This palm sized circuit board monitors the moisture level of the
soil. Two pieces of copper wire are run from the circuit
board into the soil near a plant. The ends of the wire have galvanized
rods bolted on them which are placed into the soil (copper will
corrode). If the soil is deemed to be too dry a solenoid valve will
open. The solenoid valve is connected to my homes 3/4" white PVC
plumbing. All I've done is extended the PVC to reach all my garden
beds and trees. By drilling 1/8" holes in the PVC I've made a poor
mans irrigation system which has the smarts to not waste water.
drip hose 3/4" black poly is $0.60 foot and more difficult to obtain
my existing plumbing in the yard was all 3/4" PVC
no desire to get sucked into buy emitters, adapters, and special tools
irrigation controllers for multizone systems can cost up to $250
timer based irrigation systems will water when it is raining outside
desire to control everything
I am a cheap
Sputter - I am using a microcontroller which means the
soil moisture is being checked thousands of times a second.
This causes a situation when the soil begins to dry where the
solenoid is rapidly being turned on and off. I will
need to add some delays or use interrupts to prevent sputter.
Copper Probes - I've had good luck with galvanized probes
going into the earth to measure the soil moisture level. When I
had used copper the probes quickly oxidized causing the moisture
values to shift. Thus giving the plant more water than neccessary.
Location, Location, Location - Figuring out the length of
probe and distance to set them apart has been tricky. Just how
much water should a tree or plant get?
Sunlight - It is bad form to water plants during full
sunlight hours. If the water hits a leaf the sunlight can cause
a burn on the plant. The water also evaporates much faster during
the day. On a future version I could add a photo cell to detect
sunlight levels to allow watering during only in low light levels,
but avoid watering during full darkness and sunlight.
Power - I don't like having to find 120VAC power
everywhere I want to put a solenoid valve and controller. The
issue is that the solenoid valves for irrigation are usually
24VAC and I've been using 120VAC transformers to get the 24VAC.
In order to do standalone modules with their own solar cells I'd
need a small 12VDC transformer that can convert to 24VAC. A odd
Forcasting - Even though the wet controller has the brains
to not water the yard while rain is falling or recently after
rain. It does not know that a storm is nearby and there is a 80%
chance of thunderstorm.
Remote - Despite having the dry vs. wet logic I really
like the idea of controlling the system over the internet. Thus
allowing me to turn on or shutoff the home irrigation via my
cell phone. A future version would include some sort of wireless
networking to allow centralized remote management.
I have enough parts to make 12 of these boards. Each board sells
assembled for $50. I can include the solenoid valve and transformer
for a addition $30 bringing the total to $80.