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TAMPERATURE BASED FAN SPEED CONTROLLER

INTRODUCTION

Embedded systems are finding increasing application not only in domestic applications but also in areas of industrial automation, automobiles, power electronics, defence and space equipments. Micro controllers are the basic building blocks for many embedded systems. In spite of revolutionary advances in the field of electronics, micro controllers play a major role in the design of embedded control systems during the past two decades. They are available in 8-bit, 16-bit and 32-bit versions and are manufactured by a number of leading companies like Intel, Motorola, Philips, Hitachi, Atmen, Microchip, Dallas, Siemens etc., . They are available in the market with various configurations for different applications.


1 How the data is collected?
Sensors are used to input the data into the data-logging equipment. Almost any physical property can be measured with the correct sensor. The data logger collects the data at regular intervals (the logging interval) for a set length of time (the logging period).There are two categories of sensors: Digital sensors - these are either on or off i.e. a light gate sensing something breaking a light beam. Such sensors can often be connected directly to a computer as the data output is already digital Analog sensors - these measure some physical quantity by converting it into a voltage. The voltage signal is then converted into digital form by an interface and either stored or transferred directly to a computer. The vast majority of sensors are of this type.
1.2 How the data is stored?
The data that is logged is usually stored in RAM memory or on some form of backing storage as it is collected .Some data-logging equipment is designed to be linked directly to a computer (this could be a wireless link). This would be suitable if an experiment is taking place in the laboratory for example .If you wanted to record data out in the field then battery powered data-logging equipment would be needed that could measure and store the data until the unit is collected. The equipment would then be connected to a computer so the data can be down-loaded. This data collection could still be done out in the field if a portable computer was used to collect the data. 1.3 How the data can be displayed? Once downloaded to a computer, the different types of data and are display it more clearly by the hyper terminal.
2.1 INTRODUCTION TO EMBEDDED SYSTEM

2.1.1 EMBEDDED SYSTEM

An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions, sometimes with real-time computing constraints. It is usually embedded as part of a complete device including hardware and mechanical parts. In contrast, a general-purpose computer, such as a personal computer, can do many different tasks depending on programming. Embedded systems have become very important today as they control many of the common devices we use. Since the embedded system is dedicated to specific tasks, design engineers can optimize it, reducing the size and cost of the product, or increasing the reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale. Physically, embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, or the systems controlling nuclear power plants. Complexity varies from low, with a single microcontroller chip, to very high with multiple units, peripherals and networks mounted inside a large chassis or enclosure. In general, "embedded system" is not an exactly defined term, as many systems have some element of programmability. For example, Handheld computers share some elements with embedded systems — such as the operating systems and microprocessors which power them — but are not truly embedded systems, because they allow different applications to be loaded and peripherals to be connected. An embedded system is some combination of computer hardware and software, either fixed in capability or programmable, that is specifically designed for a particular kind of application device. Industrial machines, automobiles, medical equipment, cameras, household appliances, airplanes, vending machines, and toys (as well as the more obvious cellular phone and PDA) are among the myriad possible 6 hosts of an embedded system. Embedded systems that are programmable are provided with a programming interface, and embedded systems programming is a specialized occupation. Certain operating systems or language platforms are tailored for the embedded market, such as Embedded Java and Windows XP Embedded. However, some lowend consumer products use very inexpensive microprocessors and limited storage, with the application and operating system both part of a single program. The program is written permanently into the system's memory in this case, rather than being loaded into RAM (random access memory), as programs on a personal computer.
2.1.2 MICROCONTROLLERS FOR EMBEDDED SYSTEMS
In the Literature discussing microprocessors, we often see the term Embedded System. Microprocessors and Microcontrollers are widely used in embedded system products. An embedded system product uses a microprocessor (or Microcontroller) to do one task only. A printer is an example of embedded system since the processor inside it performs one task only; namely getting the data and printing it. Contrast this with a Pentium based PC. A PC can be used for any number of applications such as word processor, print-server, bank teller terminal, Video game, network server, or Internet terminal. Software for a variety of applications can be loaded and run. Of course the reason a pc can perform myriad tasks is that it has RAM memory and an operating system that loads the application software into RAM memory and lets the CPU run it. In an Embedded system, there is only one application software that is typically burned into ROM. An x86 PC contains or is connected to various embedded products such as keyboard, printer, modem, disk controller, sound card, CD-ROM drives, mouse, and so on. Each one of these peripherals has a Microcontroller inside it that performs only one task. For example, inside every mouse there is a Microcontroller to perform the task of finding the mouse position and sending it to the PC. Table 1-1 lists some embedded products.
2.2 8051 ARCHITECTURE
The generic 8051 architecture supports a Harvard architecture, which contains two separate buses for both program and data. So, it has two distinctive memory spaces of 64K X 8 size for both programmed and data. It is based on an 8 bit central processing unit with an 8 bit Accumulator and another 8 bit B register as main processing blocks. Other portions of the architecture include few 8 bit and 16 bit registers and 8 bit memory locations. Each 8051 device has some amount of data RAM built in the device for internal processing. This area is used for stack operations and temporary storage of data. This bus architecture is supported with on-chip peripheral functions like I/O ports, timers/counters, versatile serial communication port. So it is clear that this 8051 architecture was designed to cater many real time embedded needs.