Page 404 - Understanding Automotive Electronics

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FUTURE AUTOMOTIVE ELECTRONIC SYSTEMS 11

a multiplexing system. In a system of this type, a remote switch applies battery
power to the component when activated by the receiver module (RM). The
receiver module is activated by a command from the CPU that is transmitted
along the control signal bus.
A multiplexed system This control signal bus operates very much like the sensor data bus
can also control switch- described in the multiplexed engine control system. The particular
ing of electrical power component to be switched is initially selected by switches operated by the
for lights, motors, and driver. (Of course, these switches can be multiplexed at the input of the
similar devices. Each CPU.) The CPU sends an RM address as a sequence of binary pulses along
RM would switch power the control signal bus. Each receiver module responds only to one particular
to the appropriate device address. Whenever the CPU is to turn a given component on or off, it
in response to a CPU transmits the coded address and command to the corresponding RM. When
command. the RM receives its particular code, it operates the corresponding switch,
either applying battery power or removing battery power, depending on the
command transmitted by the CPU.
Fiber Optics

Signal buses using fiber It is possible, maybe even desirable, to use an optical fiber for the signal
optics transmit data and bus. For such a system, the address voltage pulses from the CPU are
control signals in the converted to corresponding pulses of light that are transmitted over an
form of light pulses optical fiber. An optical fiber, which is also known as a light pipe, consists of a
along thin fiber “wires.” thin transparent cylinder of light-conducting glass about the size of a human
Such systems are rela- hair. Light will follow the light pipe along its entire path, even around
tively immune from corners, just as electricity follows the path of wire. A big advantage of the
noise interference. optical fiber signal bus for automotive use is that external electrical noise
doesn’t interfere with the transmitted signal. The high-voltage pulses in the
ignition circuit, which are a major potential source of interference in
automotive electronic systems, will not affect the signals traveling on the
optical signal bus.
For such a system, each component has an RM that has an optical
detector coupled to the signal bus. Each detector receives the light pulses that
are sent along the bus. Whenever the correct sequence (i.e., address) is received
at the RM, the corresponding switch is either closed or opened.
A variety of multiplexing systems have been experimentally studied. It
seems very likely that one form or another of multiplexing system will be used
in the near future whenever the cost of such a system becomes less than that of
the harness that it is to replace. It is possible that the move to multiplexing will
occur in stages. For example, one experimental system incorporates a
multiplexing system for switches located in the door only.

NAVIGATION
One of the more interesting potential future developments in the
application of electronics to automobiles is navigation. Every driver who has

UNDERSTANDING AUTOMOTIVE ELECTRONICS 391