PN Junction - working principle

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Inside a CPU

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Elektrisches Feld (Electric Field)

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Elektrische Ladung (Electric Charge)

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TIWL - Electricity and Magnetism 02 - Electric Field Lines, Superposition, Inductive Charging, Induced Dipoles

 

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TIWL - Electricity and Magnetism 01 - Electric Charges and Forces - Coulomb's Law - Polarization

 

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Resistance

 

An electron traveling through the wires and loads of the external circuit encounters resistance. Resistance is the hindrance to the flow of charge. For an electron, the journey from terminal to terminal is not a direct route. Rather, it is a zigzag path that results from countless collisions with fixed atoms within the conducting material. The electrons encounter resistance - a hindrance to their movement. While the electric potential difference established between the two terminals encourages the movement of charge, it is resistance that discourages it. The rate at which charge flows from terminal to terminal is the result of the combined effect of these two quantities.

The flow of charge through wires is often compared to the flow of water through pipes. The resistance to the flow of charge in an electric circuit is analogous to the frictional effects between water and the pipe surfaces as well as the resistance offered by obstacles that are present in its path. It is this resistance that hinders the water flow and reduces both its flow rate and its drift speed. Like the resistance to water flow, the total amount of resistance to charge flow within a wire of an electric circuit is affected by some clearly identifiable variables.

First, the total length of the wires will affect the amount of resistance. The longer the wire, the more resistance that there will be. There is a direct relationship between the amount of resistance encountered by charge and the length of wire it must traverse. After all, if resistance occurs as the result of collisions between charge carriers and the atoms of the wire, then there is likely to be more collisions in a longer wire. More collisions mean more resistance.

 

Second, the cross-sectional area of the wires will affect the amount of resistance. Wider wires have a greater cross-sectional area. Water will flow through a wider pipe at

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Resistors

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage levels within circuits.

A number of different resistors are shown in the photos. (The resistors are on millimeter paper, with 1cm spacing to give some idea of the dimensions).  Photo below shows some low-power resistors, with power dissipation below 5 watt (most commonly used types) are cylindrical in shape, with a wire protruding from each end for connecting to a circuit.

 

This photo shows some higher-power resistors, with power dissipation above 5 watt are shown below.

 

 

 

 

The symbol for a resistor is shown in the following diagram (upper: American symbol, lower: European symbol.)

 

Resistor symbols

 

 The unit for measuring resistance is the OHM. (the Greek letter Ω - called Omega). Higher resistance values are represented by "k" (kilo-ohms) and M (meg ohms). For example, 120 000 Ω is represented as 120k, while 1 200 000 Ω is represented as 1M2. The dot is generally omitted as it can easily be lost in the printing process. In some circuit diagrams, a value such as 8 or 120 represents a resistance in ohms. Another common practice is to use the letter E for resistance in ohms. The letter R can also be used. For example, 120E (120R) stands for 120

 

Resistor Markings

Resistance value is marked on the resistor body. Most resistors have 4 bands. The first two bands provide the numbers for the resistance and the third band provides the number of zeros. The fourth band indicates the tolerance. Tolerance values of  5%, 2%, and 1% are most commonly available.

The following table shows the colors used to identify resistor values:

 

 

a. Four-band resistor, b. Five-band resistor, c. Cylindrical SMD resistor, d. Flat SMD resistor

 

RESISTORS LESS THAN 10 OHMS

When the third band is gold, it indicates the value of the "colors" must be divided by 10.
Gold = "divide by 10" to get values 1R0 to 8R2
See 1st Column above for examples.

When the third band is silver, it indicates the value of the "colors" must be divided by 100.
(Remember: more letters in the word "silver" thus the divisor is "larger.")
Silver = "divide by 100" to get values 0R1 (one tenth of an ohm) to 0R82
e.g: 0R1 = 0.1 ohm     0R22 =  point 22 ohms  
See 4th Column above for examples.

