Automatic IR Tap Controller

Automatic IR Tap Controller

CHAPTER 1

INTRODUCTION

Department of Electronics & Instrumentation Page 1


INTRODUCTION

Automatic wash basin tap controller is an Infrared based system that

detects any interruption of the IR rays by our hands or utensils and water

automatically starts flowing out of the tap.

The circuit mainly comprises Transmitter & Receiver which are built with

the 555 Timer. Both require 5 volts D.C. Supply. The IR rays continuously

emitted by the transmitter fall on the receiver. We have used an IR sensor –

TSOP1738 and an infra-red LED. A relay is used in the circuit along with

the free-wheeling diode to drive the solenoid. Solenoid is used to lift up the

valve fitted in the pipe to let the water flow out of the tap. The circuit is

simple, economical and finds wide application in daily life.

The aim of this project is to design an Automatic Wash Basin Tap Controller

using 555 timer, IR LED and infrared sensor. The overall module should be

miniature to allow portability and should be economical.



CHAPTER 2

POWER SUPPLY2.1 Building the 5V Regulated Power Supply2.2 Transformer Output2.3 Rectifier Output2.4 Smoother Output



POWER SUPPLY

A simple power supply circuit that includes each of these blocks in given in figure 4. The following articles in this series look at each block of the Power Supply in detail, but if you just want to build a 5V regulated Power Supply.



2.1 Building the 5V Regulated Power Supply

Figure gives a strip board layout for the 5V regulated power supply shown in figure 4. The layout does not include the transformer block, so the input to the board needs to be 7 - 35V AC from a suitable transformer. The layout includes space for two optional 2-way screw terminal blocks to make connecting up the power supply easier.

If the input voltage is 9V AC, you will be able to draw 1A from the power supply. For the maximum input voltage of 35V you will be able to draw 0.1A.

2.2 TRANSFORMER OUTPUT

A suitable ready-built mains power supply unit, such as those used to control model trains, will include a transformer. I wouldn't recommend building your own due to the safety considerations when dealing with mains voltages. If such a unit does not incorporate smoothing, rectification, and regulation, then you will need to build these blocks as described in part 1 of this series.

If the unit does not have a fuse or a cut-out on the output of the transformer, you will also need to add a fuse of an appropriate rating. This fuse is in addition to the mains fuse in the unit's plug and is needed to protect the low voltage winding of the transformer and any circuits you connect to it. Although we won't be building the transformer block of our 5V regulated power supply, it is interesting to know how it works.



How Transformers Work

A transformer consists of two coils (often called 'windings') linked by an iron core, as shown in figure 1. There is no electrical connection between the coils, instead they are linked by a magnetic field created in the core.

Transformers are used to convert electricity from one voltage to another with minimal loss of power. They only work with AC (alternating current) because they require a changing magnetic field to be created in their core. Transformers can increase voltage (step-up) as well as reduce voltage (step-down).

Alternating current flowing in the primary (input) coil creates a continually changing magnetic field in the iron core. This field also passes through the secondary (output) coil and the changing strength of the magnetic field induces an alternating voltage in the secondary coil. If the secondary coil is connected to a load the induced voltage will make an induced current flow. The correct term for the induced voltage is 'induced electromotive force' which is usually abbreviated to induced emf.

The iron core is laminated to prevent 'eddy currents' flowing in the core. These are currents produced by the alternating magnetic field inducing a small voltage in the core, just like that induced in the secondary coil. Eddy currents waste power by needlessly heating up the core but they are reduced to a negligible amount by laminating the iron because this increases the electrical resistance of the core without affecting its magnetic properties.



Transformers have two great advantages over other methods of changing voltage:They provide total electrical isolation between the input and output, so they can be safely used to reduce the high voltage of the mains supply. Almost no power is wasted in a transformer. They have a high efficiency (power out / power in) of 95% or more.

2.3 Rectifier Output

The purpose of a rectifier is to convert an AC waveform into a DC waveform. There are two different rectification circuits, known as 'half-wave' and 'full-wave' rectifiers. Both use components called diodes to convert AC into DC.

A diode is a device which only allows current to flow through it in one direction. In this direction, the diode is said to be 'forward-biased' and the only effect on the signal is that there will be a voltage loss of around 0.7V. In the opposite direction, the diode is said to be 'reverse-biased' and no current will flow through it.

