Plant watering can sometimes be a pain... Here's a solution that automatically waters plants depending on the moisture of the soil, no timers required!
It works like this: when there is water in the reservoir and there is no water in the soil, the pump turns on, which transfers water from the reservoir to the plant.
This design is just a scale model, but the circuit it fully functional and can be used to water larger plants!
Step 1: Materials
Here's what you will need to build the electronic part of your watering system:
- 5v power supply (from USB charger)
- 1 NPN transistor (S9014)
- 1 PNP transistor (S9015)
- 2x 100k ohm resistors
- 1k ohm resistor
- 47 ohm resistor
- Stripboard or perfboard
- N-Channel MOSFET (SW2N60)
- 2 LEDs
- Aluminum Foil
- 4 binder clips (or paper clips)
- 1’ of tubing for pump
- Switch (optional)
- 5v submersible water pump
Some of these parts (like the water pump) were bought from eBay, while everything else I had lying around.
I also needed two glasses and some plywood to house the plants.
Step 2: Building the Circuit
Start by soldering the components onto the perfboard (or stripboard) according to the circuit diagram above. Be sure to connect extra wiring to the motor, sensor leads, and switch (if you use one).
I then used those mounting holes to secure the board to a piece of wood, this piece of wood will later be screwed onto the base of project.
The wires that went to the motor (or pump) were soldered on as well, and some heat shrink tubing was used to protect them.
Step 3: Building and Connecting the Sensor Electrodes
I used aluminum foil for the senor electrodes because aluminum oxide (the stuff that forms when aluminum is exposed to moisture) does not flake off (unlike rust).
These 1" strips of aluminum foil were bent with an inch overhang, then they were glued into the cups using spray adhesive, about 5mm away from each other.
I also tried steel and galvanized steel for electrodes with poor(er) results.
The electrodes were connected to the circuit by attaching the wires (coming from the circuit) to the foil using binder clips.
For the reservoir electrodes, be sure to leave some space between the electrodes and the bottom of the cup. This is so the motor properly stops before all of the water is depleted.
Step 4: Transferring the Plant(s) and Connecting Tubes
At this point I transferred some grass from the garden to the plant cup. I also attached a tube to the outlet of the pump and dropped it into the (now full of water) reservoir.
To secure the other end of the tube in the soil I used a small wooden dowel which I stuck to the very bottom of the cup.
Step 5: Making a Base and Securing the Cups
I felt like a base was missing, so I cut out a 10 by 4" piece of plywood and used some double sided tape to attach the cups on.
The circuit board was also attached with some screws.
Step 6: Extras!
I set the entire system up on my window sill and recorded the average height of the grass over 7 days. It grew quite fast, and at the end of the 7 days, the water was almost gone.
I suggest adding a bit of water-soluble fertilizer to speed up growth.
So, that's how to make your own plant watering system! Feel free to modify this design to fit your needs (like watering an actual plant!).