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Many devices connected to a local area net-work (LAN) are left on continuously, even  when they are not needed, including DSL  and cable modems, routers, wireless access  points, networked hard drives, printer servers and printers. The power consumption of  all these devices can add up to a considerable  fraction of one’s electricity bill. With the simple circuit described here we can ensure that  all these devices are only powered up when  at least one selected host device (such as a PC  or a streaming media client) is turned on. We insert a relay in the mains supply to the  devices whose power is to be switched, along  with a driver circuit controlled from the host  device over a two-wire bus. Optocouplers  provide galvanic isolation. One way to implement the bus is to use the spare pair of conductors that is often available in the existing  LAN cable.   The circuit diagram shows an example con-figuration where there are two controlling  host devices (a streaming media client and a...

Entertainment in the form of music, news or even movies, generated from a series of audio devices found in a car. The series device known as a car audio system. What tool or device contained in car audio system? Car Head Unit - Head unit is the core of a car audio system, part of the car audio system that plays sound. The continued development of technology makes the head unit is no longer only serve as a radio receiver FM / AM CD player and a player, some have additional functions to be able to play MP3s. There is also a car head unit that has the ability to play DVDs complete with monitors and can be connected with IPOD. Power Amplifier - The function of the power amplifier is to amplify the signal coming out of the head unit. In the world of various types of car audio power amplifiers are divided into several classes, such as class A, B, AB, and D. Each class power amplifier has the advantage that its usefulness can be tailored to our needs in building a car audio system. In additio...