The Full-wave Rectifier

The circuit in figure addresses the second of these problems since at no time is the output voltage 0V. This time four diodes are arranged so that both the positive and negative parts of the AC waveform are converted to DC. The resulting waveform is shown in figure.





When the AC input is positive, diodes A and B are forward-biased, while diodes C and D are reverse-biased. When the AC input is negative, the opposite is true - diodes C and D are forward-biased, while diodes A and B are reverse-biased.

One disadvantage of the full-wave rectifier is that there is a voltage loss of 1.4V across the diodes. Why not 2.8V as there are four diodes? Remember that only two of the diodes are passing current at any one time

While the full-wave rectifier is an improvement on the half-wave rectifier, its output still isn't suitable as a power supply for most circuits since the output voltage still varies between 0V and Vs-1.4V. So, if you put 12V AC in, you will 10.6V DC out.

2.4 Smoother Output

Most circuits will require 'smoothing' of the DC output of a rectifier, and this is a simple matter since it involves only one capacitor, as shown in figure.

The output waveform in figure shows how smoothing works. During the first half of the voltage peaks from the rectifier, when the voltage increases, the capacitor charges up. Then, while the voltage decreases to zero in the second half of the peaks, the capacitor releases its stored energy to keep the output voltage as constant as possible. Such a capacitor is called a 'smoothing' or 'reservoir' capacitor when it is used in this application.



RIPPLE

If the voltage peaks from the rectifier were not continually charging up the capacitor, it would eventually discharge and the output voltage would decrease all the way down to 0V. The discharging that does occur between peaks gives rise to a small 'ripple' voltage. The amount of ripple is affected by a combination of three factors:

The value of the capacitor. The larger the capacitor value, the more charge it can store, and the slower it will discharge. Therefore, smoothing capacitors are normally electrolytic capacitors with values over 470μF.

The amount of current used by the circuit. If the circuit connected to the power supply takes a lot of current, the capacitor will discharge more quickly and there will be a higher ripple voltage. The frequency of the peaks. The more frequent the voltage peaks from the rectifier, the more often the capacitor will be charged, and the lower the ripple voltage will be. If you want to calculate the ripple voltage, you can use this formula...

Where Vr is the ripple voltage in Volts, I is the current taken by the circuit in Amps, C is the value of the smoothing capacitor in Farads, and F is the frequency of the peaks from the full-wave rectifier, in Hertz. This frequency will be double the normal mains frequency, i.e. 100Hz in the case of the UK mains supply, or 120Hz in the case of the US mains supply.

The ripple voltage should not be more than 10% of Vs - if it is, increase the value of the smoothing capacitor.

Lots of circuits will work fine from a smoothed power supply, but some must have a completely regular supply with no ripple voltage



2.5 Regulator Output

While there are many circuits that will tolerate a smoothed power supply, some must have a completely regular supply with no ripple voltage. This article discusses regulator ICs which can provide this regular power supply.There are many types of regulator IC and each type will have different pin-outs and will need to be connected up slightly differently. Therefore, this article will only look at one of the common ranges of regulator, the 78xx series.

There are seven regulators in the 78xx series, and each can pass up to 1A to any connected circuit. There are also regulators with similar type numbers that can pass a higher or lower current, as shown in the table below. In addition, variable regulators are available, as are regulators that can provide negative regulation voltages for circuits that require them.



CHAPTER 3

PRINTED CIRCUIT BOARD3.1 Materials3.2 Steps for PCB Designing



PRINTED CIRCUIT BOARD

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. Alternative names are printed wiring board (PWB),and etched wiring board. A PCB populated with electronic components is a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA).PCBs are rugged, inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are much cheaper and faster for high-volume production. Much of the electronics industry's PCB design, assembly, and quality control needs are set by standards that are published by the IPC organization.

3.1 Materials

Conducting layers are typically made of thin copper foil. Insulating materials have a wider scale: Phenolic paper, glass fiber and different plastics are commonly used. Usually PCB factories use prepregs (short for preimpregnated), which are a combination of glass fibre mat, nonwoven material and resin. Copper foil and prepreg are typically laminated together with epoxy resin. Well known prepreg materials used in the PCB industry are FR-2 (Phenolic cotton paper), FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and epoxy), FR-5 (Woven glass and epoxy), FR-6 (Matte glass and polyester), G-10 (Woven glass and epoxy), CEM-1 (Cotton paper and epoxy), CEM-2 (Cotton paper and epoxy), CEM-3 (Woven glass and epoxy), CEM-4 (Woven glass and epoxy), CEM-5 (Woven glass and polyester). Other widely used materials are polyimide, Teflon and some ceramics.