The letters "R, k and M" take the place of a decimal point. The letter "E" is also used to indicate the word "ohm."
e.g: 1R0 = 1 ohm     2R2 = 2 point 2 ohms   22R = 22 ohms  
2k2 = 2,200 ohms     100k = 100,000 ohms
2M2 = 2,200,000 ohms

Common resistors have 4 bands. These are shown above. First two bands indicate the first two digits of the resistance, third band is the multiplier (number of zeros that are to be added to the number derived from first two bands) and fourth represents the tolerance.
Marking the resistance with five bands is used for resistors with tolerance of 2%, 1% and other high-accuracy resistors. First three bands determine the first three digits, fourth is the multiplier and fifth represents the tolerance.

For SMD (Surface Mounted Device) the available space on the resistor is very small. 5% resistors use a 3 digit code, while 1% resistors use a 4 digit code.
Some SMD resistors are made in the shape of small cylinder while the most common type is flat. Cylindrical SMD resistors are marked with six bands - the first five are "read" as with common five-band resistors, while the sixth band determines the Temperature Coefficient (TC), which gives us a value of resistance change upon 1-degree temperature change.
The resistance of flat SMD resistors is marked with digits printed on their upper side. First two digits are the resistance value, while the third digit represents the number of zeros. For example, the printed number 683 stands for 68000W , that is 68k.
It is self-obvious that there is mass production of all types of resistors. Most commonly used are the resistors of the E12 series, and have a tolerance value of 5%. Common values for the first two digits are: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68 and 82.
The E24 series includes all the values above, as well as: 11, 13, 16, 20, 24, 30, 36, 43, 51, 62, 75 and 91. What do these numbers mean?  It means that resistors with values for digits "39" are: 0.39W, 3.9W, 39W, 390W, 3.9kW, 39kW, etc are manufactured. (0R39, 3R9, 39R, 390R, 3k9, 39k)
For some electrical circuits, the resistor tolerance is not important and it is not specified. In that case, resistors with 5% tolerance can be used. However, devices which require resistors to have a certain amount of accuracy, need a specified tolerance.

 

Resistor Power Dissipation

If the flow of current through a resistor increases,  it heats up, and if the temperature exceeds a certain critical value, it can be damaged. The wattage rating of a resistor is the power it can dissipate over a long period of time.
Wattage rating is not identified on small resistors. The following diagrams show the size and wattage rating:

Resistor dimensions

 

Most commonly used resistors in electronic circuits have a wattage rating of 1/2W or 1/4W. There are smaller resistors  (1/8W and 1/16W) and higher (1W, 2W, 5W, etc).
In place of a single resistor with specified dissipation, another one with the same resistance and higher rating may be used, but its larger dimensions increase the space taken on a printed circuit board as well as the added cost.
Power (in watts) can be calculated according to one of the following formulae, where U is the symbol for Voltage across the resistor (and is in Volts), I is the symbol for Current in Amps and R is the resistance in ohms:

 

For example, if the voltage across an 820 Ω resistor is 12V, the wattage dissipated by the resistors is:

 

A 1/4W resistor can be used.

In many cases, it is not easy to determine the current or voltage across a resistor. In this case the wattage dissipated by the resistor is determined for the "worst" case. We should assume the highest possible voltage across a resistor, i.e. the full voltage of the power supply (battery, etc).
If we mark this voltage as U_B, the highest dissipation is:

For example, if U_B=9V, the dissipation of a 220 Ω resistor is:

 

A 0.5W or higher wattage resistor should be used.

 

 

 

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Ohm's Law

 

The relationship between Voltage, Current and Resistance in any DC electrical circuit was firstly discovered by the German physicist Georg Ohm. Ohm found that, at a constant temperature, the electrical current flowing through a fixed linear resistance is directly proportional to the voltage applied across it, and also inversely proportional to the resistance.

This relationship between the Voltage, Current and Resistance forms the bases of Ohms Law and is shown below.

