5 Soil moisture detector circuits and automatic controller

This is 5 soil moisture detector circuit projects, can build easy with PCB No.5 circuits and alarm with LED and buzzer, and controller as water for plants

I like planting trees, because trees are more useful to us. However, I always have problems with moisture content of soil,Each plant needs water is not as same. Watering or soil moisture is not good. May cause damage to our trees. With these problems, I think the electronic system to solve this problem. For example, to check moisture level of the soil. We see from the outside, may not be good enough. Sometimes we see that the soil is dry.But it may be appropriate to plant moisture that, when we add water. It may be possible to root rot. To determine these characteristics. It saves water, too. I collected several circuits below.

1. Automatic watering a tree

A trees should be taken care of as well. This circuit allows for watering trees, can be done automatically.When soil moisture levels decrease, to values that are defined.(Which can be determined by the resistance of R1.) A relay RY1 starts.This relay can be used to control the alarm, or Open water valve for watering plants.The probe used is a large copper wire, or a metal rod with a length of about 120 mm.
On the end of each probe, attached to the insulation sheet, which is right size.(about 40 x 20 mm.) The probe should be straight and parallel bars, each separated by 15 mm. The VR1 to customize the sensitivity of the circuit.

Automatic watering a tree

Other circuits are recommended.:
Water pump controller circuit

2. Moisture sensor circuit

This Check this dry soil circuit or soil moisture meter For the Blind. Because it will alert on clay. Circuit has less detail. It production the low frequency pulse, the IC CMOS CD4001 circuits. is primary device,internal structure consists of NOR Gate.When added to RC circuit will be on low frequency oscillator. It is divided into two series, the first low frequency pulse generator. Then sent to another set. , A set of audio source through the C4 and then out to the speakers.You can apply the display devices as needed. Special about this circuit is to use solar cells as power supply to the circuit.Use only probes. Into the soil, we want to examine.

Moisture sensor circuit

3. Moisture Activated Relay by Bipolar Transistor

Today we try to build warn the moistness or Moisture Activated better. Or do go to use be warn it rains. Because of be the circuit is simple. Follow the circuit will think use Bipolar Transistor just one only. When measure touch the moistness make the electric current flows through to pin B of Q1 get then make it works. The Relay as a result work apply the work controls electric other appliances. By the rapidity of this circuit can control with R2 – 1M. If you use power supply the size is 6V-9V. Should use Relay 6V-9V resistance coil sizes about 500ohm. For the transistor use 2N2222 or BC549 or C1815 etc. Then make the circuit s work well sir.

Moisture Activated Relay by Bipolar Transistor

4. LED warning water the plants with ic 4093

Electronic users love trees. But no time and work and forget Enjoy water the plants.So the trees dry out.This circuit solves this problem.It also allows us to not water the plants with too often.
Operation of the circuit. When the supply to the circuit. IC1 / 1 (IC 4093) will work together R1, R2, D1 and C2 is the Oscillator generator.The output at Pin 11 is a rectangular pulse to IC1/2.To return the logic state is out of the opposite pin 3.In addition, the signal from the pin 11 will be issued to the temple ground. be test point A and test point B.It will be resistance.Make a signal to stimulate IC1/3, IC1/4.Which is parallel to the current output is high enough to make the LED light.The signal from IC1 / 2 VR1 is a fine stream that flows into IC1 / 3 and IC1 / 4. To suit the soil to measure.If the ground for us to measure the humidity Li LED1 will light extinguishes.And if the ground is dry LED1 light depending on adjustments VR1.
LED warning water the plants with ic 4093

5. Simple soil moisture alarm


The tree is very necessary for humans. Because can clean waste air, as a food, housing, medicine, etc., We should tree planting as well.
Water is necessary for the trees. But the trees should be watered properly. If too much water rotten the trees, but less water to the trees wither, may be dead.

As a electronic projects creator,This project would help solve this problem. It will alarm us to watering the plants when the soil is dry. or lack of water for a long time. and can be customized to detect soil moisture levels as well.

The working principle
See various transistors in circuit as show Figure 1 then do not go away due to think so really difficult. They not have any thing look at! below…

When we connect a battery to provide circuit. The C6 is a first components that received before. To filter voltage to smooth and regularity of voltage before to others section.
Figure 1 Simple soil moisture alarm circuit.

Then, both transistors Q1 and Q2 are connected into the astable multivibrator circuit to produce a triangle wave that has frequency about 4 kHz. This frequency is set from R2 x C2 or R3 x C3 (R2 = R3 and C2 = C3 must same size) By have R1 and R4 are current limiter through a collector of transistor.

The frequency will pass into R5, R6 and C3 before to base of Q3 and Q4 that connected as complementary signal amplifier. Next, signal is amplified then out of to collector of both Q3 and Q4.

Now, we have signal in 2 ways are (1) pass to C5 then come to measure point. and (2) Come to piezo speaker. Which will pass to any way depends on moisture stage now be wet or dry.

In the first event of still a moisture or wet so compare with low resistance. signal so pass to this way to as bias voltage to Q5 , by has a VR1 is adjusting sensitivity in ??????checking the soil moisture. Then when Q5 is biased to base of Q5. So has conducting voltage from power supply through to R8 to collector. Next, out to emitter of Q5 to ground. so piezo speaker does not loud sound.

After that, when soil dry at sensor point has higher resistance. or compare that not connect together. The signal at collector of Q3 and Q4 so come to the piezo-speaker (BZ1) passes to collector of Q6. Which now, base of Q6 receive the bias voltage passes from R8.

Therefore, the signal passed to collector, so flow to ground and can flow through the emitter to piezo speaker. so emit sound we hear. When come to this point as the end working is enough.

How to builds.
This projects has a small size PCB as shown in Figure 2, So must be careful to create as Figure 3 is How to assemble circuits that show all components layout Important: Do not put the wrong position or switch legs. Otherwise, this project will not work. and the the checking point, should use cord reinvigorate to be plugged deep and not rocking too easy.

Figure 2 is the PCB layout of this projects

Figure 3 is the components layout of the simple soil moisture alarm project.

How to use its
We test easily this project, by connects the 1.5V battery to batter holder, then separate the checking point apart. we will hear shrill tone out to the piezo speaker. But when we caught the two tangent wires, so this sound stop once. Show that this project is working properly.
And then, how to apply them just simply plug the checking point in the flower pot. Moderately deep root of the tree. Then adjust VR1 to suit the soil conditions. This is just use it. If you think that weak sound. can rise the voltage of power supply But under 9 volts.

The list of all components.
Resistors ¼ W + 5%
R1, R4——————–22K
R2, R3——————–220K
R5, R6, R8—————100K
VR1—Trimmer POT____100K potentiometer.
The capacitors
C1———————10uF 16V___Electrolytic capacitors
C2, C3—————-820pF 50V___Polyester capacitors
C4————————-470pF 50V___Polyester capacitors
C5————————-1uF 16V___Electrolytic capacitors
C6————————-0.1uF(104)50V___Polyester capacitors
The semiconductor
D1————————1N4148___0.75A 200V Diode
Q1-Q3, Q5-Q6———BC550C__45V 100mA NPN Transistor
Q4————————BC560___50V 100mA PNP Transistor
Others parts
BZ1—-Piezo speaker___1 pcs.
Battery 1.5 volts with battery holder AA 1.5Vx2
Solid wire.


  1. Chirantan Kansara February 13, 2015 Reply
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