555 timer ic

Automatic Plant Irrigation System

This project will automatically water plants without the need for human intervention. It’s referred to as Automatic Plant Irrigation System. We know that when people go on vacation, they do not water their gardens and that they frequently forget to water them. As a result, there’s a danger the plants will be harmed. This project is a fantastic solution to situations of this nature.


  • Block Diagram of Automatic Plant Irrigation System:
    • Main Components in Automatic Plant Irrigation System:
  • Circuit Diagram of Automatic Plant Irrigation System:

Block Diagram of Automatic Plant Irrigation System:

Block Diagram of Electronic Plant Watering System


  • The circuit is not overly complicated. In this circuit, we apply the basic principle that dirt has a high resistance while dry and a very low resistance when wet.
  • We will make the system work by employing this concept. Two probes are inserted into the soil in such a way that they conduct when the soil is wet and do not conduct when the soil is dry. As a result, if the probes do not conduct, the system will detect this condition automatically using a HEX inverter, which will become high when the input is low.
  • The HEX inverter will activate the NE555 Timer, which will then activate another NE555 linked to the first NE555’s output. The second NE555, which is designed as an astable multivibrator, will now assist in turning on the Electric valve, allowing water to flow to the soil.
  • When water wets the soil, the probes conduct again, lowering the output of the 7404, which drives the first NE555 to low and the rest of the circuit to low. As a result, the valve will be turned off automatically.

Main Components in Automatic Plant Irrigation System:

Hex Inverter 7404: The inverter’s principal job is to provide complemented output for its input, i.e. output that is the polar opposite of the input. For example, if the inverter’s input is low, the output will be high. Similar to a standard inverter, which produces a high output when the input is low and a low output when the input is high. The 7404 IC will have six separate inverters; the operating supply voltage will range from 4.75V to 5.5V, with a standard supply value of 5V. They’re employed in a variety of applications, including inverting buffers, drivers, and hex inverters, among others. The 7404 IC will come in a variety of packages, including DIP (dual inline package), QFP (quad flat package), and others.

Inverter Pin Configuration

Circuit Diagram of Automatic Plant Irrigation System:

Automatic Plant Irrigation System

Circuit Explanation:

  • We’re all aware that plants will perish if there isn’t enough water in the soil. When the earth is dry, it has a high resistance, and when it is moist, it has a very low resistance. To water the plants and make the circuit operate, we use this simple logic.
  • Two probes are inserted into the soil and connected to the circuit. The two probes will only conduct when the soil is wet (low resistance) and will not conduct when the soil is dry (high resistance). The battery connected to the circuit provides the voltage for the probes to conduct.
  • When the soil is dry it will produce large voltage drop due to high resistance. This is sensed by 7404 hex inverter and makes the first NE555 timer trigger which is configured as monostable multivibrator with the help of a electrical signal.
  • When the first NE555 timer is activated at pin 2, it generates an output at pin 3 that is fed into the second NE555 timer’s input. The second 555 timer is set up as an astable multivibrator that is activated by the first 555 timer. It generates an output and drives a relay that is connected to the electrically operated value via the transistor SK100. If the SK100 transistor is dissipating too much heat, a heat sink can be used.
  • The second NE555 timer’s output will activate the transistor SK100, which will control the relay. The plant plots are fed through the pipe by a relay that is coupled to the input of electrical value and output of value.
  • When the transistor activates the relay, the valve is opened, and water is pumped into the plant pot. When the water content in the soil increases, the resistance in the soil decreases and probe conduction begins, causing the 7404 Inverter to halt the first 555 timer from being triggered. It will eventually shut down the electrical valve that is attached to the relay. When we want to conduct the probes, we modify the valve using a variable resistor (R5) and a capacitor (C1).
  • The capacitor C5 (0.01uf) is used to ground, the CV pin of second NE555 timer. C3 will remove the AC noise and allow only DC to the remaining circuit. C4 and R3 will constitute to configure the NE555 in astable multivibrator.

Values of the Components in the Circuit:

  • Capacitor (C4) = 10u 16V.
  • Capacitor (C5) = 0.01u.
  • Resistor (R3) = 27K
  • Resistor (R4) = 27K
  • Diode (D1 and D2) = IN4148
  • Relay = 6V, 150 ohms


  • Battery should be continuously monitored from power outage or simply you can use 9V DC supply adaptor.
  • Probes must be inserted into the soil. They should not be kept on the soil.
  • Electric valve should be used for best result.


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