3.2 STEPS FOR PCB DESIGNING

1. Patterning (etching)

The vast majority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides, (creating a "blank PCB") then removing unwanted copper after applying a temporary mask (eg. by etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps.

There are three common "subtractive" methods (methods that remove copper) used for the production of printed circuit boards:

Silkscreen printing uses etch-resistant inks to protect the copper foil. Subsequent etching removes the unwanted copper. Alternatively, the ink may be conductive, printed on a blank (non-conductive) board. The latter technique is also used in the manufacture of hybrid circuits.

Photoengraving uses a photo mask and chemical etching to remove the copper foil from the substrate. The photo mask is usually prepared with a photo plotter from data produced by a technician using CAM, or computer-aided manufacturing software.

Laser-printed transparencies are typically employed for photo tools; however, direct laser imaging techniques are being employed to replace photo tools for high-resolution requirements.

PCB milling uses a two or three-axis mechanical milling system to mill away the copper foil from the substrate. A PCB milling machine (referred to as a 'PCB Prototype') operates in a similar way to a plotter, receiving commands from the host software that control the position of the milling head in the x, y, and (if relevant) z axis. Data to drive the Prototyper is extracted from files generated in PCB design software and stored in HPGL or Gerber file format.



"Additive" processes also exist. The most common is the "semi-additive" process. In this version, the unpatented board has a thin layer of copper already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this mask exposes those parts of the substrate that will eventually become the traces.) Additional copper is then plated onto the board in the unmasked areas; copper may be plated to any desired weight. Tin-lead or Other surface plating’s are then applied. The mask is stripped away and a brief etching step removes the now-exposed original copper laminate from the board, isolating the individual traces.

The additive process is commonly used for multi-layer boards as it facilitates the plating-through of the holes (to produce conductive vias) in the circuit board.

2. Drilling

Holes, or vias, through a PCB are typically drilled with tiny drill bits made of solid tungsten carbide. Automated drilling machines perform the drilling with placement controlled by a drill tape or drill file. These computer-generated files are also called numerically controlled drill (NCD) files or "Excellon files". The drill file describes the location and size of each drilled hole.

When very small vias are required, drilling with mechanical bits is costly because of high rates of wear and breakage. In this case, the vias may be evaporated by lasers. Laser-drilled vias typically have an inferior surface finish inside the hole. These holes are called micro vias.

It is also possible with controlled-depth drilling, laser drilling, or by pre-drilling the individual sheets of the PCB before lamination, to produce holes that connect only some of the copper layers, rather than passing through the entire board. These holes are called blind vias when they connect an internal copper layer to an outer layer, or buried vias when they connect two or more internal copper layers and no outer layers.

The walls of the holes, for boards with 2 or more layers, are plated with copper to form plated-through holes that electrically connect the conducting layers of the PCB. For multilayer boards, those with 4 layers or more, drilling typically produces a smear comprised of the bonding agent in the



Laminate system. Before the holes can be plated through, this smear must be removed by a chemical de-smear process, or by plasma-etch.

3. Solder resist

Areas that should not be soldered to may be covered with a polymer solder resist (solder mask) coating. The solder resist prevents solder from bridging between conductors and thereby creating short circuits. Solder resist also provides some protection from the environment.

4. Printed circuit assembly

After the printed circuit board (PCB) is completed, electronic components must be attached to form a functional printed circuit assembly, or PCA (sometimes called a "printed circuit board assembly" PCBA). In through-hole construction, component leads are inserted in holes. In surface-mount construction, the components are placed on pads or lands on the outer surfaces of the PCB. In both kinds of construction, component leads are electrically and mechanically fixed to the board with a molten metal solder.

