This be high current power supply circuit , Which there is the size voltage 13.8V at 20A.By it uses base equipment that seeks to buy easy, be integrated number circuit LM741 perform maintain one’s position voltage be stable or Regulated at 13.8V. Which can fine can decorate a little again. Besides still have the power transistors 2N3055 X4 numbers bring to build parallel perform enlarge current tall arrive at 20Amp Other detail , see in the circuit.
A very simple alarm project electronic circuit can be designed using a common 741 operational amplifier IC and some other common electronic parts . As you can see in the schematic circuit , this alarm project is activated by some normal open contacts , connected in parallel . If one of those contact is closed the alarm will sound .
This alarm project is composed from an audio frequency generator , a small audio amplifier stage and a small command stage .
The audio frequency generator is designed using a 741 operational amplifier ( or some other similar type ) .The T2 and T2 transistors forms a small audio amplifier and the normal opened contacts I1to I3 forms the command stage ( you can use how many contacts you need ).
In stand-by mode when all contacts are opened T1 transistor is locked and the alarm is inactive . If one of the contact is closed T1 transistor will activate the relay that will activate alarm . One the alarm starts to sound it can not be stopped until the I contact will be opened ( the circuit will be unplugged from the power source) .
The relay used in this project must have a 12 volts nominal voltage ( 10 volts activation) with a maximum working current of 10-30mA.
This circuit project must be powered from a 12 volt DC power supply .
This very simple toy uses a magnetic chain reaction to launch a steel marble at a target at high speed. The toy is very simple to build, going together in minutes, and is very simple to understand and explain, and yet fascinating to watch and to use.
The photo above shows six frames of video showing the gauss rifle in action. Each frame shows 1/30th of a second. In the first frame, a steel ball starts rolling towards a magnet taped to a wooden ruler. In the second frame, a second ball can be seen speeding between the rightmost two magnets. By the third frame, the accelerator has sped up so much that the ball that is seen leaving the left side of the device is just a blur as it smashes into the target. One ball, starting at rest, has caused another ball to leave the device at a very high speed.
S:sci-toys.com
The candle flame will heat up the magnetic material until it loses its ability to be magnetized. Gravity will then pull it away from the magnet (and thus away from the flame). The magnetic material will cool down a little bit once it is away from the flame, and regain its ability to stick to the magnet. The magnet will then pull it up into the flame, and the whole process repeats.
All the parts can be found at Radio Shack, but if you want to build the engine using a Canadian nickel, any hardware store will have the other parts you need.
You will need some copper or brass wire, a large ceramic magnet (the cheap kind that Radio Shack sells for about a dollar), and a candle.
We want the pendulum to swing back and forth only, so we use two wires to hold it up. Cut about a foot of wire and wrap the center of the wire around the large magnet. Then form the two ends into small loops and bend them up to form the support for the pendulum.
If you are using the rare-earth magnet for the pendulum's weight, it helps at this point to demagnetize it by holding it in a candle flame. You can stick it onto a coat hanger and hold the magnet in the flame until it falls off. This will prevent the magnet from jumping onto the large ceramic magnet while we adjust the pendulum.
Wrap another foot of wire around the nickel or the rare-earth magnet that will form the weight for the pendulum. Form the two ends of the wire into loops that slip into the loops of the pendulum support. Make sure that the pendulum weight is just close enough to the magnet that it rises to it when the pendulum is vertical. The wires of the pendulum and its support should be long enough that the weight can fall away from the flame and hang vertically when it is demagnetized.
With the pendulum stuck to the large magnet, position a short (lighted) candle so that the flame just touches the weight. You may need to shield the flame from drafts so it remains steady. The flame will heat the rare-earth alloy until it loses its ability to stick to the large ceramic magnet. It will then fall away, and swing a few times as it cools. When it is cool enough to be magnetized again, it will rise and stick to the magnet, where the flame will again heat it up.
