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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Electronica 2014 München

Electronica 2014 München 

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So what exactly electrical engineering is ?


Electrical engineering is an engineering field that in general studies electricity, electronics and electromagnetism, it also covers their applications The field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraph and electrical power supply.  

It covers a range of subtopics including:
 - Power
 - Electronics
 - Control systems
 - Signal processing
 - Telecommunications

Electrical Engineering is vast as it covers from large-scale electrical systems like power generation and transmission, motor control etc. to very small scale systems including integrated circuits, computers etc. In many countries it is divided as Electrical Engineering (large-scale) and Electronic Engineering (small-scale).

An Electrical Engineer designs methods, devices, technologies etc to make everything simpler for everyone. I said it is the heart of engineering because we design techniques to help other engineering fields work more sufficiently. While designing, we always have to keep in mind how to make the device small (to increase mobility), less power consuming, more efficient, user friendly and last but not the least how to minimize the cost of production.
  
The first Electrical Engineer was  William Gilbert  who designed the versorium ( the first crude electroscope, the first instrument that could detect the presence of static electric charge). There on the numerous achievements in Electrical engineering began. There are plenty of objects, ideas, and concepts which deserve sitting on a list like this but right from the top of my head, I could name some of the obvious candidates, such as (in no particular order…) Electric Battery, Telegraphy, Radio, Television, Radar, Microwave Oven, Diode, Transistors, Integrated Circuits, Microprocessors which presaged the personal computers, cell phones, GPS etc.

If you consider how much of modern life is predicated upon these devices, it is amazing how few people know about most of these, in anything other than an extremely superficial or just a cursory manner… 
Usually people think that an Electrical Engineer is same as an Electrician, who would fix wiring problems or repair broken electronic devices etc. But I hope after reading this post they would be able to differentiate.

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LeCroy raises bar with 100GHz scope

LeCroy raises bar with 100GHz scope

Teledyne LeCroy demonstrated the world’s first 100 GHz real-time oscilloscope on July 24, 2013 at the research facilities of Teledyne Scientific Company in Thousand Oaks, CA. In the demonstration, the prototype scope successfully acquired and displayed live signals at 100 GHz bandwidth. In addition, the Teledyne LeCroy and Teledyne Scientific also unveiled an indium phosphide (InP) chip, which is the first device in a new chip set planned for future generations of high-speed oscilloscopes.

During the demonstration (see video clip below), the injection signal was 100 GHz with a 240 GS/s sample rate (each sample was taken is approximately 4 ps apart). The company’s target applications include CEI-25/28, CEI-56, optical coherent modulation communication systems, defense and radar applications, emerging 10-32 Gb/s serial data technologies, 100GBASE-R Ethernet, SAS12,PCI Express Gen4, Thunderbolt, and next-generation USB.
The demonstration was conducted by Peter J. Pupalaikis, vice president, technology development Teledyne LeCroy; Roger Delbue, vice president, engineering Teledyne LeCroy; and Dr. Amarpal (Paul) Khanna, vice president, components, Phase Matrix, A National Instruments Company.

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Will robots replace humans ?

Just saw an interesting video on youtube (you can watch it below) and it made me think about the possibility, that one day robots will replace us all. I suggest you first watch the video and afterwards would love to hear your opinion about it.

I talked a lot with my friends about this future, where robots will replace humans and we all be unemployed. Most of them told me that is not possible, but I am quite sure that one day this will be real.
I also want to believe that this will not make people poor, but on the contrary, people will thrive. I imagine a day when a robot will replace 3 human workers, but all of these workers will be represented by this robots, therefore they will receive a certain wage. Why would the companies replace all the human workers with robots if nobody will have money to use the services they provide or consume the products they produce?!

Anyways, I wouldn’t like to be replaced by a robot and become a useless “thing” trying to survive everyday without money. Probably, if that day will come, I would probably like to have a piece of land to ensure my basic needs.

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LED - Light Emitting Diode

 

Light Emitting Diodes or LED´s, are among the most widely used of all the different types of semiconductor diodes available today. They are the most visible type of diode, that emit a fairly narrow bandwidth of either visible light at different coloured wavelengths, invisible infra-red light for remote controls or laser type light when a forward current is passed through them.

A Light Emitting Diode or LED as it is more commonly called, is basically just a specialised type of PN Junction diode, made from a very thin layer of fairly heavily doped semiconductor material.

When the diode is forward biased, electrons from the semiconductors conduction band recombine with holes from the valence band releasing sufficient energy to produce photons which emit a monochromatic (single colour) of light. Because of this thin layer a reasonable number of these photons can leave the junction and radiate away producing a coloured light output.

 

 

LED Construction

 

Then we can say that when operated in a forward biased direction Light Emitting Diodes are semiconductor devices that convert electrical energy into light energy.