There are a variety of soldering techniques used to attach components to a PCB. High volume production is usually done with machine placement and bulk wave soldering or reflow ovens, but skilled technicians are able to solder very tiny parts (for instance 0201 packages which are 0.02" by 0.01") by hand under a microscope tweezers and a fine tip soldering iron for small volume prototypes. Some parts are impossible to solder by hand, such as Ball Grid Array (BGA) packages.

Often, through-hole and surface-mount construction must be combined in a single PCA because some required components are available only in surface-mount packages, while others are available only in through-hole packages. Another reason to use both methods is that through-hole mounting can provide needed strength for components likely to endure physical stress, while components that are expected to go untouched will take up less space using surface-mount techniques.



After the board is populated, the populated board may be tested. While the power is off, visual inspection, automated optical

inspection. JEDEC guidelines for PCB component placement, soldering, and inspection are commonly used to maintain quality control in this stage of PCB manufacturing.

While the power is off, analog signature analysis, power-off testing. While the power is on, in-circuit tests, where physical measurements

(i.e. voltage, frequency) can be done. While the power is on, functional test, just checking if the PCB does

what it had been designed for.

To facilitate these tests, PCBs may be designed with extra pads to make temporary connections. Sometimes these pads must be isolated with resistors. The in-circuit test may also exercise boundary scan test features of some components. In-circuit test systems may also be used to program nonvolatile memory components on the board.In boundary scan testing, test circuits integrated into various ICs on the board form temporary connections between the PCB traces to test that the ICs are mounted correctly. Boundary scan testing requires that all the ICs to be tested use a standard test configuration procedure, the most common one being the Joint Test Action Group (JTAG) standard.



CHAPTER 4

DESIGN OBJECTIVE



DESIGN OBJECTIVE

The aim of this project is to design an Automatic Wash Basin Tap Controller using 555 timer, IR LED and infrared sensor (TSOP1738). The overall module should be miniature to allow portability. It has the following features.

Easy to use

Economical

Compact and portable

The main advantage of this device is its miniature size and satisfactory performance, considering its low cost and small size.



CHAPTER 5

SPECIFICATIONS5.1 IC 555 Timer5.2 IR Sensor TSOP 17385.3 IR LED 38



SPECIFICATIONS

Name Description Specifications Number of components required

RES Resistor 1K=4,22OHM=1, 1.5K=1,

10K=1,100K =1, VAR 20 K =1

9

CAP Capacitor 0.001,6.8,4.7,100=2, 0.01=2 micro farads

7

VDC Dc voltage source

5 volts 2

GND Ground 0 volts 3

REL Relay - 1

IC 555 Timer - 2

LED IR Infra-red LED - 1

TRANS Transistor BC548

- 2



5.1 SPECIFICATIONS OF IC555

Supply voltage (VCC) 4.5 to 15 V

Supply current (VCC = +5 V) 3 to 6 mA

Supply current (VCC = +15 V) 10 to 15 mA

Output current (maximum) 200 mA

P Power dissipation 600 mW

Operating temperature 0 to 70° C

5.2 SPECIFICATION OF IR SENSOR TSOP 1738

Supply voltage (VCC) 5 V

Integrated Oscillator 38 KHz

Output Voltage (active at level 0) 5 V


P Power Consumption 0.4 to 1.0 mA

Operating temperature -25 to 80 O C

Angle of Detection 90O

Dimensions of Casing12.5 x 10 x Thickness 5.8



5.3 SPECIFICATION OF IR LED 38:

Peak Emission Wavelength 3.8 µm

Spectral Bandwidth (FWHM) 0.4 µm

Radiant Output Power 60 µW


Operating currents 500-600 mA

Rise time 200 ns

Field of View 60O



CHAPTER 6

CIRCUIT COMPONENTS 6.1 IC 555 Timer6.2 IR Light Emitting Diodes (LEDs)6.3 IR Sensor TSOP 17386.4 Relay6.5 Solenoid6.6 Resistors6.7 Free Wheeling Diode6.8 Capacitors6.9 Transistors



CIRCUIT COMPONENTS

6.1 IC555 TIMER

DESCRIPTION

The 555 timer IC was first introduced around 1971 by the Signetics Corporation as the SE555/NE555 and was called "The IC Time Machine" and was also the very first and only commercial timer IC available. The 555 is a monolithic timing circuit that can produce accurate and highly stable time delays or oscillations. It has an adjustable duty cycle ,timing is from microseconds to hours. It has a high current output ,it can source or sink 200 miliamperes . It can operate in one of the two modes either as a monostable (one-shot) multivibrator or as an astable (free running) multivibrator .It can be used in dc-dc converters, digital logic probes, waveform generators, analog frequency meters and tachometers, temperature measurement and control ,infrared transmitters ,burglar and toxic gas alarms ,voltage regulators ,electric eyes and many others.

