04-12-2012, 06:07 PM
NUMERIC WATER-LE VEL IN DICATOR
Numeric Water Level Indicator.pdf (Size: 192.14 KB / Downloads: 58)
Most water-level indicators
for water tanks are based
upon the number of LEDs
that glow to indicate the corresponding
level of water in the container.
Here we present a digital version of the
water-level indicator. It uses a 7-segment
display to show the water level
in numeric form from ‘0’ to ‘9.’
The circuit works off 5V regulated
power supply. It is built around priority
encoder IC 74HC147 (IC1), BCD-to-
7-segment decoder IC CD4511 (IC2),
7-segment display LTS543 (DIS1) and a
few discrete components. Due to high
input impedance, IC1 senses water in
the container from its nine input terminals.
The inputs are connected to +5V
via 560-kilo-ohm resistors. The ground
Daniyal Syed
NUMERIC WATER-LE VEL IN DICATOR
s.c. dwivedi
terminal of the sensor must be kept at
the bottom of the container (tank). IC
74HC147 has nine active-low inputs
and converts the active input into active-
low BCD output. The input L-9
has the highest priority.
The outputs of IC1 (A, B, C and
D) are fed to IC2 via transistors T1
through T4. This logic inverter is used
to convert the active-low output of IC1
into active-high for IC2. The BCD code
received by IC2 is shown on 7-segment
display LTS543. Resistors R18
through R24 limit the current through
the display.
When the tank is empty, all the
inputs of IC1 remain high. As a result,
its output also remains high, making
all the inputs of IC2 low. Display
LTS543 at this stage shows ‘0,’ which
means the tank is empty. Similarly,
when the water level reaches L-1 position,
the display shows ‘1,’ and when
the water level reaches L-8 position,
the display shows ‘8.’ Finally, when
the tank is full, all the inputs of IC1
become low and its output goes low
to make all the inputs of IC2 high.
Display LTS543 now shows ‘9,’ which
means the tank is full.
Assemble the circuit on a general-
purpose PCB and enclose in a
box. Mount 7-segment LTS543 on the
front panel of the box. For sensors L-1
though L-9 and ground, use corrosionfree
conductive-metal (stainless-steel)
strips.