Automatic Plant Watering System, Ready Kit, 100% Tested


Automatic Plant Watering System circuit is presented here is based on the readily available moisture sensor, comparator IC LM393 and relay. The moisture sensor is used as soil moisture detector while IC LM393 used as comparator. In the absence of water, no moisture sense in the soil. As a result moisture sensor start conducting and turn ON the water pump. However, when there is a moisture present in the soil the moisture sensor detect moisture and water pump stays off.

Buy Online “Automatic Plant Watering System” Ready Kit, 100% Tested from below and get fastest delivery in India

Complete working video can be seen from

Follow us on Instagram

Application of the circuit:

Most of the moisture sensor based circuits available in market use one or another kind of soil moisture detector probe which increases the cost and also require complicated circuitry around it. But this moisture sensor based circuit uses readily available soil moisture detector probe as moisture detector. The functioning of this Automatic Plant Watering System circuit is to detect moisture in soil and automatically activate the water pump in absence of moisture. Water pump is ON continuously indicating the absence of moisture till it detects moisture on moisture sensor.

Why this particular circuit:

Soil moisture detector probe used here as a moisture detector. The variation in moisture wanted can be easily done by introducing water. The circuit operates normally over a DC voltage of 5V which can be obtained by DC supply cable.

Explained working of circuit:

The basic idea behind the circuit operation is to turn ON water pump in absence of moisture. The soil moisture detector probe is needed for this purpose. Soil moisture detector probe is a device that converts soil moisture to electric energy. Here, Automatic Plant Watering System circuit works as moisture detector while soil moisture detector probe working as moisture sensor that turns ON water pump. IC LM393 is used as comparator. Soil moisture detector probe output is connected as input to comparator.  Pin no. 4 of LM393 is pulled towards ground. Relay is used as a switch. When relay is activated, normally closed contact becomes open and normally open contact becomes closed. In normal condition, there is moisture in the soil and water pump stays off. Now consider second scenario when there is no moisture in the soil, the water pump turns ON.

How to build:

First of all read the given manual thoroughly and study the circuit given in the figure. Also have look at PCB and components supplied along with the kit. Each component has to be soldered in its position on PCB.

Identification of resistors is done by color coding. The color band on each resistor corresponds to its exact value.

There are different methods in which values are defined on capacitors. But usually values are specified numerically on them.

Can you make out the whole working of circuit and are you able to identify each component separately as to where each of them has to be placed?

If yes only then proceed further to actually mounting and soldering the parts.

Not ICs but their sockets are to be soldered on PCB. This is to make mounting and dismounting of ICs easy while troubleshooting.

Start from left most corner of PCB and solder the components one by one on their correct position on PCB.

Before soldering any component see that you have placed it at its right position and with correct polarity. Give due attention to diodes and electrolytic capacitors as they are polarity dependent.

Do the soldering of other components in the same way while keeping in mind that components with long and sensitive leads like capacitors and transistors are soldered last.

Testing the kit:

After assembling and soldering of components on PCB, connect external DC power source of 5V.

For testing purpose manually induce water in the soil. Pump turns on in absence of water.

Now set the desired intensity at which you want detection of light. This can be done by changing the resistive value of R2 variable resistor.

Install the unit in soil.

ICs used here:

The only IC used here is LM393

It is dual differential comparator IC.

This 8 pin IC is popular and commonly used IC

Part List


U1               – LM393

Base            – 8 pin

Resistors(all ¼ watt +/-5% carbon unless stated otherwise)

R2               – 10k Ohm(variable)

R3               – 1k Ohm

R4               – 1k Ohm

R5               – 10k Ohm

R6               – 10k Ohm

Capacitor C1               – 1uF


D4:              – moisture sensor


D1:              – Red LED

D2:              – Green LED

5 V USB Cable