Automatic Street Light Control System (Sensor using LDR & Transistor BC 547)

Briefing:

Her is our new simple Electrical/ Electronics project about Automatic Street Light Control System. Itis a simple and powerful concept, which uses transistor (BC 547 NPN) as a switch to switch ON and OFF the street light system automatically. It automatically switches ON lights when the sunlight goes below the visible region of our eyes.(e.g in evening after Sunset). It automatically switches OFF lights when Sunlight fall on it ( i.e on LDR )e.g in morning, by using a sensor calledLDR(Light Dependent Resistor) which senses the light just like our eyes.Advantages:

By using this Automatic system for street light controlling, we can reduce energy consumption because 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, ONand OFF time differnoticeablywhich is one of the major disadvantage of using timer circuits or manual operation for switching the street light system.

Requirements LDR Light Dependent Resistor Take 2 transistors. (NPN transistor- BC547 or BC147 or BC548) Resistor- 1K, 330Ohm, 470 ohm Light emitting diode (LED) - Any color Connecting wires- Use single-core plastic-coated wire of 0.6mm diameter (the standard size)-You can use wire that is used for ComputerNetworking. Power supply-6V or 9V

Procedure Insert first transistor Q1-BC547 (NPN)on breadboard (or general PCB) as shown in the circuit diagram 1. Connectanother transistor Q2- BC547 (NPN) on breadboard as in step 1. Connect wires across emitter pin of both transistors and ve terminal of battery (lowest/ bottom rowof breadboard.) Connecta wire across Collector pin of transistor Q1 and Base pin of transistor Q2. Connecta resistor 1K across positive terminal of battery (topmost row of breadboard) and Collector pin of transistor Q1. ConnectLight Dependent Resistor (LDR) across positive terminal of battery (topmost row of breadboard) and base terminal of transistor Q1. insert a resistor- 330 Ohm across base pin of transistor Q1 and negative terminal of battery (lowest bottom row of breadboard). Connect a resistor 330R acrosspositive terminal of battery (topmost row of breadboard) and anode terminal of LED (Light emitting diode) & Connect the cathode terminal of LED to Collector pin of transistor Q2.

The simple circuit is ready for testing now. Connect 6V battery terminals to the circuit as show infigand see the output. As you block light falling onLight dependent resistor(LDR), the LED glows.

LED GLOWS EVEN IN LESS DARKNESS. Use torch light or Lighterif the LED glows in less darkness. in addition, you can try to adjust the sensitivity of thiscircuit by using a variable resistor in place of R1-300Ohm. Try this circuit with other resistances as well, (e.g, 1K, 10Kand 100K, etc)

Requirements:

Circuit Diagram 1.Automatic Street Light Control System.(Sensor using LDR & Transistor BC 547.) Very Simple. We have tried this one in thistutorialbu you can also try the second one

Circuit Diagram 2.Automatic Street Light Control System.(Sensor using LDR & Transistor BC 547.) Very Simple.

As Light is falling on LDR ( Light Dependent resistor) So LEDdoes not glow. ( LED = Off) ImageTaken Our from Video

You can see now that we have blocked light falling onLight dependent resistor(LDR), so the LED glows( LED = ON) ImageTaken Out from Video

WHAT IS LDR?

Aphoto resistororlight-dependent resistor(LDR) orphotocellis a light-controlled variableresistor. Theresistanceof a photo resistor decreases with increasing incident light intensity; in other words, it exhibitsphotoconductivity. A photo resistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits.A photo resistor is made of a high resistancesemiconductor. In the dark, a photo resistor can have a resistance as high as a few mega ohms (M), while in the light, a photo resistor can have a resistance as low as a few hundred ohms. If incident light on a photo resistor exceeds a certainfrequency,photonsabsorbed by the semiconductor give boundelectronsenough energy to jump into theconduction band. The resulting free electrons (and itsholepartners) conduct electricity, thereby lowering resistance. The resistance range and sensitivity of a photo resistor can substantially differ among dissimilar devices. Moreover, unique photo resistors may react substantially differently to photons within certain wavelength bands.A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its owncharge carriersand is not an efficient semiconductor, for example, silicon. In intrinsic devices the only available electrons are in thevalence band, and hence the photon must have enough energy to excite the electron across the entireband gap. Extrinsic devices have impurities, also calleddo-pants, 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.

Figure 1 Figure 2

Figure 1: The symbol for a photo resistorFigure 2: The internal components of a photoelectric control for a typical American streetlight. The photo resistor is facing rightwards, and controls whether current flows through the heater which opens the main power contacts. At night, the heater cools, closing the power contacts, energizing the street light.

Figure: DEPENDANT RESISTOR