Handwash Circuit

1.INTRODUCTION

It has become our prime duty to conserve our resouces. This project is an automatic hand wash circuit which conserves water and poperates only when an obstacle comes under it. The IR beam gets reflected when an obstacle come and the circuit is triggered. The circuit is a very simple circuitry using high quality transmitter and receiver. Transmitter produces IR beam, which gets reflected when an obstacle comes and is received by the IR detector diode. The diode gets forward biased and thus voltage fllow varis causing variation in the pin voltage. This increases the transistor current. This current drives the valve of the water pipe.

2.  BLOCK DIAGRAM OF HANDWASH CIRCUIT

3. BLOCK DIAGRAM DESCRIPTION

3.1 OVERALL DESCRIPTION:

The block diagrm consists of the following blocks

·         Transmitter

·         Receiver

·         Triggering circuit

·         Valve drive circuit

The transmitter is basically an oscillator which produces continuous IR beam of 38KHz frequency. When an obstacle comes, the IR beam gets reflected to the IR diode,and reaches the receiver section. The signal is then transmitted to the triggering circuit, which then produces current to drive the valve circuit.

3.2 TRANSMITTER:

It  is basically an astable multivibrator which produces pulses of 38KHz frequency. It is then output as IR beam by the IR LED

3.3 RECEIVER:

It is an IR diode, which receives IR beam reflected by the obstacle and then conducts causing variation in the voltage across it.

3.4 TRIGGERING CIRCUIT:

The triggering circuit is mainly a comparator and its output toggles when there is a pin voltage variation caused by the receiver output.

3.5 VALVE DRIVE CIRCUIT:

The valve drive circuit consists of a transistor. When it receives the trigger from the triggering circuit, a large collector current flows and this will drive the valve.

4. CIRCUIT DIAGRAM

5. DESCRIPTION OF CIRCUIT DIAGRAM

The first section of the circuit is a transmitter, which is designed using an astable multivibrator which is an oscillator, producing a pulse of constant frequency,38KHz. this is emitted as IR beam using an IR LED. The receiver consists of an IR diode, which is capable of conducting when it receives the reflected IR beam. Thus, the voltage across it decreases and this is then input to a comparator, which compares the pin voltage difference to the Vcc. The output of the comparator toggles. This is fed to the valve driver circuit, which comprises of a transistor. The transistor conducts and produces large collector current enough to turn on the valve and the water flows.

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6. COMPONENTS REQUIRED

COMPONENTS	SPECIFICATION	QUANTITY
IC	NE555	1
Op amp	LM311	1
Transistor	2N1613 SL100
Diode	LED-55B/TO LTR-516	1 1
Resistors	470k 100k 10k 47k 22k 1k 33k	2 1 1 1 1 1 1
Capacitors	1uF .1uF 22 uF	1 1 2

7. DESCRIPTION OF THE COMPONENTS

7.1 .NE555:

7.1.1 DESCRIPTION:

The NE555  is a highly stable controller capable of  producing  accurate timing pulses. With a monostable operation, the  time  delay is  controlled by one external resistor and one capacitor. With an astable operation, the frequency and duty cycle are accurately controlled by two external resistors  and one capacitor.

7.1.2  FEATURES:

·         High Current Drive Capability (200mA)

·         Adjustable Duty Cycle

·         Temperature Stability of 0.005%/°C

·         Timing From µSec to Hours

·         Turn off Time Less Than 2µSec

7.1.3 APPLICATIONS

• Precision Timing

• Pulse Generation

• Time Delay Generation

• Sequential Timing  

7.2 2n1613:

FEATURES

• Low current (max. 500 mA)

• Low voltage (max. 50 V).

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7.2.1 APPLICATIONS

• High-speed switching and amplification.

7.2.2 DESCRIPTION

NPN medium power transistor in a TO-39 metal package.

7.3 .SL100

SL100 is a general purpose, medium power NPN transistor. It is mostly used as switch in common emitter configuration. The transistor terminals require a fixed DC voltage to operate in the desired region of its characteristic curves. This is known as the biasing. For switching applications, SL100 is biased in such a way that it remains fully on if there is a signal at its base. In the absence of base signal, it gets turned off completely. 

