Automatic Water level controller using IC 555

A simple circuit for Automatic Water level controller

Ok, what this circuit will do??

As the title suggested this circuit will control the level of water in a tank, suppose a water motor is used to fill a water tank, then normally what we do??,, we turn ON motor and wait for tank to fill and when the tank gets full then we turn OFF motor, and again when tank gets empty we turn ON the motor and again wait for tank to get full and so on…. same thing can be done by this little circuit. When water level in the tank goes low, then the circuit will turn ON motor and when the tank gets full this circuit will turn OFF motor.

we can see in the above diagram that three sensor wires from the circuit are going inside the water tank and an AC water motor is connected to the relay switch of the circuit,
Now when water level will go below the low-level sensor; circuit will turn ON the relay switch, as a result, the connected motor will also get turned ON and when the water level reaches the high-level sensor the connected motor will turn OFF.

Working

This Automatic Water level controller circuit is based around a timer IC 555,

When water level goes below the low-level sensor, the voltage at pin 6 of IC555 goes low which SET the internal SR Flip Flop of IC 555 and output at pin 3 of IC555 goes high which turns ON the transistor and relay, causing the connected motor to turn ON. afterward, when the water level reaches and touches the high-level sensor, the voltage at pin 3 of IC555 goes high which RESET the internal Flip Flop of the IC and output of IC555 goes low, as a result, the connected motor turn OFF.

Components Required

Let’s see what components we need for this Automatic Water Level Controller Circuit.

1)Resistors
2.2K -(2)
10K -(3)
1M -(2)
2)Transistor
2N2222 -(1)
3)IC
555 -(1)
4)Capacitor
0.01uF -(1)
[code for this capacitor is 103]
5)Diode
1N4007 -(1)
6)Relay 12V
7)Zero PCB/Prototype PCB/DOT PCB
8) IC Base 8Pin

About Sensor
Any metal rod or any small metal plate connected at the end of the wire can be used as sensor for this project.

Ok that’s it, now you can build this project””

Want to know more……….

Let’s try to understand how this circuit is working, what’s going on
before going further we need to know few other things such as Comparator, Internal structure of IC 555, SR Flip Flop and voltage divider ;; at least basic structure and working principle of these things

Internal structure of IC 555


Just have a look at the internal structure of IC 555
as we can see it is made up of two Comparators, one SR Flip Flop, Inverter, Transistor, and few resistors.


now we will look at them separately one by one, we will not go through deeper analysis but just basic structure or working of them..

COMPARATOR



COMPARATOR

Above is a symbolical representation of Comparator, It has two analog inputs terminals inverting(-V) and non-inverting(+V) and one digital output terminal Vout, other two terminals noted as +Vcc and -Vcc are used to give power to the Comparator.
At the digital-output terminal output will be either 0 or 1 based upon the inputs.
A COMPARATOR compares the voltage present at its two input terminals and gives output according to it;
If the voltage at non-inverting(V+) terminal is higher than the voltage at the inverting(V-) terminal then Comparator will give output “1”
and
If the voltage at inverting terminal(V-) is higher than the non-inverting terminal(V+) then Comparator will give output “0”

If V+ > V- , then Vout= 1
and
If V- < V+ , then Vout= 0

Usually in practical use, one of the input terminal (V+ or V-) is connected to a fixed voltage which we call Vref or reference voltage, so a variable voltage at another terminal determines the output of Comparator:-
For Example:- If we connect a fixed voltage( Vref ) of 5v at ‘V+’ terminal of Comparator then;
the output will be logic 1, If the voltage at ‘V-‘ terminal is less than 5v
and
the output will be logic 0, If the voltage at ‘V-‘ terminal is higher than 5v.

SR Flip Flop

as we have decided we will not go into deeper analysis. Above we can see two images one is SR Flip Flop and the other is it’s ‘Truth Table’, S and R are the two inputs of Flip Flop and Q and Q bar represent its output. Q bar is actually complement of Q, If Q is 1 then Qbar will be 0 and If Q is 0 Qbar will be 1 .
The truth table represents the output characteristics of the SR Flip Flop. i.e. what output we will get at Q and Qbar when 0 or 1 is applied to the S and R inputs.