The construction of a Light Emitting Diode is very different from that of a normal signal diode. The PN Junction of an LED is surrounded by a transparent, hard plastic epoxy resin hemispherical shaped shell or body which protects the LED from both vibration and shock.

Surprisingly, an LED junction does not actually emit that much light so the epoxy resin body is constructed in such a way that the photons of light emitted by the junction are reflected away from the surrounding substrate base to which the diode is attached and are focused upwards through the domed top of the LED, which itself acts like a lens concentrating the amount of light. This is why the emitted light appears to be brightest at the top of the LED.

However, not all LEDs are made with a hemispherical shaped dome for their epoxy shell. Some indication LEDs have a rectangular or cylindrical shaped construction that has a flat surface on top or their body is shaped into a bar or arrow. Also, nearly all LEDs have their cathode, (K) terminal identified by either a notch or flat spot on the body, or by one of the leads being shorter than the other, (the Anode, A).

Unlike normal incandescent lamps and bulbs which generate large amounts of heat when illuminated, the light emitting diode produces a “cold” generation of light which leads to high efficiencies than the normal “light bulb” because most of the generated energy radiates away within the visible spectrum. Because LEDs are solid-state devices, they can be extremely small and durable and provide much longer lamp life than normal light sources.

 

Light Emitting Diode Colours

So how does a light emitting diode get its colour. Unlike normal signal diodes which are made for detection or power rectification, and which are made from either Germanium or Silicon semiconductor materials, Light Emitting Diodes are made from exotic semiconductor compounds such as Gallium Arsenide (GaAs), Gallium Phosphide (GaP), Gallium Arsenide Phosphide (GaAsP), Silicon Carbide (SiC) or Gallium Indium Nitride (GaInN) all mixed together at different ratios to produce a distinct wavelength of colour.

Different LED compounds emit light in specific regions of the visible light spectrum and therefore produce different intensity levels. The exact choice of the semiconductor material used will determine the overall wavelength of the photon light emissions and therefore the resulting colour of the light emitted.

 

Light Emitting Diode colors

Thus, the actual colour of a light emitting diode is determined by the wavelength of the light emitted, which in turn is determined by the actual semiconductor compound used in forming the PN junction during manufacture.

Therefore the colour of the light emitted by an LED is NOT determined by the colouring of the LED’s plastic body although these are slightly coloured to both enhance the light output and to indicate its colour when its not being illuminated by an electrical supply.

Light emitting diodes are available in a wide range of colours with the most common being red, amber, yellow and green and are thus widely used as visual indicators and as moving light displays.

Recently developed blue and white coloured LEDs are also available but these tend to be much more expensive than the normal standard colours due to the production costs of mixing together two or more complementary colours at an exact ratio within the semiconductor compound and also by injecting nitrogen atoms into the crystal structure during the doping process.

From the table above we can see that the main P-type dopant used in the manufacture of Light Emitting Diodes is Gallium (Ga, atomic number 31) and that the main N-type dopant used is Arsenic (As, atomic number 33) giving the resulting compound of Gallium Arsenide (GaAs) crystalline structure.

The problem with using Gallium Arsenide on its own as the semiconductor compound is that it radiates large amounts of low brightness infra-red radiation (850nm-940nm approx.) from its junction when a forward current is flowing through it.

The amount of infra-red light it produces is okay for television remote controls but not very useful if we want to use the LED as an indicating light. But by adding Phosphorus (P, atomic number 15), as a third dopant the overall wavelength of the emitted radiation is reduced to below 680nm giving visible red light to the human eye. Further refinements in the doping process of the PN junction have resulted in a range of colours spanning the spectrum of visible light as we have seen above as well as infra-red and ultra-violet wavelengths.

By mixing together a variety of semiconductor, metal and gas compounds the following list of LEDs can be produced.

Types of Light Emitting Diode

• Gallium Arsenide (GaAs) - infra-red

• Gallium Arsenide Phosphide (GaAsP) - red to infra-red, orange

• Aluminium Gallium Arsenide Phosphide (AlGaAsP) - high-brightness red, orange-red, orange, and yellow

• Gallium Phosphide (GaP) - red, yellow and green

• Aluminium Gallium Phosphide (AlGaP) - green

• Gallium Nitride (GaN) - green, emerald green

• Gallium Indium Nitride (GaInN) - near ultraviolet, bluish-green and blue

• Silicon Carbide (SiC) - blue as a substrate

• Zinc Selenide (ZnSe) - blue

• Aluminium Gallium Nitride (AlGaN) - ultraviolet

Like conventional PN junction diodes, light emitting diodes are current-dependent devices with its forward voltage drop V_F, depending on the semiconductor compound (its light colour) and on the forward biased LED current. The point where conduction begins and light is produced is about 1.2V for a standard red LED to about 3.6V for a blue LED.