If the weight still touches the flame when it has fallen away from the magnet, adjust the pendulum's supports a little so that the weight rests a little farther away. If the weight is so far away that the magnet cannot pull it back up once it is magnetized, adjust the supports to bring it closer. Be careful when adjusting the supports, since they may be quite hot. Also be careful to move the candle so as not to burn yourself on the candle flame. When the engine is adjusted just right, it will settle down to a predictable swing, often taking only one swing to cool enough to stick to the magnet again. It will run as long as the candle burns.
If you have chosen to use the Canadian nickel, you will need a heat source better than the candle. A small alcohol lamp or fondue pot burner will do nicely. You may have to make the pendulum support wires longer to make room for the lamp.
S:sci-toys.com
We have all played with magnets. A pair of magnets by itself makes a wonderful toy. Today's magnets are even better than the best ones I remember playing with as a child. At toy stores and Radio Shack you can get flexible magnetic strips of plastic that can be cut into shapes with scissors. You can also get cheap and brittle ceramic magnets, stronger Alnico magnets, and even the new super strong rare-earth magnets. These are made of neodymium-iron-boron or samarium-cobalt, and are very powerful. At the end of this section I will list some sources I have found for good or cheap (or good and cheap) magnets. Some particularly nice tiny ones can be found in our catalog.
Through mail-order surplus houses you can get large neodymium-iron-boron magnets of incredible strength. For about five dollars each you can get magnets that will hold paperback books onto your refrigerator, or drag each other around a two-inch thick table, one on top of the table and one hidden underneath. I once entertained my guests and several waiters at a restaurant by mysteriously moving the stainless flatware around the table. People are not used to the effects of powerful magnets. They are amazed even when they can see what you are doing.
Because of their high strength-to-weight ratios, neodymium-iron-boron magnets seem to be little affected by gravity. Small ones can be placed on either side of a nose and will stay there until the wearer laughs so hard they slide upwards against gravity and snap together. Temporary earrings are also popular. Handle larger magnets with care, since they will pinch hard enough to cause blisters if they are separated only by small bits of skin. They are also easily capable of erasing the magnetically stored information on credit cards, computer floppy disks, and cassette tapes, so take care when selecting a pocket for them.
If you are showing magnets to a very young person for the first time, there are several tricks you will not want to forget. Use some large cheap ceramic magnets from Radio Shack or a toy store so they will not be easily lost or swallowed. Show how they attract and repel each other. At Radio Shack you can get some donut-shaped magnets that can slide over a pencil. The child can stack several so they each repel, forming a magic spring.
The oscillator is built into a metal can. The corners of the can are rounded, except for the lower left corner, which is sharp. This indicates the where the unused lead is. The lead is there to help hold the can down firmly on the printed circuit board, but it is not connected to anything inside the can.
The other main part is the audio transformer . In this circuit it is used as a modulator. The modulator changes the strength of the radio waves to match the loudness of the music or voice we want to transmit.
A pictorial diagram of the transmitter looks like this:
A photograph of the completed transmitter is shown below:
The transformer has two leads on one side, (red and white in the photo ) and three leads on the other side (blue, black and green in the photo). The two leads are the low impedance side of the transformer, (the 8 ohm side). The three leads are the high impedance side (the 1000 ohm side). The middle of the three leads is called the center tap, and we won't be using it in this circuit.
To get the best range, we put the low impedance side of the transformer in series with the oscillator. This means that the signal source must be capable of driving heavy loads, like an 8 ohm speaker.
If you are trying to use a weaker signal source, such as an iPod or some other MP3 player that can only drive 32 ohm earphones, you will want to reverse the transformer, so that the 1,000 ohm side is in series with the oscillator, and the 8 ohm side is connected to your signal source. You will get slightle less range, but your odds of getting some modulation of the signal will be much better.
S:sci-toys.com
S:www.instructables.com The transmitter goes together in about 10 minutes, and is small enough to fit in the palm of your hand.
