Time Based Electrical Appliances Control

Topics: Power supply, Alternating current, Transformer Pages: 29 (8437 words) Published: February 11, 2013

1.1 Introduction to Embedded system
An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions, [1] often 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 control many of the common devices in use today. 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 MP4 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 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.

1.2 Examples of embedded systems

Embedded systems span all aspects of modern life and there are many examples of their use. Telecommunications systems employ numerous embedded systems from telephone switches for the network to mobile phones at the end-user. Computer networking uses dedicated routers and network bridges to route data.

Consumer electronics include personal digital assistants (PDAs), mp3 players, mobile phones,  videogame consoles, digital cameras, DVD players, GPS receivers, and printers. Many household appliances, such as microwave ovens, washing machines and dishwashers, are including embedded systems, these are used to provide flexibility, effiency, accuracy and other features which made human life easier.


2.1 Background of invention
A large variety of electrical appliances are found everywhere. While the presence of those appliances ensures that tasks are performed more safely and efficiently, the effectiveness of those appliances depends on controlling and indicating their operational status. For example, if an appliance is left turned on long after the user has finished with it, careless person may burn themselves on the exposed heated surfaces. Hence, an automatic control for shutting off the appliance as well as for indicating that the appliance has been shut off would avoid this and other safety risks. In addition, the controller/indicator would reduce additional wear and tear on the appliance, as well as save electricity. Another problem created by the absence of indicators or controls stems from the fact that appliances often require a short period of time to reach a ready or operational state. In such instances, the user must periodically test the appliance to see if it is ready. By providing a control circuit for and indicator of a ready state, however, the user avoids losing the time spent testing the appliance. Although some appliances are equipped with control and indicating circuitry that automatically turns the appliance off or indicates that the appliance is ready to use, such circuits have tended to involve relatively complex designs that have not fully solved the problems discussed above. Moreover, the...
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