ABSTRACT
As everyone is aware that the entire globe is undergoing power crisis, it is now time to invent energy saving devices. One such device is "Automatic Street Light Controller".Currently the Street lights are manually operated which is human dependent. This leads to in-effective operation which in turn consumes large amount of power. Thus by introducing this automatic street light controller the switching off is totally eliminated and hence the power is consumed only when it is required (during the night time).
In this automatic street light controller, Light Dependent Resistors (LDR) are used for the purpose of switching on the light when there is no other means of light and Switching off automatically when there is other source of light present. This is a cost effective and user friendly mechanism.
INTRODUCTION
Automatic Streetlight controller needs no manual operation for switching ON and OFF when there is need of light. It detects itself 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 i.e. day time, the street light gets OFF. The sensitiveness of the street light canal has to be adjusted. In our project we have used L.E.D for indication of bulb but for high power switching one can connect relay (electromagnetic switch). Then it will be possible to turn ON/OFF any electrical appliances connected all the way through relay.CIRCUIT WORKING:
This inexpensive unit switches the light ON at night and OFF again at day. The circuit has separate time bases for the ON and OFF delays. The voltage at junction R1-LDR-C1 is inversely proportional to the light intensity measured by light dependent resistor LDR. Switch trigger gate N1 toggles whenever this voltage reaches one of the input threshold levels. Since the difference between these levels is large compared with the voltage span produced by the potential divider, a variable feedback loop is provided to achieve effective switching span of 300 to 400mV.
When the output of N1 is high, the voltage at junction R2-PR1 is almost equal to the supply voltage. When the output is low, the voltage drops to the level required for the threshold difference as the input on N1.
The output of N1 drives two time base circuit C2-R5-D1 for the ON state and C2-R6-D2 for the OFF state. These networks switch the output of N2 ON and OFF after the wanted delays. The lamp relay and an indication LED are driven by Darlington stage T1-T2, which is controlled by the output of N2.
Capacitor C1 prevents HF signals picked up by the cable between the LDR and the switching unit causing superiors triggering. Because of the high output impedance of the type 4093, the cable should be a screened type.
The remaining two gates in the 4093 package may be used for duplicating the time base to obtain a switching sequence. The values shown for R6-C2 and R5-C2 from a good starting point for dimensioning the delays introduced in this additional time base.
The lowest permissible value of R5 and R6 is 47KE their highest value depends mainly on the leakage current of C2.
During the testing of photo types of this circuit, it was noted that the switching threshold and hysteresis depend on the make of the 4093. Good results were obtained with SGS’s HCF4093BE devices from other manufacturers may require the value of R3 to be slightly different. The inputs of the unused gates in the 4093 must be earthed.
The LDR is mounted in a suitable waterproof housing, screened from direct light sources.
Preset PR1 serves to adjust the light intensity level at which the circuit switches. To prevent too slow response to changes in the setting the timer should be aligned with SW1 open. The current drawn by the timer is mainly that drawn by the energized relay.
COMPONENTS
A. LDR:
A photo resistor or light dependent resistor (LDR) is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor. A photo resistor is made of a high resistance semiconductor.
The main purpose of a light dependent resistor is to change the brightness of a light in different weather conditions. This can easily be explained with the use of a watch. Some watches start to glow in the dark so that it is possible to see the time without having to press any buttons. It is the light dependent resistor that allows the watch to know when it has gotten dark, and change the emissions level of the light at that time. Traffic lights use this principle as well but their lights have to be brighter in the day time.
B. LED:
A LED is short form of Light Emitting Diode. It is used extensively as indicator lights on all sorts of electronic devices. An LED always emits colored light, usually red, green, yellow or orange. Blue LEDs are very rare and expensive. LEDs can have all sorts of shapes but the most common ones are cylindrical with rounded fronts and are 3 to 5 mm in diameter. Other types of LEDs emit very bright light. One example of this type of LED is the Infrared LED or IR-LED. These emit invisible infrared light and are widely used in remote controls.The LED has two terminals, the Anode is the positive terminal and the Cathode is the negative terminal. Figure below shows the schematic symbol of a LED. In photo 1 a red LED is shown. The longest one of the terminals is always the Anode.
LED Schematic symbol
LED
C. RELAY
A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open.
D. IC CD4093
E. PCB(Printed Circuit Board)
With the help of P.C.B it is easy to assemble circuit with neat and clean end products. P.C.B is made of Bakelite with surface pasted with copper track-layout. For each components leg, hole is made. Connection pin is passed through the hole and is soldered.F. Transistor
Transistors BC 141 & BC 107 types are used in this automatic street light controller. These transistors act as a driving circuit for the working of the relay which in turn connected to the street light.Advantages
- The circuit is simple and can be assembled on a small general – purpose PCB .
- Makes sure that LDR and the light bulb are well separated.
