Unique Water Pump Controller - Seminar Report

Unique Water Pump Controller
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.

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.

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.

Design of PCB is a major step in the production of PCBs. It forms a distinct factor in electronic circuit performance and reliability. The productivity of a PCB, its assembly and serviceability also depends on its design.
The designing of a PCB consists of designing of the layout followed by the preparation of the artwork. The layout should include all the relevant details of the PCB design, while the artwork preparation brings it to the form required for the production of the production process. Hence a concept, clearly defining all the details of the circuit and partly of the equipments is a prerequisite before the actual layout can start. Depending on the accuracy required, the artwork might be produced on a 1:1 or 2:1 or even 4:1 scale. It is best prepared on a 1:1 scale. Since the layout for our circuit was already available, we did not have to implement these procedures.

Initially the board outlines and connectors are marked on a sheet of paper followed by sketching the component outlines with connecting points and the conductor patterns. Prepare the layout as viewed from the component side so as to avoid confusion. The layout is developed in the direction of signal flow, as far as possible. This reduces the number of interconnections.
Among the components, the larger ones are placed first and the space in between is filled with smaller ones. Components requiring input/output connections come near the connectors. All the components are placed in such a way that desoldering of other components is not necessary, if they have to be replaced.
The PCB layout may be divided into functional sub units. Each of these sub units is realized on a defined portion of the board. This improves functional reliability and enables faster testing and servicing of the board.
While designing the conductors, the minimum spacing requirements for the final artwork should be known. It depends on a number of factors and it is based on the breakthrough voltage. But, in any case, the minimum spacing is applied only where it cannot be avoided. The yield in PCB fabrication will otherwise come down, with minimum spacing.
The final copper pattern is formed by selective removal (ETCHING) of the unwanted copper, which is not protected by an electric resist (ferric chloride).
Many factors are considered while choosing the most suitable etchant system for a PCB process. The etch resist should be compatible with the etchant. Besides, the etching speed, copper showing capacity, etchant price and pollution characteristics come into the picture of the overall economy of the etchant. Some commonly used etchants are ferric chloride, cupric chloride, chromic acid and alkaline ammonia. After etching is completed, FeC13 is washed from the board and is cleaned dry. The paint is removed using suitable solvents. Holes are now drilled into the appropriate positions. Drill bits of correct dimensions are then soldered into the PCB carefully. Care should be taken to give the PCB the best appearance possible. 

Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Solder the white LEDs-LDR assembly on a separate PCB and use a separate power supply for it. Mount LEDs behind the LDR. Otherwise light from the LEDs will affect the working of the circuit. Connect LDR to the main circuit board at ‘A’ and ‘B’ points.
Fix the LEDs-LDR assembly on the inner side of the water-tank cap (fig.3). Orient the LEDs and the LDR such that when the water tank is full, the light emitted from the LEDs and reflected from the water surface falls directly on LDR. The distance between the upper level of water and the LEDs-LDR setup should be minimal, ensuring that water doesn’t touch LDR. By using more white LEDs, this distance can be increased. Cover the LDR with a black tube to increase its sensitivity.
Also fix the main unit at a convenient place and connect it to the LEDs-LDR assembly through wire. Select the relay (12V, 1C/O RELAY) according to the horse-power (HP) of the water pump. After arranging the setup (with maximum water in the tank), adjust variable resistor VR (10K, PRESET) until LED1 stops glowing. (LED1 is used as an indicator to show whether the pump is ON or OFF). In this state, the relay should de-energize. When the water level decreases, the relay automatically energizes to connect the mains to the motor and it starts pumping water. 

From this project, it is clear that we are able to design a circuit based on Linear Integrated Circuits. Further we came to know about the working of Light Dependent Resistor (LDR), Operational Amplifier, Switching Diode, Transistor and Relay Circuit.   
This project is accessible to any one with an average expense and a bit of dedicated work, as we have realized in materializing it. We conclude that this project may give as commercial product which will be useful to every one.

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