Kendriya

Vidyalay

aB.S.F

.

Camp

Chhawla

Physics

Project

Work 201

4-201

5

Year

Made By: Dhananjay Kumar

Class: XIIth Science

Roll No. : 2

Automatic Street Light System Using Light Dependent Resistor

Automatic street light system is very common nowadays as it provides intelligent street lighting mechanism. It provides light automatically during night without any human interference. These energy saving street lights make use of incandescent lamps instead of LEDs. So here I will teach you how to make an electronic circuit for street light automation. The heart of this circuit is a LDR (Light Depended Resistor) which is connected as a potential divider with a 56K resistor. The drop across LDR is used for switching the transistor. Solar led street lighting systems are the advanced versions of this ordinary automatic street light controller.Working of Automatic Street Light System

The bulb should remain OFF during daytime and turn ON automatically during night.The unique property of light depended resistor is utilized here. LDR is a variable resistor which has very low resistance in the presence of light and very high resistance in the absence of light.In this circuit, we create a potential divider network with an ordinary resistor in one arm and a LDR on the other arm.According to Ohm’s law (V=IR), voltage drop across the resistor increases when its resistance increases.Here the drop across LDR varies with changes in light intensity. That is voltage drop across the LDR is minimum in the presence of light and maximum in the absence of light.

One end of the LDR is connected to the base of a BC 187 transistor. At night, the drop is very high (> 0.6V) and it is sufficient to turn on the transistor.When the first transistor is ON next one will also turn ON. Thus the relay coil energizes and the bulb will glow.

Components Used:1. LDR (Light Dependent Resistor)2. Resistances3. Led Bulbs4. Transformer 1A5. Relay 6V6. Diode N40017. Transistor

About Components:1. LDR (Light Dependent Resistor)

A light-dependent resistor (LDR) or photocell is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity; in other words, it exhibits photoconductivity. A photoresistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits.A photoresistor is made of a high resistance semiconductor. In the dark, a photoresistor can have a resistance as high as a few megaohms (MΩ), while in the light, a photoresistor can have a resistance as low as a few hundred ohms. If incident light on a photoresistor exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons (and their hole partners) conduct electricity, thereby lowering resistance. The resistance range and sensitivity of a photoresistor can substantially differ among dissimilar devices. Moreover, unique photoresistors may react substantially differently to photons within

certain wavelength bands.A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (that is, longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor.

Specification and Model:There are many types of photoresistors, with different specifications and models. Photoresistors can be coated with or packaged in different materials that vary the resistance, depending on the use for each LDR.

Application:Photoresistors come in many types. Inexpensive cadmium sulphide cells can be found in many consumer items such as camera light meters, street lights, clock radios, alarm devices, night lights, outdoor clocks, solar street lamps and solar road studs, etc.They are also used in some dynamic compressors together with a small incandescent lamp or light-emitting diode to control gain reduction. The use of CdS and CdSe photoresistors is severely restricted in Europe due to the RoHS ban on cadmium. Lead sulphide (PbS) and indium antimonide (InSb) LDRs (light-dependent resistors) are used for the mid-infrared spectral region.

Ge: Cu photoconductors are among the best far-infrared detectors available, and are used for infrared astronomy and infrared spectroscopy.

2.ResistancesA resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage levels within circuits. Resistors may have fixed resistances or variable resistances, such as those found in thermistors, varistors, trimmers, photoresistors, humistors, piezoresistors and potentiometers.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This relationship is represented by Ohm's law:

where I is the current through the conductor in units of amperes, V is the potential difference measured across

the conductor in units of volts, and R is the resistance of the conductor in units of ohms (symbol: Ω).

Units:The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of values, the derived units of milliohm (1 mΩ = 10−3 Ω), kilohm (1 kΩ = 103 Ω), and megaohms (1 MΩ = 106 Ω) are also in common usage.The reciprocal of resistance R is called conductance G = 1/R and is measured in Siemens (SI unit), sometimes referred to as a mho. Hence, Siemens is the reciprocal of an ohm: . Although the concept of conductance is often used in circuit analysis, practical resistors are always specified in terms of their resistance (ohms) rather than conductance.

Electronic Symbol and Notations:The symbol used for a resistor in a circuit diagram varies from standard to standard and country to country. Two typical symbols are as follows;

American-style symbols. (a) Resistor, (b) rheostat (variable resistor), and (c) potentiometer

 

IEC-style resistor symbolThe notation to state a resistor's value in a circuit diagram varies, too. The European notation avoids using a decimal separator, and replaces the decimal separator with the SI prefix symbol for the particular value. For example, 8k2 in a circuit diagram indicates a resistor value of 8.2 kΩ. Additional zeros imply tighter tolerance, for example 15M0. When the value can be expressed without the need for an SI prefix, an 'R' is used instead of the decimal separator. For example, 1R2 indicates 1.2 Ω, and 18R indicates 18 Ω. The use of a SI prefix symbol or the letter 'R' circumvents the problem that decimal separators tend to 'disappear' when photocopying a printed circuit diagram.

3.Led BulbsA light-emitting diode (LED) is a two-lead semiconductor light source that resembles a basic pn-junction diode, except that an LED also emits light. When an LED's anode lead has a voltage that is more positive than its cathode lead by at least the LED's forward voltage drop, current flows. Electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor.An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern.

4.TransformerA transformer is an electrical device that transfers energy between two or more circuits through electromagnetic induction. A varying current in the transformer's primary winding creates a varying magnetic flux in the core and a varying magnetic field impinging on the secondary winding. This varying magnetic field at the secondary induces a varying electromotive force (emf) or voltage in the secondary winding. Making use of Faraday's Law in conjunction with high magnetic permeability core properties, transformers can thus be designed to efficiently change AC voltages from one voltage level to another within power networks. Transformers range in size from RF transformers a small fraction of a cm3 in volume to units interconnecting the power grid weighing hundreds of tons. A wide range of transformer designs are used in electronic and electric power applications. Transformers are essential for the transmission, distribution, and utilization of electrical energy.

5.RelayA relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating

characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

6.DiodeIn electronics, a diode is a two-terminal electronic component with asymmetric conductance; it has low (ideally zero) resistance to current in one direction, and high (ideally infinite) resistance in the other. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals.[5] A vacuum tube diode has two electrodes, a plate (anode) and a heated cathode. Semiconductor diodes were the first semiconductor electronic devices. The discovery of crystals’ rectifying abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor diodes, called cat's whisker diodes, developed around 1906, were made of mineral crystals such as galena. Today, most diodes are made of silicon, but other semiconductors such as selenium or germanium are sometimes used.

7.Transistor

A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the

transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.