THE 555 INTERNAL CIRCUITS



PIN OUT The 555 comes in 2 packages, either the round metal-can called the 'T' package or the more familiar 8-pin DIP 'V' package. The 556 timer is a dual 555 version and comes in a 14-pin DIP package, the 558 is a quad version with four 555's also in a 14 pin DIP package.



PIN DESCRIPTION

Pin1: Ground. All voltages are measured with respect to this terminal.

Pin2: Trigger. The output of the timer depends on the amplitude of the external trigger pulse applied to this pin. The output is low if the voltage at this pin is greater than 2/3 VCC. When a negative going pulse of amplitude greater than 1/3 VCC is applied to this pin, comparator 2 output goes low, which in turn switches the output of the timer high. The output remains high as long as the trigger terminal is held at a low voltage.

Pin3: Output. There are two ways by which a load can be connected to the output terminal: either between pin 3 and ground or between pin 3 and supply voltage +VCC. When the output is low the load current flows through the load connected between pin 3 and +VCC into the output terminal and is called sink current. The current through the grounded load is zero when the output is low. For this reason the load connected between pin 3 and +VCC is called the normally on load and that connected between pin 3 and ground is called normally off-load. On the other hand, when the output is high the current through the load connected between pin 3 and +VCC is zero. The output terminal supplies current to the normally off load. This current is called source current. The maximum value of sink or source current is 200mA.

Pin4: Reset. The 555 timer can be reset (disabled) by applying a negative pulse to this pin. When the reset function is not in use, the reset terminal should be connected to +VCC to avoid any possibility of false triggering.

Pin5: Control Voltage. An external voltage applied to this terminal changes the threshold as well as trigger voltage. Thus by imposing a voltage on this pin or by connecting a pot between this pin and ground, the pulse width of the output waveform can be varied. When not used, the control pin should be bypassed to ground with a 0.01µF Capacitor to prevent any noise problems.

Pin6: Threshold. This is the non-inverting input of comparator 1, which monitors the voltage across the external capacitor. When the voltage at this pin is greater than or equal to the threshold voltage 2/3 VCC, the output of comparator 1 goes high, which in turn switches the output of the timer low.



Pin7: Discharge. This pin is connected internally to the collector of transistor Q1. When the output is high Q1 is OFF and acts as an open circuit to external capacitor C connected across it. On the other hand, when the output is low, Q1 is saturated and acts as a short circuit, shorting out the external capacitor C to ground.

Pin8: +VCC. The supply voltage of +5V to + 18V is applied to this pin with respect to ground.

OPERATION

Initially when the circuit is in the stable state i.e , when the output is low, transistor Q1 is ON and the capacitor C is shorted to ground. Upon the application of a negative trigger pulse to pin 2, transistor Q1 is turned OFF, which releases the short circuit across the external capacitor C and drives the output high. The capacitor C now starts charging up towards VCC through R. When the voltage across the capacitor equals 2/3 VCC, comparator 1’s output switches from low to high, which in turn drives the output to its low state via the output of the flip-flop. At the same time the output of the flip-flop turns transistor Q1 ON and hence the capacitor C rapidly discharges through the transistor. The output of the monostable remains low until a trigger pulse is again applied. Then the cycle repeats.

The pulse width of the trigger input must be smaller than the expected pulse width of the output waveform. Also the trigger pulse must be a negative going input signal with amplitude larger than 1/3 VCC.

The time during which the output remains high is given by

T= 1.1 RC seconds.

Where R is in Ohms and C is in Farads.

Once triggered, the circuit’s output will remain in the high state until the set time, T elapses. The output will not change its state even if an input trigger is applied again during this time interval T. The circuit can be reset during the timing cycle by applying negative pulse to the reset terminal. The output will remain in the low state until a trigger is again applied.