 

 Ohm's Law Relationship

 

By knowing any two values of the Voltage, Current or Resistance quantities we can use Ohm's Law to find the third missing value. Ohm's Law is used extensively in electronics formulas and calculations so it is “very important to understand and accurately remember these formulas”.

 

To find the Voltage ( V )

[ V = I x R ]      V (volts) = I (amps) x R (Ω)

 

To find the Current ( I )

[ I = V ÷ R ]      I (amps) = V (volts) ÷ R (Ω)

 

To find the Resistance ( R )

[ R = V ÷ I ]      R (Ω) = V (volts) ÷ I (amps)

 

It is sometimes easier to remember Ohms law relationship by using pictures. Here the three quantities of V, I and R have been superimposed into a triangle (affectionately called the Ohm's Law Triangle) giving voltage at the top with current and resistance at the bottom. This arrangement represents the actual position of each quantity in the Ohms law formulas.

 

Ohms Law Triangle

 

Transposing the above Ohms Law equation gives us the following combinations of the same equation:

 

Then by using Ohms Law we can see that a voltage of 1V applied to a resistor of 1Ω will cause a current of 1A to flow and the greater the resistance, the less current will flow for any applied voltage. Any Electrical device or component that obeys “Ohms Law” that is, the current flowing through it is proportional to the voltage across it ( I α V ), such as resistors or cables, are said to be “Ohmic” in nature, and devices that do not, such as transistors or diodes, are said to be “Non-ohmic” devices.

 

Ohm's Law Example

For the circuit shown below find the Voltage (V), the Current (I), the Resistance (R)

 

Voltage   [ V = I x R ] = 2 x 12Ω = 24V

Current   [ I = V ÷ R ] = 24 ÷ 12Ω = 2A

Resistance   [ R = V ÷ I ] = 24 ÷ 2 = 12 Ω

Georg Simon Ohm, Alessandro Volta, André-Marie Ampère

 

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Programmable Logic Controller

Every aspect of industry - from power generation to automobile painting to food packaging - uses programmable controllers to expand and enhance production. In this book, you will learn about all aspects of these powerful and versatile tools. This article will introduce you to the basics of programmable controllers - from their operation to their vast range of applications. In it, we will give you an inside look at the design philosophy behind their creation, along with a brief history of their evolution. We will also compare programmablecontrollers to other types of controls to highlight the benefits anddrawbacks of each, as well as pinpoint situations where PLCs work best. When you finish this chapter, you will understand the fundamentals of programmable controllers and be ready to explore the number systemsassociated with them.

Programmable logic controllers, also called programmable controllers or PLCs, are solid-state members of the computer family, using integrated circuits instead of electromechanical devices to implement control functions. They are capable of storing instructions, such as sequencing, timing, counting, arithmetic, data manipulation, and communication, to control industrial machines and processes. Figure below illustrates a conceptual diagram of a PLC application.

PLC conceptual application diagram

Programmable controllers have many definitions. However, PLCs can be thought of in simple terms as industrial computers with specially designed architecture in both their central units (the PLC itself) and their interfacing circuitry to field devices (input/output connections to the real world).

Control engineering has evolved over time. In the past humans were the main method for controlling a system. More recently electricity has been used for control and early electrical control was based on relays. These relays allow power to be switched on and off without a mechanical switch. It is common to use relays to make simple logical control decisions. The development of low cost computer has brought the most recent revolution, the Programmable Logic Controller (PLC). The advent of the PLC began in the 1970s, and has become the most common choice for manufacturing controls.

PLCs have been gaining popularity on the factory floor and will probably remain predominant for some time to come. Most of this is because of the advantages they offer.

• Cost effective for controlling complex systems.
• Flexible and can be reapplied to control other systems quickly and easily.
• Computational abilities allow more sophisticated control.
• Trouble shooting aids make programming easier and reduce downtime.
• Reliable components make these likely to operate for years before failure.

