know why the weeds in the cracks of city streets do better than our houseplants, but hopefully, we can keep our green roommates alive (slightly longer) with a little digital nudge.
Soil moisture sensors are cheap and easy to interface with, to the point that combining one with an Arduino and blinking an LED when your potted plant is feeling a bit parched is a common beginners project. But what about on the long term? Outside of a simple proof of concept, what would it take to actually read the data from these sensors over the course of weeks or months?