Depending on the antenna, the transmitter can send voice and music across the room, or across the street.
I put together my first version with simple clip leads (no soldering, no printed circuit board, not even a battery clip). This version is much sturdier and convenient.
S:sci-toys.com
A bipolar base region can be fabricated that is much smaller than any CMOS transistor gate. This smaller size enables bipolar transistors to operate much faster than CMOS transistors. Bipolar transistors are typically used in applications where speed is very important, such as in radio-frequency ICs. On the other hand, although bipolar transistors are faster, FETs use less current. The type of switch a designer selects depends on which benefits are more important for the application: speed or power savings. This is one of many trade-off decisions engineers make in designing their circuits.
Most ICs are made of silicon, which is abundant in ordinary beach sand. Pure crystalline silicon, as with other semiconducting materials, has a very high resistance to electrical current at normal room temperature. However, with the addition of certain impurities, known as dopants, the silicon can be made to conduct usable currents. In particular, the doped silicon can be used as a switch, turning current off and on as desired.
The process of introducing impurities is known as doping or implantation. Depending on a dopant’s atomic structure, the result of implantation will be either an n-type (negative) or a p-type (positive) semiconductor. An n-type semiconductor results from implanting dopant atoms that have more electrons in their outer (bonding) shell than silicon, as shown in the figure. The resulting semiconductor crystal contains excess, or free, electrons that are available for conducting current. A p-type semiconductor results from implanting dopant atoms that have fewer electrons in their outer shell than silicon. The resulting crystal contains “holes” in its bonding structure where electrons would normally be located. In essence, such holes can move through the crystal conducting positive charges.
S:britannica.com
All ICs use the same basic principles of voltage (V), current (I), and resistance (R). In particular, equations based on Ohm’s law, V = IR, determine many circuit design choices. Design engineers must also be familiar with the properties of various electronic components needed for different applications.
As mentioned earlier, an analog circuit takes an infinitely variable real-world voltage or current and modifies it in some useful way. The signal might be amplified, compared with another signal, mixed with other signals, separated from other signals, examined for value, or otherwise manipulated. For the design of this type of circuit, the choice of every individual component, size, placement, and connection is crucial. Unique decisions abound—for instance, whether one connection should be slightly wider than another connection, whether one resistor should be oriented parallel or perpendicular to another, or whether one wire can lie over the top of another. Every small detail affects the final performance of the end product.
When integrated circuits were much simpler, component values could be calculated by hand. For instance, a specific amplification value (gain) of an amplifier could typically be calculated from the ratio of two specific resistors. The current in the circuit could then be determined, using the resistor value required for the amplifier gain and the supply voltage used. As designs became more complex, laboratory measurements were used to characterize the devices. Engineers drew graphs of device characteristics across several variables and then referred to those graphs as they needed information for their calculations. As scientists improved their characterization of the intricate physics of each device, they developed complex equations that took into account subtle effects that were not apparent from coarse laboratory measurements. For example, a transistor works very differently at different frequencies, sizes, orientations, and placements. In particular, scientists found parasitic components (unwanted effects, usually resistance and capacitance) that are inherent in the way the devices are built. Parasitics become more problematic as the circuitry becomes more sophisticated and smaller and as it runs at higher frequencies.
Although parasitic components in a circuit can now be accounted for by sophisticated equations, such calculations are very time-consuming to do by hand. For this work computers have become indispensable. In particular, a public-domain circuit-analysis program developed at the University of California, Berkeley, during the 1970s, SPICE (Simulation Program with Integrated Circuit Emphasis), and various proprietary models designed for use with it are ubiquitous in engineering courses and in industry for analog circuit design. SPICE has equations for transistors, capacitors, resistors, and other components, as well as for lengths of wires and for turns in wires, and it can reduce the calculation of circuit interactions to hours from the months formerly required for hand calculations.