OPERATING MODES

The 555 timer has two basic operational modes: one shot and astable. In the one-shot mode, the 555 acts like a monostable multivibrator. A monostable is said to have a single stable state--that is the off state. Whenever it is triggered by an input pulse, the monostable switches to its temporary state. It remains in that state for a period of time determined by an RC network. It then returns to its stable state. In other words, the monostable circuit generates a single pulse of fixed time duration each time it receives and input trigger pulse. Thus the name one-shot. One-shot multivibrators are used for turning some circuit or external component on or off for a specific length of time. It is also used to generate delays. When multiple one-shots are cascaded, a variety of sequential timing pulses can be generated.

MONOSTABLE OPERATION

In the basic circuit of the 555 connected as a monostable multivibrator an external RC network is connected between the supply voltage and ground. The junction of the resistor and capacitor is connected to the threshold input which is the input to the upper comparator. The internal discharge transistor is also connected to the junction of the resistor and the capacitor. An input trigger pulse is applied to the trigger input, which is the input to the lower comparator. With that circuit configuration, the control flip-flop is initially reset. Therefore, the output voltage is near zero volts. The signal from the control flip-flop causes T1 to conduct and act as a short circuit across the external capacitor. For that reason, the capacitor cannot charge. During that time, the input to the upper comparator is near zero volts causing the comparator output to keep the control flip-flop reset.



ASTABLE OPERATION

The other basic operational mode of the 555 is as astable multivibrator. An astable multivibrator is simply an oscillator. The astable multivibrator generates a continuous stream of rectangular off-on pulses that switch between two voltage levels. The frequency of the pulses and their duty cycle are dependent upon the RC network values.

Fig shows the 555 connected as an astable multivibrator. Both the trigger and threshold inputs to the two comparators are connected together and to the external capacitor. The capacitor charges toward the supply voltage through the two resistors, R1 and R2. The discharge pin (7) connected to the internal transistor is connected to the junction of those two resistors. When power is first applied to the circuit, the capacitor will be uncharged; therefore, both the trigger and threshold inputs will be near zero volts. The lower comparator sets the control flip-flop causing the output to switch high. That also turns off transistor T1. That allows the capacitor to begin charging through R1 and R2. As soon as the charge on the capacitor reaches 2/3 of the supply voltage, the upper comparator will trigger causing the flip-flop to reset. That causes the output to switch low. Transistor T1 also conducts. The effect of T1 conducting causes resistor R2 to be connected across the external capacitor. Resistor R2 is effectively connected to ground through internal transistor T1. The result of that is that the capacitor now begins to discharge through R2.The voltage across the capacitor reaches 1/3 of the supply voltage, the lower comparator is triggered. The control flip-flop to set and the output to go high.T1 cuts off and again the capacitor begins to charge. The cycle continues to repeat with the capacitor alternately charging



and discharging, as the comparators cause the flip-flop to be repeatedly set and reset. The resulting output is a continuous stream of rectangular pulses.The frequency of operation of the astable circuit is dependent upon the values of R1, R2, and C. The frequency can be calculated with the formula:

f = 1/ (.693 x C x (R1 + 2 x R2))

The Frequency f is in Hz, R1 and R2 are in ohms, and C is in farads. The time duration between pulses is known as the 'period', and usually designated with a’t’. The pulse is on for t1 seconds, then off for t2 seconds. The total period (t) is t1 + t2 .

The time intervals for the on and off portions of the output depend upon the values of R1 and R2. The ratio of the time duration when the output pulse is high to the total period is known as the duty-cycle. The duty-cycle can be calculated with the formula:

D = t1/t = (R1 + R2) / (R1 + 2R2)You can calculate t1 and t2 times with the formulas below:

t1 = .693(R1+R2)Ct2 = .693 x R2 x C

The 555 can produce duty-cycles in the range of approximately 55 to 95%. A duty-cycle of 80% means that the output pulse is on or high for 80% of the total period.



6.2 IR LIGHT EMITTING DIODES (LEDs):

Function: IR LEDs emit infrared light when forward biased.

Circuit symbol:

There are a couple key differences in the electrical characteristics of infrared LEDs versus visible light LEDs. Infrared LEDs have a lower forward voltage, and a higher rated current compared to visible LEDs. This is due to differences in the material properties of the junction. A typical drive current for an infrared LED can be as high as 50 milliamps, so dropping in a visible LED as a replacement for an infrared LED could be a problem with some circuit designs.

