Science Fair 11

1. MLIS Science Fair
Project Report
Electronic Soil Moisture Sensor
&
How to know how much water in soil?
Biology 11 & Physics 11
Dr. Adebanji & Ms. Shi
Group Member:
Nathanael Li Zhimo (Block C), Anna Dong Xinlu(Block A), Sheila Li
Jiale(Block A&C)
11 December 2021
Final Report 1

2. Part A
Question
How to know how much water in soil?
Introduction
In today's situation of increasingly scarce water resources, many developed countries still
use water-wasting irrigation methods, such as "lawn sprinklers". (Irrigation Water Use,
2013) It accounts for over 60% of the world's freshwater consumption (U.S. Geological
Survey, 2016). When the soil is poured with too much water, the soil will become
saturated and there is no way to absorb the excess water, which will cause the loss of
excess water source.
There are very few water resources on the earth, and the earth can’t wait, let alone we
can’t wait, we want to increase the maximum utilisation rate of water. So our team
decided to build an Electronic Soil Moisture Sensor for saving water. The useful reason is
to let people know exactly when to water through this, rather than watering uncontrollably
everywhere. (US EPA, OW, 2016)
The soil moisture sensor circuit has two metal probes that measure the electrical resistance
of the soil, or the difficulty of electricity flowing through the soil. It keeps a light-emitting
diode (LED) off when you plug them into wet soil, which has much lower resistance (or
Final Report 2

3. higher electrical conductivity) than dry soil. (Water conductivity - Lenntech, 2017) You
know you have to stop watering.
Variables
Independent variables - the amount of water
Dependent variables - the electronic resistance of the soil, the electrical conductivity
Control variables - The surface area of the probes, the distance between the probes
Hypothesis
For the end result of the experiment, If the soil is too dry, then the LED will turn on.
If the soil is wet, then the LED will stay off until the soil dries out again
Materials
For our experiment, we will need to buy...
- Breadboard
- 9 V battery
- 9 V battery snap connector
- CD4011 NAND gate integrated circuit (IC)
- 100 kΩ resistors (2) (brown, black, yellow, gold stripes)
- 470 Ω resistor (yellow, purple, brown, gold stripes)
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4. - Red LED
- 10 MΩ resistor
- Jumper wires (assorted)
- Alligator clip leads (2)
- Soil
- Popsicle sticks
- Aluminum foil
- Small block of stiff foam or wood
- Small plastic container with lid
- Power drill or hobby knife
- Safety goggles
- Hot glue or waterproof silicone sealant
We can buy it at/on ...
www.taobao.com
www.jd.com
www.amazon.com
www.ebay.com
Approximate cost 120 CNY
Procedure
For our experiment, we will...
Assembling the Circuit (Science Buddies)
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5. 1. 4011NAND gate, Rows1-7, straddling the middle of the breadboard, with
semicircular notch facing up
2. 10MΩ resistor, B2to(-)bus
3. 470Ω resistor, B3 to B11
4. Red LED, Long lead to A11, short lead to (-) bus
5. 100 kΩ resistor, C2, other lead free
6. 100 kΩ resistor, D1, other lead free
7. 9V battery and snap connector, Red lead to (+) bus black lead to (-) bus
8. Jumper wires (4), B1 to (+) bus, J1 to (+) bus, A7 to (-) bus, Left (+) bus to right
(+) bus
Testing the Circuit
Add different amounts of water to see if the conductivity and resistance will
change. Whether the LED stays off or on, as expected.
Setting up two groups
Group #1(use the Electronic Soil Moisture Sensor):
Always observe the state of the LED, according to the prompt and then water.
Group #2(do not use the Electronic Soil Moisture Sensor): Keep a fixed amount of
water poured every day.
Final Report 5

6. Results
The result of the
f
inal experiment is successfully veri
f
ied our initial guess
that when the soil is dry, the light bulb glows; when the soil becomes
wet, the light bulb goes out. This is because dry soil is an insulator and
does not conduct electricity. Therefore, we can judge whether the soil
contains water by the brightness of the bulb, and
f
inally achieve the
purpose of saving water. In addition, we also found that the brightness of
the bulb is determined by the amount of water. When we put three to
f
ive
drops of water into the soil, the light bulb
f
lickered and dimmed at the
same time. Continue to drip, and when it reaches 8 or 9 drops, the bulb
goes out. Because water droplets are not easy to accurately determine
the resistance of the soil, we used several di
ff
erent resistors and
determined resistances to calculate.
So we can see that when the resistance is 5.8, the bulb goes out.
In the course of this experiment, we also encountered many challenges.
For example, the soil dug from the campus at the beginning was too
moist to cause the small light bulbs to keep glowing because the
Final Report 6