Since digital circuits involve millions of times as many components as analog circuits, much of the design work is done by copying and reusing the same circuit functions, especially by using digital design software that contains libraries of prestructured circuit components. The components available in such a library are of similar height, contain contact points in predefined locations, and have other rigid conformities so that they fit together regardless of how the computer configures a layout. While SPICE is perfectly adequate for analyzing analog circuits, with equations that describe individual components, the complexity of digital circuits requires a less-detailed approach. Therefore, digital analysis software ignores individual components for mathematical models of entire preconfigured circuit blocks (or logic functions).
Whether analog or digital circuitry is used depends on the function of a circuit. The design and layout of analog circuits are more demanding of teamwork, time, innovation, and experience, particularly as circuit frequencies get higher, though skilled digital designers and layout engineers can be of great benefit in overseeing an automated process as well. Digital design emphasizes different skills from analog design.
A p-n junction that conducts electricity when energy is added to the n material is called forward-biased because the electrons move forward into the holes. If voltage is applied in the opposite direction—a positive voltage connected to the n side of the junction—no current will flow. The electrons in the n material will still be attracted to the positive voltage, but the voltage will now be on the same side of the barrier as the electrons. In this state a junction is said to be reverse-biased. Since p-n junctions conduct electricity in only one direction, they are a type of diode. Diodes are essential building blocks of semiconductor switches.
S:.britannica.com
Just like a marching band, the circuits perform their logic function only on direction by the bandmaster. The bandmaster in a microprocessor, so to speak, is called the clock. The clock is a signal that quickly alternates between two logic states. Every time the clock changes state, every logic circuit in the microprocessor does something. Calculations can be made very quickly, depending on the speed (“clock frequency”) of the microprocessor.
Microprocessors contain some circuits, known as registers, that store information. Registers are predetermined memory locations. Each processor has many different types of registers.Permanent registers are used to store the preprogrammed instructions required for various operations (such as addition and multiplication). Temporary registers store numbers that are to be operated on and also the result. Other examples of registers include the “program counter,” the “stack pointer,” and the “address” register.
Microprocessors can perform millions of operations per second on data. In addition to computers, microprocessors are common in video game systems, televisions, cameras, and automobiles.
Integrated circuits have their origin in the invention of the transistor in 1947 by William B. Shockley and his team at the American Telephone and Telegraph Company’s Bell Laboratories. Shockley’s team (including John Bardeen and Walter H. Brattain) found that, under the right circumstances, electrons would form a barrier at the surface of certain crystals, and they learned to control the flow of electricity through the crystal by manipulating this barrier. Controlling electron flow through a crystal allowed the team to create a device that could perform certain electrical operations, such as signal amplification, that were previously done by vacuum tubes. They named this device a transistor, from a combination of the words transfer and resistor (see photograph). The study of methods of creating electronic devices using solid materials became known as solid-state electronics. Solid-state devices proved to be much sturdier, easier to work with, more reliable, much smaller, and less expensive than vacuum tubes. Using the same principles and materials, engineers soon learned to create other electrical components, such as resistors and capacitors. Now that electrical devices could be made so small, the largest part of a circuit was the awkward wiring between the devices.
In 1958 Jack Kilby of Texas Instruments, Inc., and Robert Noyce of Fairchild Semiconductor Corporation independently thought of a way to reduce circuit size further. They laid very thin paths of metal (usually aluminum or copper) directly on the same piece of material as their devices. These small paths acted as wires. With this technique an entire circuit could be “integrated” on a single piece of solid material and an integrated circuit (IC) thus created. ICs can contain hundreds of thousands of individual transistors on a single piece of material the size of a pea. Working with that many vacuum tubes would have been unrealistically awkward and expensive. The invention of the integrated circuit made technologies of the Information Age feasible. ICs are now used extensively in all walks of life, from cars to toasters to amusement park rides.