THERMAL RUN-AWAY

When a junction gets warmer, the current through it at a given voltage will increase. The increased current in turn heats the junction further, and the problem gets worse. Eventually, if nothing limits the current, the junction will fail due to the heat. Because of thermal runaway, it’s important to use some current limiting circuit even with a regulated voltage source.



6.3 IR SENSOR TSOP 1738

A sensor is a type of transducer, or mechanism that responds to a type of energy by producing another type of energy signal, usually electrical. They are either direct indicating (an electrical meter) or are paired with an indicator (perhaps indirectly through an analog to digital converter, a computer and a display) so that the value sensed is translated for human understanding. Types of sensors include electromagnetic, chemical, biological and acoustic.

In order to act as an effectual sensor, the following guidelines must be met: The sensor should be sensitive to the measured property.

The sensor should be insensitive to any other property. The sensor should not influence the measured property.

Features of IR SENSOR used: Photo detector and preamplifier circuit in the same casing.

Receives and amplifies the infrared signal without any external component.

38 kHz integrated oscillator.

High sensitivity.

High level of immunity to ambient light.

Improved shielding against electrical field interference.

TTL and CMOS compatibility.



6.4 RELAY

A relay is an electrical switch that opens and closes under control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. These contacts can be either Normally Open (NO), Normally Closed (NC), or change-over contacts.

Normally-open contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called Form A contact or "make" contact. Form A contact is ideal for applications that require to switch a high-current power source from a remote device.

Normally-closed contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called Form B contact or "break" contact. Form B contact is ideal for applications that require the circuit to remain closed until the relay is activated.

Change-over contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called Form C contact

OPERATION

When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current to the coil is switched off, the armature is returned by a force that is half as strong as the magnetic force to its relaxed position. The magnetic flux in the armature induces a current in opposition to the current provided to the coil called 'back emf'. There is a rush of current to operate the coil and move the contacts, but once the armature is closed, the current required to hold the armature closed is a small fraction of that, typically a tenth. Relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.



6.5 SOLENOIDS

A solenoid is a loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electrical current is passed through it. Solenoids are important because they can create controlled magnetic fields and can be used as electromagnets. The term is also often used to refer to a solenoid valve, which is an integrated device containing an electromechanical solenoid which actuates either a pneumatic or hydraulic valve.

FUNCTION:

Solenoid used in the circuit lifts up the valve fitted in the pipe to let water flow out of the tap .Solenoids valves are used specifically for this purpose .

Solenoid valves are devices that use a solenoid to control valve activation. Actuation methods include electric, electro-hydraulic, electro pneumatic, and pneumatic. Unpowered states include normally open and normally closed. In a tandem center solenoid valve, the pressure and tank ports are connected while the service ports are blanked. This allows system unloading while still providing isolation of the service lines. In a float center solenoid valve, the supply pressure port is closed. All others ports are interconnected. This allows the supply to be shut off while enabling the load to move or free wheel with flow available to other services.



6.6 RESISTORS

Function: Resistors restrict the flow of electric current, for example a resistor is placed in series with a light-emitting diode (LED) to limit the current passing through the LED.

Circuit symbol:

POWER RATING OF RESISTORS

Electrical energy is converted to heat when current flows through a resistor. Usually the effect is negligible, but if the resistance is low (or the voltage across the resistor high) a large current may pass making the resistor become noticeably warm. The resistor must be able to withstand the heating effect and resistors have power ratings to show this.

6.7 FREE-WHEELING DIODE

A two-terminal semiconductor (rectifying) device that exhibits a nonlinear current-voltage characteristic. The function of a diode is to allow current in one direction and to block current in the opposite direction. The terminals of a diode are called the anode and cathode.

Function: In the circuit diode protects the relay from damage by high voltages generated by back emf when the relay is de-energized.

6.8 CAPACITOR

A capacitor is a device that stores an electrical charge or energy on it's plates. These plates, a positive and a negative plate, are placed very close together with an insulator in between to prevent the plates from touching each other. A capacitor can carry a voltage equal to the battery or input voltage.



6.9 TRANSISTORS

Transistors fall into the category of bipolar transistor, either the more common NPN bipolar transistors or the less common PNP transistor types. There is a further type known as a FET transistor which is an inherently high input impedance transistor with behavior somewhat comparable to valves.