The emitter leg of SL100 is indicated by a protruding edge in the transistor case. The base is nearest to the emitter while collector lies at other extreme of the casing.

7.4.LED55/TO

An IR LED, also known as IR transmitter, is a special purpose LEDthat transmits infrared rays in the range of 760 nm wavelength. Such LEDs are usually made of gallium arsenide or aluminium gallium arsenide. They, along with IR receivers, are commonly used as sensors.

The appearance is same as a common LED. Since the human eye cannot see the infrared radiations, it is not possible for a person to identify whether the IR LED is working or not, unlike a common LED. To overcome this problem, the camera on a cellphone can be used. The camera can show us the IR rays being emanated from the IR LED in a circuit.

7.5.LTR 516:

7.5.1 FEATURES:

·         Highly photosensitive

·         Suitable for IR radiation

·         Low juncton capacitance

·         High cut off frequency

·         Fast switching time

·       It is a special dark green plastic package that cut the visible light and suitable for detectors of IR applications.

7.6 .LM 311

7.6.1 Description

The LM311 series is a monolithic, low input current voltage comparator. The device is also designed to operate from dual or single supply voltage.

7.6.2 Features

·         Low input bias current : 250nA (Max)

·         Low input offset current : 50nA (Max)

·         Differential Input Voltage : ±30V

·         Power supply voltage : single 5.0V supply to ±15V.

·         Offset voltage null capability.

·       Strobe capability.

7.7 RESISTORS

A resistor is a two- terminal passive electronic component that implement electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. This constant of proportionality is called conductance, G. The reciprocal

of the conductance is known as the resistance R, since, with a given voltage V, a larger value of R further "resists" the flow of current I as given by Ohm’s law:

7.8 CAPACITOR:

A capacitor (formerly known as condenser) is a device for storing electric charge. The forms of practical capacitors vary widely, but all contain at least two conductors separated by a non-conductor. Capacitors used as parts of electrical systems, for example, consist of metal foils separated by a layer of insulating film.

A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectic (insulator). When there is a potential difference  (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them.

Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current  to pass, in filter networks, for smoothing the output of power supplies in the resonant circuits that tune radios to particular frequencies and for many other purposes.

The capacitance is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are often called "plates," referring to an early means of construction. In practice the dielectric between the plates passes a small amount ofleakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance.

8. PCB FABRICATION

The printed circuit board (PCB) provides the electrical interconnections between various components and as well as provides mechanical support to the components. The components are soldered to the PCB. The quality of soldering directly affects the reliability of the circuit. The procedure for fabricating the PCB for any general project is described below.

The printed circuit board consist the following steps.

1.      Lay out preparation

2.      Artwork Preparation

3.      Film Master Production

4.      Pattern transfer

5.      Etching

6.      Drilling

8.1 LAYOUT PREPARATION     

The layout is commonly prepared in the scale of 2:1. It offered a reasonable compromise below accuracy gained and handling convenience 2:1 artwork as the actual PCB area. Grid systems are commonly used for preparing the layout. The use of the grid sheet gives more convenience in placement of components and conductors. The grid system based on 0.1 is found to be too coursing, a grid equidistant of 0.025 or even 0.1 mm is recommended.    

 Procedure

1.      Each and every PCB layout is viewed from component side.

2.      The designing of the layout is started with an absolutely clear component list and circuit diagram is available.

3.      The larger component are placed first and the space in between is filled with area

4.       In the designing of the PCB layout, It is very importance to divide the circuit in to functional sub units. Each of these sub units are realized in the defined the portion of the board.

5.      The components are placed in the grid sheet tanning the standard length and width.

6.      The punched lay out is circled to taking the standard size of the land pads

7.       These pads are entering connected as the circuit diagram.

8.      The mirror image of these gives the solder side of the PCB.

8.2  PATTERN TRANSFER

          After the film is processed the film master are obtained. The transfer of the conductor which on film master on to the copper clad base material is done by two methods mainly photo printing and screen printing. Photo printing is extremely accurate process which is also applied to the fabrication of semi-conductors. Screen printing is comparatively cheap and simple method for transfer although less precise then photo printing. But this is less costly, this method is commonly used.

