27-06-2014, 12:22 PM
Automatic Street Light Controller Using LDR
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1. Introduction
Automatic Street Light Control System is a simple and powerful concept, which uses transistor as a switch to switch ON and OFF the street light automatically. By using this system manual works are removed. It automatically switches ON lights when the sunlight goes below the visible region of our eyes. It automatically switches OFF lights under illumination by sunlight. This is done by a sensor called Light Dependant Resistor (LDR) which senses the light actually like our eyes.
By using this system energy consumption is also reduced because now-a-days the manually operated street lights are not switched off properly even the sunlight comes and also not switched on earlier before sunset. In sunny and rainy days, ON time and OFF time differ significantly which is one of the major disadvantage of using timer circuits or manual operation.
This project exploits the working of a transistor in saturation region and cut-off region to switch ON and switch OFF the lights at appropriate time with the help of an electromagnetically operated switch.
Automatic Streetlight needs no manual operation of switching ON and OFF. The system itself detects whether there is need for light or not. When darkness rises to a certain value then automatically streetlight is switched ON and when there is other source of light, the street light gets OFF. The extent of darkness at which the street light to be switched on can also be tailored using the potentiometer provided in the circuit.
. Principle
The automatic streetlight control system operates on 12 V DC supply. The automatic streetlight controller has a photoconductive device whose resistance changes proportional to the extent of illumination, which switches ON or OFF the LED with the use of transistor as a switch
.
Light dependent resistor, a photoconductive device has been used as the transducer to convert light energy into electrical energy. The central dogma of the circuit is that the change in voltage drop across the light dependent resistor on illumination or darkness switches the transistor between cut-off region or saturation region and switches OFF or ON the LED.
1 Diode
A diode is a two-terminal electronic component that conducts electric current in only one direction. A semiconductor diode is a crystalline piece of semiconductor material connected to two electrical terminals. A vacuum tube diode is a vacuum tube with two electrodes: a plate and a cathode.
The most common function of a diode is to allow an electric current to pass in one direction while blocking current in the opposite direction. Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current and to extract modulation from radio signals in radio receivers.
When p-type and n-type materials are placed in contact with each other, the junction is depleted of charge carriers and behaves very differently than either type of material. The electrons in n-type material diffuse across the junction and combines with holes in p-type material. The region of the p-type material near the junction takes on a net negative charge because of the electrons attracted. Since electrons departed the N-type region, it takes on a localized positive charge. The thin layer of the crystal lattice between these charges has been depleted of majority carriers, thus, is known as the depletion region. It becomes nonconductive intrinsic semiconductor material. This separation of charges at the p-n junction constitutes a potential barrier, which must be overcome by an external voltage source to make the junction conduct.
The electric field created by the space charge region opposes the diffusion process for both electrons and holes. There are two concurrent phenomena: the diffusion process that tends to generate more space charge and the electric field generated by the space charge that tends to counteract the diffusion
2 Transistor as an Amplifier
A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. To be more specific, the current applied to the base terminal will be multiplied by the current gain factor of the transistor which known as hFE. Therefore transistor can be used as amplifier. Any small signal applied to the base terminal will be amplified by the factor of hFE and reflected as a collector current on the collector terminal side.
When we operate transistor as an amplifier, we choose the bias voltage VBE and VCE in such a way that the output IC and VCE will swing to maximum value (saturation region) or minimum value (cut-off region) without any distortion when the input IB swing to its maximum or minimum value.
Uses of this project
By employing this circuit, energy consumption can be reduced considerably as the light switches ON or OFF automatically in appropriate time. Moreover, errors which occur due to manual operation also can be eliminated completely. The Automatic street light controller unit fabrication is cost-effective with good sensitivity and high reproducibility. Moreover, the construction of the circuit is also simple so that it can be done easily as it involves locally available components. The circuit is designed in such a way that the extent of darkness at which the light has to switch ON or OFF also can be tailored whenever it is needed. It can be used for other purposes like garden lighting, balcony lighting etc.,
[attachment=65409]
1. Introduction
Automatic Street Light Control System is a simple and powerful concept, which uses transistor as a switch to switch ON and OFF the street light automatically. By using this system manual works are removed. It automatically switches ON lights when the sunlight goes below the visible region of our eyes. It automatically switches OFF lights under illumination by sunlight. This is done by a sensor called Light Dependant Resistor (LDR) which senses the light actually like our eyes.