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Introduction to ATMEGA 32

To give you a basic understanding of the microcontroller, the AVR Atmega32 microcontroller is considered to be a computer on a chip. The microcontroller is able to execute a set of instructions in the form of a program. The program language that I will be using for theseprojects is C++. To giv ethe usersof this website the best opportunity to learn, the C++ programs will be explained is great detail.

The really cool thing about microcontrollers is that you have control over all the pins. For a beginner, this can be a difficult concept to understand, especially having no experience with electronics. Don't fret, I will walk you through each tiny detail. Each pin has a special assignment, or can be used as an input or output feature, with a few exceptions, the power pins.

On the left hand side of the chip, looking at it form the top and the little triangle is at the top left, there are 20 pins (this is a 40 pin microcontroller). The first starting from the top left are the PB0-7 pins. That's a total of 8 pins as the index of these pins and most everything in the program starts with an index at 0. This set of pins are called "Port B" and there are 3 other ports labeled from A to D. These ports can be set to receive information and is called INPUT and they can be set to send voltage out in some form called OUTPUT. General power pins to receive the power for the chip called VCC and GND. All but one pin of Port D (PD0-6) is also located on the left side (lower section). PD7 (Pin 7 of Port D) is all alone starting the right hand side of the microcontroller.

Continuing on the right side, and the ending of Port D, Port C continued from the lower corner up. From there on, may favorite pins continue, the analog to digital pins. These pins have the capability to sense the environment with the help of components that feed these pins an analog voltage. Dopn't worry about not understanding analog or even digita at this point, it will be explained in greter detail later. These analog to digidal converter pins compose Port A.

One example of the use of the analong to digital conversion would be, say, sensing the temperature. You can connect a component that converts temperature to a level of voltage called a thermistor to one of the Port A pins and the microcontroller will convert this voltage to a number from 0 to 255 (an 8-bit number - higher resolution is possible at 10-bits). The program that is written and stored into the microcontroller can use this temperature and respond in a specific way. For example, if you have the thermistor against a boiling pot, the microcontroller can respond and provide an output to another pin that beeps, or flashes a light.

Other features of this and other microcontrollers, other than the actual programming is the programming space (where the program is stored in the chip and how much space you have), memory, or space for data and variables that the program will use, and finally, there is a clock built into the chip that counts. The counting can be in many different speeds depending on the speed of the chip and the divisor that is selected for the speed. This is starting to get complicated, so I will back up. The counting can be in seconds, miliseconds, microseconds, or whatever you determine for the program and application that you select.

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Evolution of microcontrollers

The first microprocessor, named the 4004, was introduced by the Intel Corporation in 1971. This was a simple 4-bit device, supported by three other chips to make a computer; the 4001 and 4002 memory chips, and the 4003 shift register. 4004 was initially used in calculators and in simple control applications.
Shortly after the 4004 appeared in the commercial marketplace, many electronic companies realised the power and future prospects of microprocessors and so have heavily invested in this field. Three other general-purpose microprocessors were soon introduced: Rockwell International 4-bit PPS-4, Intel 8-bit 8008 and the National Semiconductor 16-bit IMP-16. These microprocessors were based on PMOS technology and can be classified as the firstgeneration devices.
In the early 1970s, we see the second-generation microprocessors in the marketplace, designed using the NMOS technology. The shift to NMOS technology resulted in higher execution speeds, as well as higher chip densities. During this time, we see 8-bit microprocessors such as the Motorola 6800, Intel 8080 and 8085, the highly popular Zilog Z80, and Motorola 6800 and 6809.

The third generation of microprocessors were based on HMOS technology, which resulted in higher speeds and, more importantly, higher chip densities. During 1978, we see the 16-bitmicroprocessors such as the Intel 8086, Motorola 68 000 and Zilog Z8000. The 8086 microprocessorwas so successful that it was used in early PC designs (called PC XT).