VOLTAGE DIVIDER

Just have a look at the above diagram, we can see that two resistors in series are connected to a Battery or a Power supply. Now assume we are using a 12v Battery or a 12v Power supply then what will be the voltage reading at point X w.r.t to point Z, i.e. if we set our multimeter to DC voltage reading mode and connect the probes of multimeter to point X and point Z, then what reading we will get in our multimeter,, it will display voltage of the battery or the connected power supply, as point X and Y are directly going to the battery.
Now, what if we measure the voltage at point Y and point Z, we will get a new voltage reading that will be less than the previous voltage reading,,,, why and how much less?? ” ” Here comes the Ohm’s Law””
There will be some amount of voltage drop across R1 and we are measuring voltage after R1 w.r.t Gnd.
The amount of voltage that will drop across R1 will depend upon the value of R1 and the amount of current flowing across it. If the value of resistor R1 is ‘ R ohms’ and the value of current flowing through it is ‘ I ampere ‘ then the voltage drop across R1 will be ‘ V=IR ‘ this is Ohm’s Law, .
So the point is; by implementing suitable values for resistors in a voltage divider network we can get the desired voltage at a point or we can say that we can divide the voltage into two or more parts using a voltage divider network.

Above is an example of a voltage divider network using three resistors ;
Let us assume +Vcc= 12V and value of R1=5K, R2= 5K, and R3= 5K.
We can see that all three resistors are in series so equivalent resistor(total resistor value between A and Z) will be ‘R1+R2+R3’ i.e. 5K+5K+5K=15K ; so we can say that there is a 15K resistor connected between +Vcc and Gnd. or there’s a 15K resistor connected to a 12V source. now we have V=12 and R=15 Kilohms, so by using Ohm’s law, we can find out how much current is flowing through 15K resistor( or R1, R2, and R3).
V=IR ; where V is the voltage, I is the Current, R is the Resistor[This is Ohm’s Law].

so, 12= I x (15 x 1000)
or I= 12/(15 x 1000)= 4/5000;
or I= 0.0008 Amps.

If the resistors are connected in series then the same amount of current flows across all the resistors, therefore in the above example, 0.0008 Amp of current is flowing through R1, R2, and R3.

Now come to the question

What will be the voltage between point A and point Z ?
Obviously, it will be the voltage of the battery or Power supply i.e. 12v.
What will be the voltage at point B and point Z ?
Here we are measuring the voltage between point B and Gnd(Gnd. or 0). If we start from +Vcc side then point B comes after Resistor R1 and there will be some amount of voltage drop across R1,,,, but how much??
Let’s see. we know that the value of R1 is 5 Kilohms and 0.0008 Amp of current is flowing through it, so voltage drop across this resistor will be V=IR , i.e.
V=0.0008 x (5 x 1000)
or V= 4 volts.
So, when we measure voltage between point B and Gnd. we will get;
12V – 4V = 8 V

Let’s move to another question

What will be the voltage between point C and point Z ?
Here we are measuring the voltage between point C and Gnd. In the diagram, we can see that there are two resistors before point C, and there will be a voltage across both of these resistors. we have already calculated the voltage drop across R1, now we will see voltage drop across resistor R2;
The value of R2 is 5 Kilohms and I= 0.0008 Amps.
so voltage drop across this resistor will be V=IR , i.e.
V=0.0008 x (5 x 1000)
or V= 4 volts.
Total voltage drop due to R1 and R2 will be 4V + 4V= 8V. [4V across R1 and 4V across R2]
So, when we measure the voltage between point C and Gnd. we will get;
12V – 8V = 4 V .

If you are good at mathematics then you will easily realize that;
the voltage at point B will always be 2/3 of Vcc and
voltage at point C will always be 1/3 of Vcc.


Now scroll up this page and once again look at the Internal structure of IC 555, you will see a similar voltage divider network that we have discussed, you can also see that upper comparator is getting a fixed reference voltage Vref at V- terminal which is 2/3 of Vcc and the V+ terminal of Lower comparator is connected to a fixed reference voltage Vref which is 1/3 of Vcc.
So,
If voltage at Pin 6 of IC 555 is greater than 2/3 Vcc then the output of upper comparator will be logic 1 .
and
If voltage at Pin 6 of IC 555 is less than 2/3 Vcc then the output of upper comparator will be logic 0 .
also;
If voltage at Pin 2 of IC 555 is greater than 1/3 Vcc then the output of lower comparator will be logic 0 .
and
If voltage at Pin 6 of IC 555 is less than 1/3 Vcc then the output of upper comparator will be logic 1 .


So far we have seen SR Flip Flop and its Truth table, Basic working of Comparator, Voltage Divider and internal structure of IC 555.

Now come back to our original circuit i.e. circuit of Automatic water Level controller using IC 555

In the above circuit diagram, we can see two more voltage divider ……,,,,, where ??,
Ok let’s see one of them, look at R1 and R2, we can see that one end of R2 is connected to Gnd. and one end of R1 is going inside the water tank; also one of the sensors inside water tank is directly connected to the +Vcc, so we can say that one end of R2 is connected to +Vcc through water or resistance of water,
resistance of water ,,,,,….

When tank is full or when water is touching the high-level sensor then the water present between the high-level sensor and the Lowermost sensor( sensor connected to +Vcc) will act as Resistor, the value of this water resistor will depend on the conductivity of water. [Refering above Figure]

Water containing more minerals or particles will be more conductive thus the value of water-resistor will be less, and If water is less conductive then the value of water resistor will be high.