The exact voltage drop will of course depend on the manufacturer because of the different dopant materials and wavelengths used. The voltage drop across the LED at a particular current value, for example 20mA, will also depend on the initial conduction V_F point. As an LED is effectively a diode, its forward current to voltage characteristics curves can be plotted for each diode colour as shown below.

Light Emitting Diodes I-V Characteristics

 

Light Emitting Diode (LED) Schematic symbol and I-V Characteristics Curves
showing the different colours available.

 

Before a light emitting diode can “emit” any form of light it needs a current to flow through it, as it is a current dependant device with their light output intensity being directly proportional to the forward current flowing through the LED.

As the LED is to be connected in a forward bias condition across a power supply it should be current limited using a series resistor to protect it from excessive current flow. Never connect an LED directly to a battery or power supply as it will be destroyed almost instantly because too much current will pass through and burn it out.

From the table above we can see that each LED has its own forward voltage drop across the PN junction and this parameter which is determined by the semiconductor material used, is the forward voltage drop for a specified amount of forward conduction current, typically for a forward current of 20mA.

In most cases LEDs are operated from a low voltage DC supply, with a series resistor, R_S used to limit the forward current to a safe value from say 5mA for a simple LED indicator to 30mA or more where a high brightness light output is needed.

 

LED Series Resistance

The series resistor value R_S is calculated by simply using Ohm's Law, by knowing the required forward current I_F of the LED, the supply voltage V_S across the combination and the expected forward voltage drop of the LED, V_F at the required current level, the current limiting resistor is calculated as:

 

LED Series Resistor Circuit

 

 

Light Emitting Diode Example

An amber coloured LED with a forward volt drop of 2 volts is to be connected to a 5.0v stabilised DC power supply. Using the circuit above calculate the value of the series resistor required to limit the forward current to less than 10mA. Also calculate the current flowing through the diode if a 100Ω series resistor is used instead of the calculated first.

1. series resistor required at 10mA.

 

 

 

2. with a 100Ω series resistor.

 

 

 

We remember from the Resistors tutorials, that resistors come in standard preferred values. Our first calculation above shows that to limit the current flowing through the LED to 10mA exactly, we would require a 300Ω resistor. In the E12 series of resistors there is no 300Ω resistor so we would need to choose the next highest value, which is 330Ω. A quick re-calculation shows the new forward current value is now 9.1mA, and this is ok.

 

Connecting LEDs Together in Series

We can connect LED’s together in series to increase the number required or to increase the light level when used in displays. As with series resistors, LED’s connected in series all have the same forward current, I_F flowing through them as just one. As all the LEDs connected in series pass the same current it is generally best if they are all of the same colour or type.

LED’s in Series

 

Although the LED series chain has the same current flowing through it, the series voltage drop across them needs to be considered when calculating the required resistance of the current limiting resistor, R_S. If we assume that each LED has a voltage drop across it when illuminated of 1.2 volts, then the voltage drop across all three will be 3 x 1.2v = 3.6 volts.

If we also assume that the three LEDs are to be illuminated from the same 5 volt logic device or supply with a forward current of about 10mA, the same as above. Then the voltage drop across the resistor, R_S and its resistance value will be calculated as:

 

 

 

Again, in the E12 (10% tolerance) series of resistors there is no 140Ω resistor so we would need to choose the next highest value, which is 150Ω.

 

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A Diode

Diode, an electrical component that allows the flow of current in only one direction. In circuit diagrams, a diode is represented by a triangle with a line across one vertex.

The most common type of diode uses a p-n junction. In this type of diode, one material (n) in which electrons are charge carriers abuts a second material (p) in which holes (places depleted of electrons that act as positively charged particles) act as charge carriers. At their interface, a depletion region is formed across which electrons diffuse to fill holes in the p-side. This stops the further flow of electrons. When this junction is forward biased (that is, a positive voltage is applied to the p-side), electrons can easily move across the junction to fill the holes, and a current flows through the diode. When the junction is reverse biased (that is, a negative voltage is applied to the p-side), the depletion region widens and electrons cannot easily move across. The current remains very small until a certain voltage (the breakdown voltage) is reached and the current suddenly increases.

(A) Current-voltage characteristics of a typical silicon p-n junction. (B) Forward-bias and (C) reverse-bias conditions. (D) The symbol for a p-n junction.

Light-emitting diodes (LEDs) are p-n junctions that emit light when a current flows through them. Several p-n junction diodes can be connected in series to make a rectifier (an electrical component that converts alternating current to direct current). Zener diodes have a well-defined breakdown voltage, so that current flows in the reverse direction at that voltage and a constant voltage can be maintained despite fluctuations in voltage or current. In varactor (or varicap) diodes, varying the bias voltage causes a variation in the diode’s capacitance; these diodes have many applications for signal transmission and are used throughout the radio and television industries.

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