Solar Powered Circuit Waters Your Plants


If you want your plants to stay healthy, you need to make sure they stay watered. [Dimbit] decided to build his own solar powered circuit to help automatically keep his plants healthy. Like many things, there is more than one way to skin this cat. [Dimbit] had seen other similar projects before, but he wanted to make his smarter than the average watering project. He also wanted it to use very little energy.

[Dimbit] first tackled the power supply. He suspected he wouldn’t need much more than 5V for his project. He was able to build his own solar power supply by using four off-the-shelf solar garden lamps. These lamps each have their own low quality solar panel and AAA NiMH cell. [Dimbit] designed and 3D printed his own plastic stand to hold all of the solar cells in place. All of the cells and batteries are connected in series to increase the voltage.

Next [Dimbit] needed an electronically controllable water valve. He looked around but was unable to find anything readily available that would work with very little energy. He tried all different combinations of custom parts and off-the-shelf parts but just couldn’t make something with a perfect seal. The solution came from an unlikely source.

One day, when [Dimbit] ran out of laundry detergent, he noticed that the detergent bottle cap had a perfect hole that should be sealable with a steel ball bearing. He then designed his own electromagnet using a bolt, some magnet wire, and a custom 3D printed housing. This all fit together with the detergent cap to make a functional low power water valve.

The actual circuit runs on a Microchip PIC microcontroller. The system is designed to sleep for approximately nine minutes at a time. After the sleep cycle, it wakes up and tests a probe that sits in the soil. If the resistance is low enough, the PIC knows that the plants need water. It then opens the custom valve to release about two teaspoons of water from a gravity-fed system. After a few cycles, even very dry soil can reach the correct moisture level. Be sure to watch the video of the functioning system below.

28 thoughts on “Solar Powered Circuit Waters Your Plants

  1. Neat idea. I was toying with using one of these – for a similar project. The idea I had was to use a sealed bottle full of water, gravity fed, with the air pump to allow a controlled amount of air in to the bottle (thus dispensing the water). So far the idea hasn’t left the drawing board.

    1. 3V MINI pump motor 400ma seems a bit of an overkill. Great idea though . You only need something electronic to open a small hole for a fraction of a second and air pressure will do the job for you.

      1. I had a play with that idea. It’s really hard not to have constant drips come out, and don’t forget that you don’t get away from having the exact same pressure differential as you would under the water.
        That pump’s a good find though.

  2. Yeah that’s kind of clever but clearly he didn’t look real hard. There are plenty of “motorized ball valve” (that’s your search term) on eBay that run at about 12VDC 80mA; they’re a little DC electric motor and plastic geartrain bolted to a brass mains-pressure-rated ball-valve. More expensive than his hand-wound coil and 3D-printed stuff but cheaper than a 24VAC solenoid (with much less power consumption!) and readily obtainable by those without 3D printers.

    And if you’re watering something other than a pot, dribbling in a teaspoonful is not a good approach. The water needs to soak deep to make the roots grow deep.

    1. In the interests of fairness, I should probably note that motorised valves (and equivalent hackjobs with servos) are not power-fail-safe. Solenoid-driven valves (hacky or commercial) will at least shut off if the power goes out.

  3. FTA: ” If the resistance is low enough, the PIC knows that the plants need water.” Shouldn’t it be “if the resistance is high enough?” Watering lowers soil resistance.

  4. The probe should use AC, or at least, invert the polarity of the cathode/anode at each cycle, to prevent early probe corrosion. If the probe corrodes, then the measure of resistance will not be accurate.

  5. Nice build, I like to see a project where parts are choosen according to project needs, many people would build this with Arduino or even RasPi and waste resources, power and space. 1$ uC is an excellent choice.

  6. Beautiful work with the valve. I am wondering if a hamster water bottle could be persuaded to react to a magnetic field, as essentially you get ready made a reservoir coupled to a ball valve. Maybe a vibrating motor from a phone could be used to rattle the ball enough to release a few ml.

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