The Point is to get a voltage greater than “2/3 of Vcc” at Pin-6 of IC555 when water touches the high-level sensor and to get voltage higher than “1/3 of Vcc ” at Pin-2 of IC555 when water is touching Low-Level sensor. We can easily achieve these values if we are using normal tap water or underground water, because the resistance of normal Tap water or underground water lies usually between 40kilohms to 200kilohms.

Now we will see the working of Automatic water level controller in Steps:-
Stage-I
Condition:- Tank is empty or water in the tank is below low-level sensor.

In this condition, we can see that one end of both R1 and R3 is going nowhere( wires from these resistors are going to the high and low sensors which are just hanging in the air inside water tank.)
So, Pin6 is only connected to Gnd through R2, and Pin2 is only connected Gnd through R4.

Input and output conditions Comparator
Upper comparator:-
The voltage at Pin6 is less than 2/3 of Vcc.
i.e. the voltage at +V terminal of the comparator is less than voltage at -V terminal of comparator;
i.e. In the upper comparator,
+V < -V ; so the output of upper comparator will be ‘ 0 ‘

Similarly in Lower comparator,
The voltage at Pin2 is less than 1/3 of Vcc.
i.e. the voltage at -V terminal of the comparator is less than voltage at +V terminal of comparator;
i.e. In the Lower comparator,
+V > -V ; so the output of Lower comparator will be ‘ 1 ‘

Output of these comparators goes to the Inputs of SR Flip-Flop;
the output of Upper comparator goes to the input R of SR Flip-Flop and output of the Lower comparator goes to the input S of SR Flip-Flop.

So at this stage inputs of SR Flip-Flops are;
S = 1
R = 0.
Looking at truth-table of SR Flip-Flop we can say that when S=1 and R=0 then,
Q = 1, and
Q bar = 0

The Qbar of SR FlipFlop is connected to the input of the OUTPUT STAGE of IC555, as shown in the diagram of the Internal structure of IC 555.
This Output Stage also act as an INVERTER i.e. it will also invert its input or we can say that If the input of this OUTPUT STAGE is 0 then its output will be 1 and when input of OUTPUT STAGE is 1 then its output will be 0. and output of this OUTPUT STAGE goes to the Pin3 of IC555 which is also known as the output Pin of IC555, so output of this OUTPUT STAGE will be the OUTPUT of IC 555.
In this stage, we have Qbar= 0. so output of IC555 will be ‘1’ or we can say that the output of IC555 is HIGH.

The output Pin i.e. Pin3 of IC555 is connected to the base of NPN Transistor and there’s a resistor in between them. this resistor is used to limit the base current of transistor.

When output of IC555 goes High it provides base current for transistor which turn ON the transistor and this transistor is driving the relay so Relay turns ON, as a result, the connected motor also gets turned ON.
[When output of IC555 will be high- AC Motor will turn ON, and when output of IC555 is LOW then AC Motor will be OFF]

In this Stage when water is below Low-level sensor, we have:-
S = 1, R = 0, Qbar = 0, and
Output of IC555 = 1(or HIGH)
AC Motor = ON

STAGE 2

In the previous Stage, motor gets ON and started to fill the water tank; now when water touches the Low-level sensor.

Condition:- When water is touching Low-level sensor
or
Water is above Low-level sensor and below High-level sensor

In this condition, PIn2 is getting voltage higher than 1/3 of Vcc.

In UPPER COMPARATOR we have:-
voltage at Pin6 is less than 2/3 of Vcc.
i.e. the voltage at +V terminal of the comparator is less than voltage at -V terminal of comparator;
i.e. In the upper comparator,
+V < -V ; so the output of upper comparator will be ‘ 0 ‘

at Lower comparator,
The voltage at Pin2 is higher than 1/3 of Vcc.
i.e. the voltage at +V terminal of the comparator is less than voltage at -V terminal of comparator;
i.e. In the Lower comparator,
+V < -V ; so the output of Lower comparator will be ‘ 0 ‘

So at this stage inputs of SR Flip-Flops are;
S = 0
R = 0.
Looking at truth-table of SR Flip-Flop we can say that when S=0 and R=0 then,
Q = Qbar = NO CHANGE {it will be in previous state}
In previous Stage, we have; Q= 1 and Qbar = 0,
In this stage also we will get the same value of Q and Qbar as Q and Qbar will not change. so in this stage we will get same output i.e. output of IC555 will be HIGH and Motor will remain ON

SUMMARY

In this Stage, When water is touching Low-level sensor
or
Water is above Low-level sensor and below High-level sensor then we have:-

S = 0, R = 0, Qbar = NO CHANGE i.e. Qbar= 0, and
Output of IC555 = 1(or HIGH)
AC Motor = ON

STAGE III

In previous stages the Motor is ON and filling the water tank, after some time the level of water in tank will rise and reach the high level sensor.

