| In the design of large and complex digital 
    systems, it is often necessary to have one device communicate digital 
    information to and from other devices. One advantage of digital information 
    is that it tends to be far more resistant to transmitted and interpreted 
    errors than information symbolized in an analog medium. This accounts for 
    the clarity of digitally-encoded telephone connections, compact audio disks, 
    and for much of the enthusiasm in the engineering community for digital 
    communications technology. However, digital communication has its own unique 
    pitfalls, and there are multitudes of different and incompatible ways in 
    which it can be sent. Hopefully, this chapter will enlighten you as to the 
    basics of digital communication, its advantages, disadvantages, and 
    practical considerations.
     Suppose we are given the task of remotely monitoring the level of a water 
    storage tank. Our job is to design a system to measure the level of water in 
    the tank and send this information to a distant location so that other 
    people may monitor it. Measuring the tank's level is quite easy, and can be 
    accomplished with a number of different types of instruments, such as float 
    switches, pressure transmitters, ultrasonic level detectors, capacitance 
    probes, strain gauges, or radar level detectors.  >>Know 
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