![Different combinations of logic circuits. [Credit: Encyclopædia Britannica, Inc.]](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uPJigEXV6430OJJxBOohLKmOcteEXZB9g_6k2sCQm7VOZLwtYVCIoq6KnY5yF9GGuAAQWv2656Vj35D_R_76Cg7zZiZDyTAMP9c6D4jgX8aZCHPwVOcKtRskz2Yn9fmvrURKAw1PI34g=s0-d "Different combinations of logic circuits. [Credit: Encyclopædia Britannica, Inc.]")
A digital circuit, on the other hand, is designed to accept only voltages of specific given values. A circuit that uses only two states is known as a binary circuit. Circuit design with binary quantities, “on” and “off” representing 1 and 0 (i.e., true and false), uses the logic of Boolean algebra. The three basic logic functions—NOT, AND, and OR—together with their truth tables are given in the figure. (Arithmetic is also performed in the binary number system employing Boolean algebra.) These basic elements are combined in the design of ICs for digital computers and associated devices to perform the desired functions.
S:britannica.com
SWITCH
(1) In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.
(2) A small lever or button. The switches on the back of printers and on expansion boards are called DIP switches. A switch that has just two positions is called a toggle switch.
(3) Another word for option or parameter -- a symbol that you add to a command to modify the command's behavior.
S:webopedia.com
The old telephone system (PSTN) uses circuit switching to transmit voice data whereas VoIP uses packet-switching to do so. The difference in the way these two types of switching work is the thing that made VoIP so different and successful.
To understand switching, you need to realize that the network in place between two communicating persons is a complex field of devices and machines, especially if the network is the Internet. Consider a person in Mauritius having a phone conversation with another person on the other side of the globe, say in the US. There are a large number of routers, switches and other kinds of devices that take the data transmitted during the communication from one end to the other.
In circuit-switching, this path is decided upon before the data transmission starts. The system decides on which route to follow, based on a resource-optimizing algorithm, and transmission goes according to the path. For the whole length of the communication session between the two communicating bodies, the route is dedicated and exclusive, and released only when the session terminates.
Once they reach their destination, the packets are reassembled to make up the original data again. It is therefore obvious that, to transmit data in packets, it has to be digital data.
In packet-switching, the packets are sent towards the destination irrespective of each other. Each packet has to find its own route to the destination. There is no predetermined path; the decision as to which node to hop to in the next step is taken only when a node is reached. Each packet finds its way using the information it carries, such as the source and destination IP addresses.
As you must have figured it out already, traditional PSTN phone system uses circuit switching while VoIP uses packet switching.
DIP switches enable you to configure a circuit board for a particular type of computer or application. The installation instructions should tell you how to set the switches. DIP switches are always toggle switches, which means they have two possible positions -- on or off. (Instead of on and off, you may see the numbers 1 and 0.)
One of the historic advantages of the Macintosh over the PC was that it allowed you to configure circuit boards by entering software commands instead of setting DIP switches. However, the new Plug & Play standard developed by Microsoft makes DIP switches obsolete for PC expansion cards too.
S:webopedia.com
A type of communications in which a dedicated channel (or circuit) is established for the duration of a transmission. The most ubiquitous circuit-switching network is the telephone system, which links together wire segments to create a single unbroken line for each telephone call.
The other common communications method is packet switching, which divides messages into packets and sends each packet individually. The Internet is based on a packet-switching protocol, TCP/IP.
Circuit-switching systems are ideal for communications that require data to be transmitted in real-time. Packet-switching networks are more efficient if some amount of delay is acceptable.
Circuit-switching networks are sometimes called connection-oriented networks. Note, however, that although packet switching is essentially connectionless, a packet switching network can be made connection-oriented by using a higher-level protocol. TCP, for example, makes IP networks connection-oriented.
S:webopedia.com
Digital electronics is classified into combinational logic and sequential logic. Combinational logic output depends on the inputs levels, whereas sequential logic output depends on stored levels and also the input levels.
| |||||||||||||||||
|
