Page 331 - Understanding Automotive Electronics

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9 AUTOMOTIVE INSTRUMENTATION

susceptibility to failure due to vibration and mechanical shock. However, this
problem can be reduced by mounting the display on a shock-absorbing
isolation mount.

CRT
The display devices that have been discussed to this point have one rather
serious limitation. The characters that can be displayed are limited to those
symbols that can be approximated by the segments that can be illuminated.
Furthermore, illuminated warning messages such as “Check Engine” or “Oil
Pressure” are fixed messages that are either displayed or not, depending on the
engine conditions. The primary disadvantage of such ad hoc display devices is
the limited flexibility of the displayed messages.
The cathode ray tube The display device that has the greatest flexibility for displaying messages
(CRT) is similar to a TV or pictorial information is the cathode ray tube (CRT). The CRT that is
picture tube and has perhaps most familiar to the reader is the television picture tube. The CRT is
great potential for auto- also the display device most commonly used in personal computers.
motive display applica- A technology that has the same flexibility of display as the CRT is the
tions. solid-state equivalent of a CRT. Such a display is commonly called a flat-panel
display. Such a display, if it can be produced at sufficiently low cost, has
enormous potential in future automotive IP displays. However, as it is
functionally equivalent to the CRT and as the CRT is an existing, very mature
technology, we will describe such displays using the CRT example.
The CRT is being used increasingly for display purposes in the aerospace
industry, where it is used to display aircraft attitude information (sometimes
pictorially), aircraft engine or airframe parameters, navigational data, and
warning messages. Clearly, the CRT has great potential for automotive
instrumentation display.
It has, however, certain disadvantages compared to solid-state or
electromechanical display devices. For example, its size and shape make it
complicated to locate in the instrument panel, where it can most easily be read
by the driver. In addition, the CRT requires circuitry for its operation that is
not required by a solid-state digital display. Furthermore, the CRT is more
expensive than a typical solid-state or vacuum-fluorescent display. The
hardware cost incurred for a CRT is essentially independent of the complexity
of displayed messages, whereas the cost of alternate solid-state or vacuum-
fluorescent displays increases somewhat with complexity of the messages. Thus,
the cost of the CRT only becomes comparable with vacuum-fluorescent
displays as message complexity increases.
Although there have been numerous experimental and a few
commercially successful automotive CRT display systems, the future of this
application is uncertain. However, it is worthwhile to describe the technology
to give the reader some insight into the varied potential automotive
instrumentation applications. While it is beyond the scope of this book to
explain in detail the physical processes of the CRT and its associated electronic

318 UNDERSTANDING AUTOMOTIVE ELECTRONICS