Specifications

CONSTRUCTION
after taking appropriate remedial action
such as filling the foot-valve of the motor
with water or by removing the air-lock
inside the pipe.
Reservoir/sump tank level detec-
tion (Fig. 2). To start the motor when
the water level in the reservoir is suffi-
cient (level B), and to stop the motor when
the level falls below a particular level
(level A), are the two functions performed
by this section. IC6 (timer NE555) is con-
figured here to function in the bistable
mode of operation. When the water level
is below the minimum level A, both pins
2 and 6 of IC6 are low. In this state, the
output is high, as the internal R-S flip-
flop is in the set condition.
When water rises up to level A and
above, but below level B, pin 2 is at high
level. But in this state no change occurs
at the output because both the inputs to
the flip-flop are at logic zero, and so the
initial condition remains at the output.
When water touches level B probe,
pin 6 goes high and the output low. As a
result, collector of transistor T10 goes high
and the motor starts, if all other inputs
of IC7 are also high. Thus, water level in
the reservoir starts decreasing, and when
it goes below level A, the output of IC6
goes high and the motor stops.
Capacitors C20 and C21 act as filter
capacitors. The value of C21 is selected
such that it takes about 10 seconds to
reach 2/3 Vcc potential at pin 6, thereby
avoiding any erroneous start of the mo-
tor due to random fluctuations in the wa-
ter level of the reservoir due to any rea-
son. Resistors R22 and R23 are bleeder
resistors for discharging these capacitors.
Switches S3 and S4 are used to switch
‘on’ and switch ‘off’ the motor respectively,
in case of any emergency.
Miscellaneous functions (Figs 1
and 2). Transistors T3 through T5 are
used to drive LEDs D9 through D11, which
indicate the level of water inside the over-
head tank. The base of transistor T5 is
also connected to RESET pin 4 of IC9 to
sound an alarm (similar to that in case of
motor fault), indicating that the
overhead tank has been filled
completely. At this instant LED
D11 is lit to indicate this condi-
tion, while during motor fault
condition motor fault LED D27
is lit. Thus, by using the same
alarm facility and two different
LEDs, two different conditions
are indicated. The collector of the
same transistor T5 is connected to NAND
gate IC7 to switch off the motor when the
tank is filled up to its maximum level.
The ground pin of melody generator
UM66 (IC8) is connected to the emitter of
transistor T7. Thus, the melody IC is ‘on’
when the motor is running. The volume
of this melody can be controlled by preset
VR3.
Diode D23 connected across the relay
is the ‘snubber’ diode to protect emitter
junction of T7. Capacitor C25 is added to
avoid chattering of the relay.
LS1 can be any 0.25W-1W, 8-ohm
speaker. RL1 should be a good-quality
12V, 200-ohm relay, with a contact rating
of at least 10A. The combinations of ca-
pacitor-resistor C19-R21 and C27-R32
form power-on reset circuits. Since the
CMOS ICs are used here, the noise mar-
gin is quite high. The front-panel layout
for the system is given in Fig. 5.
Precautions
1. The probes should be made of a mate-
rial which is rust-proof, such as alu-
minium or brass.
2. Adjust presets VR1 and VR2 using
an auto-transformer.
3. IC1 and IC2 should be provided
with heat-sinks.
4. Level A of the reservoir should be
such that the foot-valve is just under wa-
ter.
5. The probes energised with AC (con-
nected to output of IC10) should run up
to the bottom of the OHT and sump tanks.
6. The water-flow-sensing probe
should be installed well above the ‘tank-
full’ level.
7. Remember that the ‘low level’ LED
indicates that water is between the ‘low
level’ and ‘half level’. When both ‘low level’
and ‘half level’ LEDs are on, the water
level is between ‘half’ and ‘full level’.
8. The probes inserted deep, down to
the bottom, should be completely uncov-
ered up to the top position of the tank,
and the different probes should be as close
PARTS LIST
Semiconductors:
IC1 - 7812, +12V regulator
IC2 - 7912, –12V regulator
IC3 - LM319 dual comparator
IC4 - CD4027 dual JK flip-flop
IC5 - CD4017 Johnson ring
counter
IC6, IC9 - NE555 timer
IC7 - CD4068, 8-input NAND gate
IC10 - µA741 op-amp
IC8 - UM66 melody generator
T1, T2, T7 - 2N2907 pnp switching
transistor
T3-T5,T8-T10 - 2N2222 npn switching
transistor
T6 - SL100 npn transistor
D1-D6, D23 - 1N4007 rectifier diode
D7-D11,
D27-D29 - LED, coloured
D12, D13,
D16-D21
D24-D26 - 1N4148 switching diode
D14,D15,D31 - 1N4001 rectifier diode
D22, D30 - 3.1V zener diode
Resistors (all ¼ watt, ±5% carbon film, unless
stated otherwise):
R1, R23 - 100-kilo-ohm
R2, R16 - 68-kilo-ohm
R3, R31 - 6.8-kilo-ohm
R4, R19, R20,
R24, R34,R35 - 2.7-kilo-ohm
R5, R7, R17,
R26-R28,R36 - 1-kilo-ohm
R6, R8, R30 - 560-ohm
R9-R11, R29,
R33 - 620-ohm
R12-R15, R21,
R25, R32 - 10-kilo-ohm
R18 - 270-kilo-ohm
R22 - 82-kilo-ohm
VR1-VR2 - 10-kilo-ohm, preset
VR3, VR4 - 4.7-kilo-ohm, preset
Capacitors:
C1-C4, C8, C10
C22- C24,
C28, C29 - 0.1µF ceramic disc
C5, C6 - 1000µF, 25V electrolytic
C7, C9, C13,
C16-C19, C21,
C26, C27 - 100µF, 25V electrolytic
C11, C12,C20 - 10µF, 25V electrolytic
C14 - 22µF, 25V electrolytic
C15,C25,C30 - 470µF, 25V electrolytic
Miscellaneous:
X1 - 230V AC to 15V-0-15V, 1A
sec. transformer
RL1 - Relay 12V, 200-ohm with con-
tact rating ≥ 10A
- IC bases
LS1 - Speaker, 8-ohm, 1W
- Heat-sinks for IC1 and IC2
S1 - Mains on/off switch
S2-S4 - Single-pole tactile switches
F1 - 0.5A fuse
F2-F3 - 1A fuse
- Sensing probes
Fig. 5: Proposed front-panel layout
as possible (but not too close to avoid any
water droplets sticking across them) to
have minimum water resistance.
A single-sided, actual-size PCB for the
complete circuit of the project is given in
Fig. 3, and a component layout for the
same is given in Fig. 4.
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