In this project, we are avoiding the problem by having an automatic system which turns ON and OFF the lights at given time or when the ambient light falls below a specific intensity. Each controller has an LDR which is used to detect the ambient light. If the ambient light is below a specific value the lights are turned ON. A light dependent sensor is interfaced to the AVR microcontroller it is used to track the sunlight and when the sensors goes dark the led will be made ON and when the sensors found light the led will be made OFF.
It clearly demonstrates the working of transistor in saturation region and cut-off region. The working of relay is also known microcontroller and the code is written in C language in AVR programmer. Automatic light control is a simple yet powerful concept, which uses transistor as a switch. The aim of this project is to control the light using LDR.
When the light falling occur means resistance value will be change. There is no light then the resistance value is change. AVR is stand for peripheral interface controller. When the light is available then it will be in the OFF state and when it is dark the light will be in ON state, it means LDR is inversely proportional to light.
All this command are sent to the controller then according to that the device operates. Normally the resistance of an LDR is very high, sometimes as high as ohms, but when they are illuminated with light resistance drops dramatically. The best-known devices of this type are the light dependent resistor LDR , the photo diode and the phototransistors.
Light dependent resistors as the name suggests depend on light for the variation of resistance. The longer the strip the more the value of resistance. In the absence of light the resistance can be in the order of 10K ohm to 15K ohm and is called the dark resistance.
Depending on the exposure of light the resistance can fall down to value of ohms. The power ratings are usually smaller and are in the range 50mW to 0.
Though very sensitive to light, the switching time is very high and hence cannot be used for high frequency applications. They are used in chopper amplifiers.
Light dependent resistors are available as disc 0. The resistance rises to several Mega ohms under dark conditions. The below figure shows that when the torch is turned on, the resistance of the LDR falls, allowing current to pass through it is shown in figure.
The basic construction and symbol for LDR are shown in above figures respectively. The device consists of a pair of metal film contacts separated by a snakelike track of cadmium sulphide film, designed to provide the maximum possible contact area with the two metal films. Practical LDRs are available in variety of sizes and packages styles, the most popular size having a face diameter of roughly 10mm.
The recovery rate is specified does not increase immediately to the dark value. The recovery rate is much greater in the reverse direction, e. A LDR may be connected either way round and no special precautions are required when soldering. The LDR is a variable resistor whose resistance decreases with the increase in light intensity.
Two cadmium sulphide cds photoconductive cells with spectral response similar to that of the human eye. The cell resistance falls with increasing light intensity. Another V power supply connected to the load. To make a 5V Dc regulated power supply we connected a voltage regulator which give the power supply to the ATmega8 microcontroller and peripheral items.
Two led is also interface to show the status of the power. The 12V adapter image shown in below figure. To make a 5volt power supply, IC voltage regulator as shown in figure has been used. The IC is simple to use.
Simply connect the positive lead form unregulated DC power supply anything from 9VDC to 12VDC to the input pin, connect the negative lead to the common pin and then turn on the power, a 5 volt supply from the output pin will be gotten.
Here the operating conditions of the transistor are zero input base current IB , zero output collector current IC and maximum collector voltage VCE which results in a large depletion layer and no current flowing through the device. When the transistor will be biased so that the maximum amount of base current is applied, resulting in maximum collector current resulting in the minimum collector emitter voltage drop which results in the depletion layer being as small as possible and maximum current flowing through the transistor.
Resistors act to reduce current flow, and, at the same time, act to lower voltage levels within circuits. The current through a resistor is in direct proportion to the voltage across the resistor's terminals.
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors can be composed of various compounds and films, as well as resistance wires wire made of a high-resistivity alloy, such as nickel-chrome.
Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits. The electrical functionality of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application.
The temperature coefficient of the resistance may also be of concern in some precision applications. Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinks. In a high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor.
While there is no minimum working voltage for a given resistor, failure to account for a resistor's maximum rating may cause the resistor to incinerate when current is run through it. To calculate a four band resistor value, use the middle four "drop" boxes then click on the "Calc 4 Band" button.
For a five or six band resistor, you can use all six boxes but all 6 do not necessarily have to be used - the "Temperature Coefficient" box, for example. After you have selected the 6 "drop box" choices, remember to click the "Calc 5 Band" button for your answer. If you have calculated a 5 or 6 band resistor, and go back to calculating a 4 band resistor, the two drop boxes on the ends far left and far right will not clear but this is perfectly all right.