Function: Transistors work on the principle that certain materials e.g. silicon, can after processing be made to perform as "solid state" devices. Any material is only conductive in proportion to the number of "free" electrons that are available. Silicon crystals for example have very few free electrons. However if "impurities" (different atomic structure - e.g. arsenic) are introduced in a controlled manner then the free electrons or conductivity is increased. By adding other impurities such as gallium, an electron deficiency or hole is created. As with free electrons, the holes also encourage conductivity and the material is called a semi-conductor.

In the circuit NPN transistor (T1) BC548 is used to drive the IR LED and (T2) BC548 is used to drive the relay(RL1) .



CHAPTER 7

WORKING7.1 Transmitter7.2 Receiver



WORKING

The circuit comprises a transmitter and a receiver, both are built around 555 timer. The IR rays continuously emitted by the transmitter fall on the receiver. As soon as an obstacle comes in between the receiver and the transmitter, interrupting the IR rays, the output of the IR rays sensor goes momentarily low to trigger the timer circuit in the receiver and water comes out for 11 seconds through the tap.

7.1 TRANSMITTER

It is built around timer IC 555 which is used as an astable multivibrator to generate around 38 kHz of frequency .The timer output is fed to transistor T 1 which drives the IR LED (LED 1).Its transmission wavelength of 900- 1100 nm lies in the peak receptivity range of TSOP1738 receiver module.



7.2 RECEIVER

It comprises the sensor module, monostable timer and relay driver circuit. The sensor module TSOP1738 is sensitive to IR radiation modulated at 38 kHz. Its normally high output goes momentarily low when any IR radiation detected or interrupted, it triggers the timer IC 555 (IC2). The output of timer goes high for 11 seconds and relay drives the solenoid .During this time period, energization of solenoid lifts up the valve fitted in the pipe to let water flow out of the tap.

The relay driver circuit consists of resistor R8, transistor BC548 (T2) and free-wheeling diode D1. Diode protects the relay from damage by high voltages generated by the back emf when the relay is de- energized.

The time period for which the timer goes high can be calculated as follows Ton = 1.1 R6 C5

= 1.1 * 100 * 103 * 100 * 10-6 = 11 seconds

When we put our hands between IR LED and IR sensor, the relay energizes to make the solenoid open up the valve and water flows out of the tap.



CHAPTER 8

APPLICATIONS



APPLICATIONS

The design objective has been fulfilled and the system is showing proper output. For future work, the circuit can be used as a subsystem in circuits where automatic control of various mechanical instruments is required by using electronic circuit.

The circuit was designed keeping in mind the automatic control of various mechanical devices by using electronic circuit’s .Thus trying to signify the applications of electronics and instrumentation. By adding timer to the circuit enhance the idea and operate the device in a more broader sense.

This circuit finds wide applications in our daily life. This circuit is not only used for automatically controlling the tap of wash-basin but it can be used for controlling the dryers ,blowers and door opening and closing by replacing the solenoid.

The key learning of the project is to understand the basic working of the IC 555 timer, in monostable and astable mode and IR TSOP1738 sensor.



CHAPTER 9

APPENDIX9.1 Datasheet of IC 555 Timer9.2 Datasheet of IR LED9.3 Datasheet of IR Sensor TSOP 17389.4 Datasheet of Relay9.5 Datasheet of Free Wheeling Diode9.6 Datasheet of Transistor BC548



APPENDIX

9.1 Datasheet of IC 555 Timer

















9.2 DATASHEET OF IR LED









9.3 Datasheet of IR Sensor TSOP 1738









9.4 Datasheet of Free Wheeling Diode







9.5 Datasheet of Transistor BC548







BIBLIOGRAPHY



BIBLIOGRAPHY

Op-Amps and linear integrated circuits by Ramakant A. Gayakwad.

Power Electronics- Dr. P.S. Bimbhara

Electronic devices and circuit theory – Boylestad and Nashelsky

Internet Sites:

www.google.com

www.wikepidia.com

www.msnencarta.com

www.howstuffworks.com


http://www.howstuffworks.com/

http://www.msnencarta.com/

http://www.wikepidia.com/

http://www.google.com/

Automatic IR Tap Controller

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