8.3  SCREEN PRINTING

In screen printing, the process is very simply. A screen fabric with uniform meshes and opening is stretched and fixed on a solid frame of metal or wood. The circuit pattern is photographically transferred on to screen, leaving the meshes in the rest of area as closed. In the actual printing step ink is forced by moving queue through the open master on to the surface of the material to be printed. The light sensitive material is coated on to the screen and using film master the pattern is transferred to the screen. The using ink and the pattern is transferred to the copper clad sheet.

Two methods are used for screen printing into screen

1.     Direct method

2.     Indirect method.

            In direct method than photographically sensitive emulsions are used for transferring patterns. The Wet material is uniformly coated to the screen and then exposed. In indirect method, the photographically sensitive film is transferred to screen. The film is exposed and ten it sticker in to the screen. The pattern is then transferred to the screen using the links and squeegee.

8.4 ETCHING

The removal of unwanted copper from the copper clad sheet is known as etching. For this 4 types of tanks are used.

1.     Ferric chloride

2.     Cupric chloride

3.     Chromic acid

4.     Alkaline ammonia

            Among these ferric chloride is cheap and popular etchant is ferric chloride and also suited for home and industrial applications. The high corrosive powers of ferric chloride lead to shot etching time and little under etching. Ferric chloride matches well photo and screen printed resists

8.5 DRILLING

Drilling of component mounting holes in to PCBs is by the most important mechanical machining operation PCB production process. The importance of the whole drilling on PCB has further group with electronic component miniaturization and its need for smaller whole

diameters and higher package density where whole purchasing is practically routed out. Four types of drilling are commonly used

1.      Drilling by direct sight.

2.      Drilling by optical slight.

3.      Jig drilling.

4.      NC drilling.

8.6 COMPONENT MOUNTING

Components are basically mounted on one side of the board. On polarized two lead components are mounted to give the marking or orientation throughout the board. The component orientation can be both Horizontal as well as vertical but uniformly, directions are placed. The Uniformity in orientation of polarizes components is determining during design of PCB.

Some recommended mounting techniques are given below

Horizontally mounted resister must touch the board resister to avoid lifting of solder along with the copper pattern under pressure on the resister body Vertical mounted resister should not be flash to board surface to avoid the Strain on the solder joint as well as the component need to junction due to Different thermal expansion coefficient of lead board material also where necessary spaces should be provided. Coated or sealed components have to be mounting such a way as to provide a certain distance from the board. When jumper wires cross over the conductors, jumper wire must be insulated. Transistors mounting should be never done flash to be board. This could give considerable stress on the solder joints and to the lead connection beside the possible over heating during the soldering op[[[erations.

9. SOLDERING

Soldering is the process of two or more similar or dissimila metals by meling another metal having lower melting point

9.1 SOLDERING FLUXES:

In order to make the surface accept the solder readily, the component terminal shoud be free from oxides and other obstructing films. Soldering flux cleans the oxides from the surface of the metal. Zinc chloride, Aluminium chloride and Rosin anre othe commonly used fluxes.

9.2 .SOLDER:

Solder is used for joining two or more metal at emperature below their melting point. The popularly used solder are alloy of Tin that melts at 375F and solidifies when it cools.

9.3 SOLDERING IRON

It is used to melt the solder and apply at the joints in the circuit.

10. PCB LAYOUT

11. MERITS

·         It has a motorised valve

·         It is easy to handle

·         Circuit is highly stable

·         It has a wide range of supply voltage

·         It is easy to fix

·         It performs low current and low voltage operation

·         Low cost

12. DEMERTS

·         It is big in size

·         Small variation in component values can make the circuit over sensitive.

13. APPLICATIONS

It can be used in houses, hotels, shopping complexes etc.

14. CONCLUSION

The hand wash circuit has been successfully designed and implemented. The main advantage of this is that it conserves water and is user friendly.

15. FUTURE SCOPE

It has a great scope in future as the resources are being finished up and technology is sophisticating. It can be converted into super active water taps and will be of great application.

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