For larger values, kilo ohms 1, ohms and mega ohms 1,, ohms are used. For example 3, ohms equals 3. Color "bands" are used to indicate the resistance value with each color signifying a number and these color bands are grouped closer to one end of the resistor than the other.
The third color band is the multiplier of the first 2 bands. Here, black is 1, brown is 10, red is and so on. Putting this in other words, the value of the third band the multiplier is the number 10 raised to the power of the color code. The 4th band is the resistor's tolerance and shows how precisely the resistor was manufactured.
Now that we know the values of each color, let's try calculating a few examples of resistance values. Looking at resistor 1, we see the colors red red green gold. Use the 5 Band Chart to solve these next problems.
For resistor 4, we see the first 3 bands are violet, green and red which "translate" into 7, 5 and 2. Looking at the fourth band the multiplier ; we see it is brown and has a value of Band 5 is red which indicates a 2 per cent tolerance and a brown sixth band means that the temperature coefficient is parts per million ppm.
Examining resistor 5, the first 3 bands are brown, black and blue and the fourth band the multiplier is green. Then again, there's always the calculator which makes things much easier to solve. The forms of practical capacitors vary widely, but all contain at least two electrical conductors plates separated by a dielectric i.
The conductors can be thin films of metal, aluminum foil or disks, etc. The 'non-conducting' dielectric acts to increase the capacitor's charge capacity. A dielectric can be glass, ceramic, plastic film, air, paper, mica, etc. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.
If a battery has been attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. An ideal capacitor is characterized by a single constant value for its capacitance. Capacitance is expressed as the ratio of the electric charge Q on each conductor to the potential difference V between them. The capacitance is greater when there is a narrower separation between conductors and when the conductors have a larger surface area.
In practice, the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce an under sired inductance and resistance. So it can be said to act somewhat like a switch. A specific arrangement of diodes can convert AC to pulsating DC, hence it is sometimes also called as a rectifier. It is derived from "di-ode " which means a device having two electrodes.
The symbol of a p-n junction diode is shown below, the arrowhead points in the direction of conventional current flow. The p-n junction is a basic building block in any semiconductor device.
Hence it is a device with two elements, the p-type forms anode and the n-type forms the cathode. These terminals are brought out to make the external connections. The n side will have large number of electrons and very few holes due to thermal excitation whereas the p side will have high concentration of holes and very few electrons.
Due to this a process called diffusion takes place. In this process free electrons from the n side will diffuse spread into the p side and combine with holes present there, leaving a positive immobile not moveable ion in the n side. Hence few atoms on the p side are converted into negative ions. Similarly few atoms on the n-side will get converted to positive ions. Due to this large number of positive ions and negative ions will accumulate on the n-side and p-side respectively.
This region so formed is called as depletion region. Due to the presence of these positive and negative ions a static electric field called as "barrier potential" is created across the p-n junction of the diode.
It is called as "barrier potential" because it acts as a barrier and opposes the flow of positive and negative ions across the junction. These are example of electro- luminescence, the process in which emission of photos takes place by the recombination of excess electrons and holes in a direct band gap semiconductor.
The LED images given below. When the level is at L1 the liquid will be height h1 above switch. The resulting switch closure can energize the solenoid valve V1 causing an inflow to the tank. Assuming the valve is correctly sized, this will cause a rise in the level back towards the setpoint. In order to arrest the rise in level the built in differential feature of the switch can be employed to de-energize the solenoid valve when level L2 is reached.
This system will achieve a mean level in the tank about the desired setpoint. Clearly it is impossible to maintain the system at the setpoint since there must be a difference in the operating levels L1 and L2 as the valve can only be energized or de-energized. It is often counter productive to try to reduce the differential between L1 and L2 to too small a value as this will result in excessive cycling, and hence wear, of the valve.
Usual practice is to control with a deadband about the setpoint as shown in Below Figure. Typical uses in electric heater controls. Following are a few aspects of On-Off Control that you should keep in mind when considering it for commercial application:. Unlike intermediate value or PID control, there is no in between. On-Off Control can result in excessive variability as the controller has so few options for maintaining Set Point.
A process equipped with On-Off Control will constantly overshoot its Set Point and cycle as a result. The work demanded of the FCE regularly accelerates the time to failure and increases maintenance costs. Don't Miss Our Updates. Be the first to get exclusive content straight to your email.
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