Condition:- When water touches the High Level Sensor.

In this condition Pin6 of IC555 will be receiving voltage higher than “2/3 of Vcc.” and
Pin2 will be getting voltage higher than “1/3 of Vcc.”

So, In upper Comparator we have:-
voltage at Pin6 is higher than 2/3 of Vcc.
i.e. the voltage at -V terminal of the comparator is less than voltage at +V terminal of comparator;
i.e. In the upper comparator,
+V > -V ; so the output of upper comparator will be ‘ 1 ‘

at Lower comparator,
The voltage at Pin2 is higher than 1/3 of Vcc.
i.e. the voltage at +V terminal of the comparator is less than voltage at -V terminal of comparator;
i.e. In the Lower comparator,
+V < -V ; so the output of Lower comparator will be ‘ 0 ‘

So at this stage inputs of SR Flip-Flops are;
S = 0
R = 1.
Looking at truth-table of SR Flip-Flop we can say that when S=0 and R=1 then,
Q = 0, and
Q bar = 1.

so output at Pin3 of IC 555 will be 0 or LOW. i.e. Motor will turn OFF.

SUMMARY
In this Stage when water is touching High-Level sensor, we have:-
S = 0, R = 1, Q= 0, Qbar = 1, and
Output of IC555 = 0(or LOW )
AC Motor = OFF

STAGE- IV

In the previous stage water tank get full and Motor get turned OFF; now when tank water is being used and the water level goes below the High-Level Sensor.

Condition:- When water level goes below the High-Level Sensor.
or
Water level is below the High-Level Sensor and above the Low-level sensor.

In this condition, PIn2 is getting voltage higher than 1/3 of Vcc.

In UPPER COMPARATOR we have:-
voltage at Pin6 is less than 2/3 of Vcc.
i.e. the voltage at +V terminal of the comparator is less than voltage at -V terminal of comparator;
i.e. In the upper comparator,
+V < -V ; so the output of upper comparator will be ‘ 0 ‘

at Lower comparator,
The voltage at Pin2 is higher than 1/3 of Vcc.
i.e. the voltage at +V terminal of the comparator is less than voltage at -V terminal of comparator;
i.e. In the Lower comparator,
+V < -V ; so the output of Lower comparator will be ‘ 0 ‘

So at this stage inputs of SR Flip-Flops are;
S = 0
R = 0.
Looking at truth-table of SR Flip-Flop we can say that when S=0 and R=0 then,
Q = Qbar = NO CHANGE {it will be in previous state}
In previous Stage, we have; Q= 0 and Qbar = 1,
In this stage also we will get the same value of Q and Qbar as Q and Qbar will not change. so in this stage we will get same output as previous stage output i.e. output of IC555 will be LOW and Motor will remain OFF.

SUMMARY

In this Stage, When water level goes below the High-Level Sensor.
or
Water level is below the High-Level Sensor and above the Low-level sensor

S = 0, R = 0, Qbar = NO CHANGE i.e. Qbar= 1, and
Output of IC555 = 0(or LOW)
AC Motor = OFF.

STAGE – V

In previous stage, motor is OFF and suppose if water is being used or water from tank is drained then after some time level of water in the tank will go below the Low level Sensor.

Condition:- Water level is below Low-level sensor.

This condition is same as in the first stage; Lets see;

In this condition, we can see that one end of both R1 and R3 is going nowhere( wires from these resistors are going to the high and low sensors which are just hanging in the air inside water tank.)
So, Pin6 is only connected to Gnd through R2, and Pin2 is only connected Gnd through R4.

Upper comparator:-
The voltage at Pin6 is less than 2/3 of Vcc.
i.e. the voltage at +V terminal of the comparator is less than voltage at -V terminal of comparator;
i.e. In the upper comparator,
+V < -V ; so the output of upper comparator will be ‘ 0 ‘

Similarly in Lower comparator,
The voltage at Pin2 is less than 1/3 of Vcc.
i.e. the voltage at -V terminal of the comparator is less than voltage at +V terminal of comparator;
i.e. In the Lower comparator,
+V > -V ; so the output of Lower comparator will be ‘ 1 ‘

So at this stage inputs of SR Flip-Flops are;
S = 1
R = 0.
From Truth Table when S=1 and R=0 then,
Q = 1, and
Q bar = 0

In this stage, we have Qbar= 0. so output of IC555 will be ‘1’ or HIGH.
and once again Motor will turn ON.

So again motor will turn ON and this process will repeat and continue.

95 thoughts on “Automatic Water level controller using IC 555”

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