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INTRODUCTION
The Unique Water Pump Controller mainly used for controlling (switch ON or OFF) the Pump according to the water-level of the tank. That is when the water-level is high enough, the circuit will switch ON the Pump and when the water-level is low, the circuit will switch OFF the Pump.
The main parts of this circuit are Sensor Circuit, Voltage Comparator, Switching Circuit, Relay Circuit and the Water Pump. The sensor will sense the water level by using reflection of light and then an indication is given to the non-inverting input of Voltage Comparator. The comparator produces an output corresponding to the input at the non-inverting input. The switching circuit will close or open the Relay Circuit according to the output of Comparator. The Relay Circuit controls the working of the Water Pump. That is it will close or open the N/O switch according to the state of switching circuit.
The two advantages of this circuit are, (a) The water level never goes below a particular level and (b) No modification in the water tank is required.
BLOCK DIAGRAM
The Functional Block Diagram of the Unique Water Pump Controller mainly consists of five Blocks.
1. Sensor Circuit.
2. Voltage Comparator.
3. Switching Circuit.
4. Relay Circuit.
5. Water Pump.
CIRCUIT OPERATION
When the water level is high enough, light from the white LEDs (LED1 through LED3) reflects to fall on LDR (Light Dependent Resistor). (Note: The light reflected from the water tank is used to control the resistance of LDR). This reduces the resistance of LDR and thereby increasing the voltage at the non-inverting input terminal (pin no.3) of the IC (µA741). This IC is used in the circuit as a voltage comparator. Resistors R4 and R5 form a potential divider to fix half of supply voltage to the inverting input (pin no.2) of IC.
Normally, when the water is full, LDR gets more of the reflected light because the distance between the water level and the face of LDR is minimal. When white light falls on LDR, the voltage at the non-inverting input of IC increases and its output goes high. This high output makes PNP transistor (BC558) non-conducting and the relay remains de-energized. Since the water-pump power supply is connected to the normally-open (N/O) contacts of relay, pumping is stopped.
When water level falls, the amount of light reflected to LDR decreases and its resistance increases. This reduces the voltage at pin 3 of IC and its output goes low. This low output from IC makes transistor conduct. Thus the relay energizes to close the N/O contacts and the motor starts pumping water.