By using this system energy consumption is also reduced because now-a-days the manually operated street lights are not switched off properly even the sunlight comes and also not switched on earlier before sunset. In sunny and rainy days, ON time and OFF time differ significantly which is one of the major disadvantage of using timer circuits or manual operation.
This project exploits the working of a transistor in saturation region and cut-off region to switch ON and switch OFF the lights at appropriate time with the help of an electromagnetically operated switch.
Automatic Streetlight needs no manual operation of switching ON and OFF. The system itself detects whether there is need for light or not. When darkness rises to a certain value then automatically streetlight is switched ON and when there is other source of light, the street light gets OFF. The extent of darkness at which the street light to be switched on can also be tailored using the potentiometer provided in the circuit.
. Principle
The automatic streetlight control system operates on 12 V DC supply. The automatic streetlight controller has a photoconductive device whose resistance changes proportional to the extent of illumination, which switches ON or OFF the LED with the use of transistor as a switch
.
Light dependent resistor, a photoconductive device has been used as the transducer to convert light energy into electrical energy. The central dogma of the circuit is that the change in voltage drop across the light dependent resistor on illumination or darkness switches the transistor between cut-off region or saturation region and switches OFF or ON the LED.
1 Diode
A diode is a two-terminal electronic component that conducts electric current in only one direction. A semiconductor diode is a crystalline piece of semiconductor material connected to two electrical terminals. A vacuum tube diode is a vacuum tube with two electrodes: a plate and a cathode.
The most common function of a diode is to allow an electric current to pass in one direction while blocking current in the opposite direction. Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current and to extract modulation from radio signals in radio receivers.
When p-type and n-type materials are placed in contact with each other, the junction is depleted of charge carriers and behaves very differently than either type of material. The electrons in n-type material diffuse across the junction and combines with holes in p-type material. The region of the p-type material near the junction takes on a net negative charge because of the electrons attracted. Since electrons departed the N-type region, it takes on a localized positive charge. The thin layer of the crystal lattice between these charges has been depleted of majority carriers, thus, is known as the depletion region. It becomes nonconductive intrinsic semiconductor material. This separation of charges at the p-n junction constitutes a potential barrier, which must be overcome by an external voltage source to make the junction conduct.
The electric field created by the space charge region opposes the diffusion process for both electrons and holes. There are two concurrent phenomena: the diffusion process that tends to generate more space charge and the electric field generated by the space charge that tends to counteract the diffusion
2 Transistor as an Amplifier
A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. To be more specific, the current applied to the base terminal will be multiplied by the current gain factor of the transistor which known as hFE. Therefore transistor can be used as amplifier. Any small signal applied to the base terminal will be amplified by the factor of hFE and reflected as a collector current on the collector terminal side.
When we operate transistor as an amplifier, we choose the bias voltage VBE and VCE in such a way that the output IC and VCE will swing to maximum value (saturation region) or minimum value (cut-off region) without any distortion when the input IB swing to its maximum or minimum value.
Uses of this project
By employing this circuit, energy consumption can be reduced considerably as the light switches ON or OFF automatically in appropriate time. Moreover, errors which occur due to manual operation also can be eliminated completely. The Automatic street light controller unit fabrication is cost-effective with good sensitivity and high reproducibility. Moreover, the construction of the circuit is also simple so that it can be done easily as it involves locally available components. The circuit is designed in such a way that the extent of darkness at which the light has to switch ON or OFF also can be tailored whenever it is needed. It can be used for other purposes like garden lighting, balcony lighting etc.,