Here is a simple project more useful in watering plants automatically without any human

interference. We may call it as Automatic plant irrigation system. We know that people do not pour
the water on to the plants in their gardens when they go to vacation or often forget to water plants.
As a result, there is a chance to get the plants damaged. This project is an excellent solution for
such kind of problems.
Block Diagram of Automatic Plant Irrigation System:

Explanation:
Circuit is not that much complicated. We use the basic concept in this circuit i.e. soil have high
resistance when it is dry and has very low resistance when it is wet.
By using this concept we will make the system work. We insert two probes in the soil in such a
way that that they will conduct when the soil is wet and they will not conduct when the soil is dry.
So, when the probes do not conduct, system will automatically detect this condition with the help
of HEX inverter which will become high when the input is low.
HEX inverter will trigger the NE555 Timer and this NE555 timer will trigger another NE555 which
is connected to the output of first NE555. Now the second NE555 which is configured as astable
multivibrator will help to switch on the Electric valve and as result, it will allow the water to flow to
the soil.
When the water wet the soil, probes will again conduct and make the output of 7404 low which
will make the first NE555 to low and also drive remaining circuit to low. So, automatically it will
switch off the valve.
Main Components in Automatic Plant Irrigation System:
Hex Inverter 7404: the main function of the inverter is to give the complemented output for its input
i.e. it will give output which is opposite to input. For example, if the input is low to the inverter, then
the output will be high. Just like the normal inverter which gives high output when the input is low
and gives low output when the input is high. 7404 IC will be having six independent inverters;
Operating supply voltage is around 4.75V minimum to 5.5V maximum, normal supply voltage is 5V.
They are used in different applications like inverting buffers, drivers, hex inverters etc. 7404 IC will
be available in different packages like DIP (dual inline package), QFP (Quad Flat Package) etc. The
pin configuration of Hex Inverter 7404 is shown below.

Circuit Diagram of Automatic Plant Irrigation
System:

Circuit Explanation:
We are all well aware that the plants will die due to lack of water in the soil. Soil will have high
resistance when it is dry and it will have very low resistance when soil is wet. We use this simple
logic to water the plants and make the circuit work.
Two probes which are connected to the circuit are placed into the soil. The two probes will
conduct only when soil is wet (resistance is low) and they cannot conduct when soil is dry due to
high resistance. The voltage is given to the probes to conduct is given from the battery connected
to the circuit.
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 is triggered at pin 2, it will generate the output at pin 3 which is given to the
input of second NE555 timer. The second 555 timer is configured as astable multivibrator which
got triggered by the first 555 timer and will generate the output and drive the relay which is
connected to the electrically operated value through the transistor SK100. You can use a heat
sink for SK100 transistor if it is dissipating more heat.
The output of second NE555 timer will switch on the transistor SK100 which will drive the relay.
Relay which is connected to the input of electrical value and output of value is given to the plant
plots through the pipe.
When transistor has turned on relay, it will open the valve and water is poured on to the plants
pot. When the water content in the soil is increased, the resistance in the soil will get decreased
and conduction of the probes will get started which will make the 7404 Inverter to stop the
triggering of first 555 timer. Ultimately it will stop the electrical valve which is connected to the
relay. Variable resistor (R5) and capacitor (C1) are used to adjust the valve when to we want to
conduct the probes.
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
Note:
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.





This stress monitor lets you assess your emotional pain. If the stress is very high, it gives
visual indication through a light-emitting diode (LED) display along with a warning beep.
The gadget is small enough to be worn around the wrist.



Fig. 1: Circuit of the stress meter

The gadget is based on the principle that the resistance of the skin varies in accordance
with your emotional states. If the stress level is high the skin offers less resistance, and if
the body is relaxed the skin resistance is high. The low resistance of the skin during high
stress is due to an increase in the blood supply to the skin. This increases the permeability
of the skin and hence the conductivity for electric current.

This property of the skin is used here to measure the stress level. The touch pads of the
stress meter sense he voltage variations across the touch pads and convey the same to the
circuit. The circuit is very sensitive and detects even a minute voltage variation across the
touch pads.

The circuit comprises signal amplifier and analogue display sections. Voltage variations from
the sensing pads are amplified by transistor BC548 (T1), which is configured as a common-
emitter amplifier. The base of T1 is connected to one of the touch pads through resistor R1
and to the ground rail through potmeter VR1. By varying VR1, the sensitivity of T1 can be
adjusted to the desired level. Diode D1 maintains proper biasing of T1 and capacitor C1
keeps the voltage from the emitter of T1 steady.

The amplified signal from transistor T1 is given to the input of IC LM3915 (IC1) through
VR2. IC LM3915 is a monolithic integrated circuit that senses analogue voltage levels at its
pin 5 and displays them through LEDs providing a logarithmic analogue display. It can drive
up to ten LEDs one by one in the dot/bar mode for each increment of 125 mV in the
input.Here, weve used only five LEDs connected at pins 14 through 18 of IC1. LED1 glows
when input pin 5 of IC1 receives 150 mV. LED5 glows when the voltage rises to 650 mV and
LED5 flashes and piezobuzzer PZ1 beeps when the stress level is high.


Fig. 2: Display panel

Resistors R4 and R5 and capacitor C2 form the flashing elements. Resistor R3 maintains the
LED current at around 20 mA. Capacitor C3 should be placed close to pin 3 for proper
functioning of the IC. Zener diode ZD1 in series with resistor R6 provides regulated 5V to
the circuit.

The circuit can be assembled on a small piece of perforated board. Use transparent 3mm
LEDs and a small piezobuzzer for audio-visual indications. Enclose the circuit in a small
plastic case with touch pads on the back side. Two self-locking straps can be used to tie the
unit around your wrist.


Fig. 3: Self-locking straps
After tying the unit around your wrist (with touch pads in contact with the skin), slowly vary
VR1 until LED1 glows (assuming that you are in relaxed state). Adjust VR2 if the sensitivity
of IC1 is very high. The gadget is now ready for use.