Picture Number 1.

Heart of the Project is an LM393 Dual comparator.  Data Sheet is attached. It operates from +1 volt to +18 volt Single Supply Voltage Range. Negative Supply Voltage is not necessary to use. 

What is the electrical resistance of water?

Resistivity in pure water is around 20, 000 000 ohm.

This is Water Probe that Senses the Water resistance. Look at the picture given below. Inside there is a conductor to sense the conductivity of water in terms of resistance. Water-resistance means conductivity in water relates to in terms of resistance is near about 1  Mega Ohm. For different chemical liquids, resistance differs.

Picture Number 2

 Picture Number 3

Below there is a picture number 4, of water in a tumbler and Multi-meter Probes inserted into the water.

Picture Number 4

Meter Shows the Water conductivity in terms of Resistance is in the range of 100 Kilo Ohm to 1.8 Mega Ohm. as shown in Picture Number 5 and 6

Picture Number 5

Picture Number 6

To measure the conductivity in water in terms of resistance,  put the black probe in Common Slot and Red probe in V-Oham-mA Slot and keep the Multi-meter knob in Mega ohm Range.

At first 3 thresholds are set for Comparator.

There are three sets of to sense each level. Green LED Set, Yellow  LED Set, and Red LED Set.

In General, one set of circuits is shown in the above picture number 1.

Voltage divider network A is applied as shown in picture Number 1. 100-kilo ohm and 47 Kilo ohm

100 Kilo Ohm and 33 kilo Ohm and 100 Kilo ohm and 56 Kilo Ohm, Among 100-kilo ohm, is common.

Voltage Across Resistor 47 K, 33 k and 56 K is applied across Inverting terminal and voltage around

2.87 volts and 4.5 volts around 100 Kilo ohm Resistor.  

There is Voltage Divider network B is set by 1 Mega ohm and Water resistor that is 1  Mega Ohm and 300-kilo ohm. Actually Water resistance decreases from 1.8 Mega ohms to 100 Kilo and again rises towards 1 Mega. There is always variation in resistance. It is not constant and depends on the quality of water and at room temperature.

Now Analyse, Voltage across Inverting terminal is 2.43 volts because 56 k, 33 k, and 47 k comes in parallel.

When there is the Water condition

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Now when there is water, the voltage across Non-Inverting terminal is 50 % of 9 volts i.e. 4.5 volts So Switch over happens and  4.5 volts Greater than 2.87 volts and SO switch over happens and Output is High i.e. around 9 volts and LED Glows.  Current flowing through  LED is adjusted at about 10 mA.

No Water condition

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When there is no water, the voltage across the Non-Inverting terminal is zero >  2.43 volts is false, and LED does not glow, it is off.

select R1 of Voltage divider network B at 1 Mega or Less than 1 Mega in Value. Currently, I have Selected R5 at 1 Mega Ohm as shown in Picture Number 1. R6 is Water Resistor is around 1.8 Mega Ohm at 20 degrees centigrade.

So it is very important to design the halve of the Voltage divider network and care must be taken.

Water Level Indicator is not kept 24 hours On. At the instant to relay information make it Switch on and make it off after getting information.

Why I have designed 9 volt Power Source?

First Question we have to ask ourselves is that

How much voltage is required to glow a LED?

is the power supply voltage in volts, e.g. 9-volt battery. on LED datasheets. Typically, the forward voltage of an LED is between 1.8 and 3.3 volts. It varies by the color of the LED. The LED data Sheet is attached.
 

(When the water level is sensed there  is switch over by comparator  to indicate the water level and corresponding level information is received.)

LM393 is used as a Dual comparator. 10-kilo ohm is the pull resistor of the Comparator. 100 k, 33 k,47 k, 56 k voltage divider to set three thresholds.  1 Mega ohm is used to switch over the voltage level set by thresholds.

Below is Picture Number 7 is the Deployment file, In that there is a capacitor of 1uf connected across 1 Mega ohm Resistor to avoid the false change of logic levels.

There is essential to insert the Vcc probe and Ground Probe deep at the very Bottom water level to get the  Logic levels.

Picture Number 7

PICTURE NUMBER 8

Below is the PCB design of the above schematic which is designed in Eagle Cad.

Level Information indicated by  LEDs (Light Emitting Diode)

• Green LED --> Tank is Full 100 %
• Yellow LED--> 50 % full
• Red   LED ---> 25 % full
• All LEDs OFF --> No Water

PICTURE NUMBER 9

PICTURE NUMBER 10