This device is designed to indicate the level of water in the underground tank and produces the sound when the sensor detects the presence of a water at different levels. This enables the occupant of the house to take the necessary precautions to eliminate the wasting of water .

3. All the LEDs (LED1, LED2, LED3 and LED4) are lit, except LED5. Each LED
indicates the corresponding level of water in the underground tank. The water
level indicator is also used in swimming-pool, factories, and hotels.
This device is designed to
indicate the level of water in the
underground tank and produces the
sound when the sensor detects the
presence of a water at different levels.
This enables the occupant of the house
to take the necessary precautions to
eliminate the wasting of water .
The different levels are well indicated
from 1 to 4. Initially the tank is full of
water. All the LEDs (LED1, LED2,
LED3 and LED4) are lit, except LED5.
Each LED indicates The different levels
are well indicated from 1 to 4. Initially
the tank is full of water.

4. Now, when the water drops below level 1,
this means the tank is almost empty,
LED1 will turn off, LED5 will blinking and
an audible signal sounds and continue to
do so as long as the water level is below
level1. If this audio signal becomes
disturbing, BP1 should be briefly
depressed to silent it. Now, when the
underground tank is filled gradually with
water, LEDs, from 1 to 4 , go on also
gradually. working explanation of this
When the water drops below level 4,
the LED4 goes out and an audible
signal is emitted for a short period to
alert the user. Same thing, when the
water level drops to level 2 then 3, in
this case LED2 and then LED3 turn
off and a clear sound is also
produced.

5. Block diagram
Sensor
Presence of water
Lighting of LEDs one after an other
No water at level 4, 3, 2
LED1
LED2
LED 3
Alarm
switch off
No water at level 1
LED 4
LED5
Continueous
alam
switch off
flashing
Turn off alam

6. Water

7. Reference to the circuit diagram fig.1 shows that the unit is based on
transistors and integrated circuits IC1 and IC2, well known 555 timer. It
is powered with 9 volt DC supply. In this water-level controller circuit, the
common probes is +9V supply. The other sensing probes in underground
tank are marked 1, 2, 3 and 4. The low-level and high-level probes in the
underground tank are marked ‘4’ and ‘1’ respectively. The circuit is
based on the principle of electrical conductivity of water.
The main components have been configured as follow
 Transistors Tr1,Tr2,Tr3,Tr4,Tr5,Tr6 and T7 as switch;
 Transistors Tr8 and Tr9 as bistable circuit ;
 IC1 as monostable multivibrator (one shot),
 IC2 as standard astable multivibrator (oscillator)
f= 1.44/[ R21+2(R20+VR2) .C3] or f= 1.44/ [R21+2(R20) .C3]

8. Fig.1
Whole Diagram
of water level
indicator

9. The sensor consists of 4 copper conductors that are
located at equal distance from each other . Each copper is
equivalent of one level, i.e. copper 1 means level 1(tank is
almost empty) and copper 4 level 4 (tank is full). In addition
to that, there is a positive common probe. All coppers are
connected to the circuit by means of electrical wires
contained in a sealed plastic tub.
The circuit is based on 4 transistor switches. Each
transistor is switched on to drive the corresponding
LED , when its base is supplied with current through
the water through the electrode probes.
When the tank is full, some positive current passes
through water to the bases of the NPN transistors Tr1, Tr2
and Tr3. This turns on all these transistors and all LEDs
are glowing, except LED5 which is off for the time being.
No alarm is heard. They all remain in this state as long as
water makes a connection between positive supply rail and
the base of the transistors NPN Tr1, Tr2, Tr3, and Tr4. So to
conduct all these transistors’ base must be connected to the
positive supply around 0.6 V.
Probe

10. Furthermore, when water reaches each level (Level2, level3, level4) , a
positive pulse is sent from the collector of the transistor (Tr1, Tr2,Tr3,Tr4)
to the base of Tr7 through C1 and R15, the collector of Tr7 is now at
negative voltage and a negative pulse is applied to pin 2 of IC1 device in
standard monostable configuration through C1. The IC1 is triggered , pin 3 is
high and a sound is generated for few seconds to draw the occupant’s
attention. The output pin 3 goes go high and then it returns to a low level near
0 at the end of the cycle . The duration of the high is based on R13, RV1 and
C8. This duration can be altered by adjusting RV1 . Let's remember that
Tr7 and IC1 are common devices to level 1, 2 and 3. Here we have made a 555
astable monostable multi-vibrator for generating alarm signal as we already
mentioned. But in all three cases (Level 1,2,3), this monostable multi-vibrator
is controlled through Tr7 BC549.
Now, when the liquid level falls below level 4, Tr1 ceases to conduct. Its
collector voltage rises and becomes positive , then LED4 goes off. All the
remaining LEDs (LED3, LED2 and LED1) turn off when the water level is
below there corresponding level.

11. When the water drops below the position of probe 1, the Tr4 is in cut-off state. Its
collector become positive, both NPN transistors Tr5 and Tr6 get forward biased via
resistors R7/R9 and R7 R11 respectively. Hence, LED 5 flashes because its Tr6’s base is
controlled by a signal fed from the collector of TR4, also the positive voltage from the
emitter of Tr5 is applied to the circuit. The bistable circuit Tr8/Tr9 and IC2 are powered
by the positive voltage. Tr8 is biased by R17 and R18, while Tr9 is biased by R16 and
R19. The IC2, as an audio oscillator, generate an alarm, which means that the
underground tank is nearly empty.
The bistable circuit
(Tr8/Tr9) controls the
audio oscillator IC2
whose pin 4 must be
high in order to get
into action. Hence, the
output pin 3 becomes
high to activate the
buzzer and LED6 .

12. The bistable circuit is arranged so that it always triggers to the state that operate
the audio alarm when the water is below the level 1. It can be set to the alternative
state by operating push button switch BP1, and this switches the audio oscillator
off. C5 has the effect of delaying the build-up in voltage at Tr9’s base and Tr8
therefore conduct more heavily initially . The output of the bistable (Tr9’s
collector ) is initially in the high state, therefore the IC2 is activated because pin
4 is connected to the positive voltage and the oscillator will operated
continuously while the positive voltage is present. In other words, pin 4 of IC2 is
taken high to activate the oscillator, and low in order to mute it. By adjusting
RV2 it is possible to alter the frequency of the astable IC2 .

13. So the operating frequency of IC2 is a few Hertz which depends on the
timing components VR2, R20 and C4. It is between and 0.065 Hertz and
1Hertz. LED 5 flashes and the alarm will sound continuously as long as the
water level in the underground tank is below the level 1. The audio
oscillator can be silenced, if BP1 is briefly depressed, Tr8’s base is short
circuited to the negative supply rail.
When we start filing the tank , the water level touches first probe 1,
transistor Tr4 gets forward biased and starts conducting. This causes
reverse biasing of transistors Tr5 and Tr6 which get cut off. As a result,
Led5 is no longer blowing and the alarm is mute. As water level touches
probe 2, 3 and 4 the corresponding, Tr2, Tr3 and Tr4 will be turned on
again and the corresponding LEDs will be on.
Vr1 is being able to control the time duration of the monostable
multivibrator IC1. Vr2 adjusts the frequency of the astable multivibrator.

14. - PIN Diagram of IC1 and IC2 555
- Transistor BC549
- Buzzer
IC1 et IC2 NE555
Buzzer
All transistors
LED
Résistances
Condensateurs

15. The inside of the WLI

16. All LEDs are attached to the body of the appliance

18. Thankyou
University of Oum El Bouaghi , Algeria