# 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 ΒΌ W + 5%
R1, R4——————–22K
R2, R3——————–220K
R5, R6, R8—————100K
R7————————-47K
R3————————-10M
Potentiometer
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.