The fourth generation of microprocessors appeared around the 1980s and the technology was based on HCMOS. During this generation we see the introduction of 32-bit devices into the marketplace. Intel introduced the highly popular 32-bit microprocessors 80 386, 80 486, and the Pentium family; and Motorola introduced the 68 020 family. The Intel processors have been used heavily in early PC designs. In parallel to the development of 32-bit microprocessors, we see the introduction of early single chip computers (later named microcontrollers) into the marketplace.

The Intel 8048 was the first microcontroller, followed by the highly popular 8051 series. The 8051 device has been so popular that it is still in use today. This device was a true single chip computer, containing a CPU, data memory and erasable program memories, I/O module, timer/counter, interrupt logic, clock logic, and serial communications module, such as the Universal Synchronous Asynchronous Receiver Transmitter (USART). After the success of the 8051, we see many other companies offering microcontrollers. Today, some of the most popular general-purpose low-cost 8-bit microcontrollers are Microchip PIC series, Atmel AVR series, Motorola HC11 series, and 8051 and its derivatives.

The fifth and the current generation of microcontrollers are now based on 16-bit and 32-bitarchitectures (e.g. PIC32 series). It is interesting to note that currently the 8-bit microcontrollers are still popular and much more in demand. This is because of their simple architectures, low cost, low power requirements, and the availability of the vast number of hardware and software development tools. The power offered by the high-end 8-bit microcontrollers (e.g. the PIC18F series) are enough for most medium to high-speed applications, except perhaps in special cases of digital signal processing where much higher throughput is generally required.

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Microcontroller

A microcontroller (sometimes abbreviated µC, uC or MCU) is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications.

Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, toys and other embedded systems. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems.

Some microcontrollers may use four-bit words and operate at clock rate frequencies as low as 4 kHz, for low power consumption (single-digit milliwatts or microwatts). They will generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just nanowatts, making many of them well suited for long lasting battery applications. Other microcontrollers may serve performance-critical roles, where they may need to act more like a digital signal processor (DSP), with higher clock speeds and power consumption.

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Single board computer

A single board computer (SBC) is a type of computer with all of its components built onto a single circuit board. The size of an SBC can vary from about the size of a credit card to that of a video game console. They are often incorporated into larger devices such as automatic teller machines, industrial and medical equipment, or robotic devices. Since the mid 2000s, inexpensive single board computers have been used by educators and hobbyists.

Desktop and even laptop personal computers (PCs) generally have separate components connected to a central circuit board through cables or buses. A single board computer packs all of its necessary components, including the microprocessor, memory, and storage, onto a single circuit board. Many SBCs are built to be PC-compatible and use the same processors, memory, and graphics chips as standard PCs. Other units include different types of hardware and some feature a microcontroller, a specialized processor with built-in input/output functions. Some SBCs are expandable or partially reconfigurable, while others are stuck with what they shipped with.

The size of a single board computer can vary widely, but most are far smaller than a typical PC. The earliest such devices, introduced in the late 1970s and early 1980s, were usually found in educational or development computers, and were quite large. Since then, the trend has been towards smaller SBCs, ranging from a little less than the size of a credit card to about the size of Blu-Ray® player. They can come in both standard and nonstandard sizes, and a few are even built to be the same size as a normal PC expansion card or memory module.

Single board computers are commonly housed inside a larger device or product, thereby providing additional intelligence or controlling the functions of machinery or equipment. Automatic teller machines, cash registers, touch screen kiosks, and many other machines and devices often house an embedded single board computer. They are also used in industrial computers and automation equipment, robotics, medical devices, and many other fields. Due to the number of possible uses, SBCs come in a variety of configurations, and many manufacturers build machines tailored to a specific need or industry application.

By the mid 2000s, the cost of computer components had dropped enough to bring the single board computer within reach of the hobbyist community. Several companies now specialize in low-cost yet versatile SBCs for use in amateur electronics and computing projects. These devices may be used on their own to introduce students to computer programming or as part of a larger platform like a robot or interactive art display.

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