The Microcontroller based Water
Level Controller cum Motor Protector controls ‘on’ and ‘off’ conditions of the
motor depending upon the level of water in the over head tank (OHT), the status
of which is displayed on an LCD module. The circuit also protects the motor
from high voltages, low voltages, fluctuations of mains power and dry running.
The circuit of the Microcontroller
based Water Level Controller cum Motor Protector comprises of the operational
amplifier LM324, microcontroller AT89C51, optocoupler PC817, regulator 7805 and
an LCD module. Port pins P2.0 through P2.2 of the AT89C51 (IC2) are used to
sense the water level, while pins P2.3 and P2.4 are used to sense the
under-voltage and over-voltage, respectively. Pin P3.4 is used to control relay
RL1 with the help of optocoupler IC3 and transistor T5 in the case of
under-voltage, over-voltage and different water-level conditions. The LM324
(IC1) is a quad operational amplifier (op-amp). Two of its op-amps are used as
comparators to detect under- and over-voltage. In normal condition, output pin
7 of IC1 is low, making pin P2.3 of IC2 high. When the voltage at pin 6 of N1
goes below the set reference voltage at pin 5 (say, 170 volts), output pin 7 of
N1 goes high. This high output makes pin P2.3 of IC2 low, which is sensed by
the microcontroller and the LCD module shows ‘low voltage.’
In normal condition, pin 1 of N2 is high. When the voltage at pin 2 of N2 goes
above the set voltage at pin 3, output pin 1 of N2 goes low. This low signal is
sensed by the microcontroller and the LCD module shows ‘high voltage.’
Presets VR1 and VR2 are used for calibrating the circuit for under- and
over-voltage, respectively. When water in the tank rises to come in contact
with the sensor, the base of transistor BC548 goes high. This high signal
drives transistor BC548 into saturation and its collector goes low. The low
signal is sensed by port pins of microcontroller IC2 to detect empty tank, dry
sump and full tank, respectively.
When water in the tank is below
sensor A, the motor will switch on to fill water in the tank. The LCD module
will show ‘motor on.’ The controller is programmed for a 10-minute time
interval to check the dry-run condition of the motor. If water reaches sensor B
within 10 minutes, the microcontroller comes out of the dry-run condition and
allows the motor to keep pushing water in the tank. The motor will remain ‘on’
until water reaches sensor C. Then it will stop automatically and the
microcontroller will go into the standby mode. The LCD module will show ‘tank
full’ followed by ‘standby mode’ after a few seconds. The ‘standby mode’
message is displayed until water in the tank goes below sensor A. In case water
does not reach sensor B within 10 minutes, the microcontroller will go into the
dry-running mode and stop the motor for 5 minutes, allowing it to cool down.
The LCD module will show ‘dry-sump1.’ After five minutes, the microcontroller
will again switch on the motor for 10 minutes and check the status at sensor B.
If water is still below sensor B, it will go into the dry-running mode and the
LCD module will show ‘dry-sump2.’ The same procedure will repeat, and if the
dry-run condition still persists, the display will show ‘dry-sump3’ and the
microcontroller will not start the motor automatically. Now you have to check
the line for water and manually reset the microcontroller to start operation.
In the whole procedure, the microcontroller checks for high and low voltages.
For example, when the voltage is high, it will scan for about two seconds to
check whether it is a fluctuation. If the voltage remains high after two
seconds, the microcontroller will halt running of the motor. Now it will wait
for the voltage to settle down. After the voltage becomes normal, it will still
check for 90 seconds whether the voltage is normal or not. After normal
condition, it will go in the standby mode and start the aforementioned
procedure.
circuit diagram
note :
it was a efy project . the source code has been published on their
website.