7. resistance of the soil is greater than the resistance of the light bulbs. So
we dried the soil and experimented
again, but because the soil was too dry and agglomerated, the small bulb
still did not emit light. We guessed that the soil was too hard and the
entire circuit was in poor contact. So we smashed the soil and the
experiment was successful.
(Bulb 2.5v, battery 9v, Ohm's law: I=U/R)
The calculated results are summarised as shown in the
f
igure:
Discussion
Our experiment proved that our original hypothesis was correct.
Our experimental device could indeed turn on the light when the soil was dry and
turn off the light when the soil was wet. Our principle is to make a simple bulb
circuit, and this circuit is parallel circuit. We attach resistors to the left and right of
the bulb, and we stick one end of each resistor into the ground. Because the soil is dry
Final Report 7
Experiment
order
U/V R/Ω
The brightness of
the bulb
U/R=I
(1) 0.5 2.8 Not bright 0.18
(2) 1.0 4.5 Slightly bright 0.22
(3) 1.5 5.8 Dark 0.26
(4) 2.0 6.7 Darker 0.30
(5) 2.5 7.8 Normal light 0.32

8. and does not conduct electricity, the small bulb circuit is the path and the bulb emits
light. When water is added to the soil, the water conducts electricity, and the
resistance of the wet soil is less than the resistance of the bulb. The result is that the
bulb is shorted and the bulb goes out.
We use resistors because they can act as electrical appliances when the bulb goes out
to ensure that the circuit does not short-circuit; When the moisture in the soil is lost,
the soil becomes an insulator, and the circuit in which the light bulb is located
becomes a pathway, and the light bulb lights up again.
The formula we use is Ohm's law: "I=U/R" where I represents current in amperes, U
represents voltage in volts, and R represents resistance in ohms
Final Report 8
Circuit diagram
+
—

9. Conclusion
The purpose of our group's experiment is to prevent plants from dying due to water
shortage or overwatering. In order to achieve our goal, we adopted the circuit
detection method to detect, and the experimental results were good, indeed, the water
shortage or overwatering of plants could be detected to a certain extent.
In order to save the cost, we use a very simple device, because the device is very
simple, so we used to measure the dry degree of soil resistance is very small, lead to
soil can only lights in very dry, but for many plants, let them survive such extreme
environment, such as tulips, if excessive water will dry death The resistors should
normally and accurately detect whether the soil is wet or dry
In our daily life, this device can be used in the landscape and residential gardens, or
in the home plants can also use this device, in some parks, you can see automatic
watering devices, is the use of this principle.
References
Breadboards for Beginners. (n.d.). Adafruit Learning System. https://learn.adafruit.com/
breadboards-for-beginners
Fluhr, J., Bornkessel, A., & Berardesca, E. (2016). 20 Glycerol -Just a Moisturizer?
Biological and Biophysical Effects. http://www.scientificspectator.com/documents/
personal%20care%20spectator/
Glycerol%20a%20Moisturizer.pdf
Final Report 9

10. Irrigation Water Use | U.S. Geological Survey. (n.d.). Www.usgs.gov. Retrieved
December 11, 2021, from https://www.usgs.gov/special-topics/water-science-
school/science/irrigation-water-use?qt-science_center_objects=0%23qt-
science_center_objects
‌
Ohms Law Tutorial and Power in Electrical Circuits. (2018, April 28). Basic Electronics
Tutorials. https://www.electronics-tutorials.ws/dccircuits/dcp_2.html
Overwatered Houseplants: Fixing the damage - Binley Florist & Garden Center. (n.d.).
Www.binley
fl
orist.com. https://www.binley
fl
orist.com/index.php/news/
gardening-tips/216-overwatered-houseplants-
fi
xing-the-damage
‌‌
Pablo. (2019, November 22). Source and application of glycerol. USP 99.7 Glycerin
Refining Equipment.
https://www.glycerinrefine.com/news/source-and-application-of-glycerol/
Resistors - learn.sparkfun.com. (2019). Sparkfun.com. https://learn.sparkfun.com/
tutorials/resistors/all
‌
Soil Moisture Sensor. (n.d.). Www.elecrow.com. Retrieved December 11, 2021, from
https://www.elecrow.com/soil-moisture-sensor-p-509.html
‌
Final Report 10

11. “Soil Moisture Sensor SM150 - Sensors & Monitoring | Eijkelkamp.” Eijkelkamp.com,
2019, en.eijkelkamp.com/products/
fi
eld-measurement-equipment/soil-moisture-
sensor-sm150.html.
‌
“Wastewater Treatment: A Critical Component of a Circular
Economy.” Blogs.worldbank.org, blogs.worldbank.org/water/wastewater-
treatment-critical-component-circular-economy.
‌
“What Is Ohm’s Law?” Fluke.com,
fl
uke.com/en-us/learn/blog/electrical/what-is-ohms-
law. Accessed 11 Dec. 2021.
‌
Final Report 11