Specifications
CIRCUIT IDEAS
G.S. SAGOO
T
his digital water level meter shows
up to 65 discrete water levels in
the overhead tank (OHT). This
helps to know the quantity of water in
the OHT quite precisely. The
circuit is specially suited for
use in apartments, hostels,
hotels, etc, where many taps
are connected to one OHT.
In such cases, if someone for-
gets to close the tap, this cir-
cuit would alert the opera-
tor well in time.
Normally, for multi wa-
ter level readings, one has to
use complicated circuits em-
ploying multi-core wires from
the OHT to the circuit. This
circuit does away with such
an arrangement and uses
just a 2-core cable to monitor
various water levels. Fig. 2.
shows various water levels
and the corresponding read-
ings on 7-sement displays.
IC1 and IC2 shown in Fig.
1 are CD4033 (decade up
counter cum 7-segment de-
coder) which form a two-digit
frequency counter. The CK
pin 1 and CE pin 2 of IC1 are
used in such a way that the
counter advances when pin 1
is held high and pin 2 under-
goes a high-to-low transition.
For water level reading,
which is applied to pin 1 of IC1. It com-
prises a positive pulse of variable dura-
tion (0.5 second to 3 seconds, depending
upon the water level in the tank) followed
by 4-second low level.
Thus, during positive duration of tim-
ing pulse at pin 1 of IC1, the frequency
counter is allowed to count the number of
negative going pulses which are continu-
ously available at its pin 2. At the same
time the pnp transistor T1 remains cut-off
due to the positive voltage at its base, and
this frequency counter needs two types of
inputs. One of the these is a continuous
30Hz clock (approx.), which is applied to
pin 2 of IC1. The other is a timing pulse,
DIGITAL WATER LEVEL METER
K. UDHAYA KUMARAN, VU3GTH
power supply, the supply to the trans-
former is not available and the relay de-
energises. Thus, once the supply is inter-
rupted even for a brief period, the relay is
de-energised and you have to press switch
S1 momentarily (when the supply re-
sumes) to make it available to the load.
Very-short-duration (say, 1 to 5 milli-
seconds) interruptions or fluctuations will
not affect the circuit because of presence
of large-value capacitor which has to dis-
charge via the relay coil. Thus the circuit
provides suitable safety against erratic
power supply conditions.
Fig. 1
36