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Motorola Sensor Device Data
For More Information On This Product,
Go to: www.freescale.com
Prepared by: Jeff Baum
Discrete Applications Engineering
INTRODUCTION
Typically, a semiconductor pressure transducer converts
applied pressure to a “l(fā)ow–level” voltage signal. Current
technology enables this sensor output to be temperature
compensated and amplified to higher voltage levels on a
single silicon integrated circuit (IC). While on–chip
temperature compensation and signal conditioning certainly
provide a significant amount of added value to the basic
sensing device, one must also consider how this final output
will be used and/or interfaced for further processing. In most
sensing systems, the sensor signal will be input to additional
analog circuitry, control logic, or a microcontroller unit (MCU).
MCU–based systems have become extremely cost
effective. The level of intelligence which can be obtained for
only a couple of dollars, or less, has made relatively simple
8–bit microcontrollers the partner of choice for semiconductor
pressure transducers. In order for the sensor to communicate
its pressure–dependent voltage signal to the microprocessor,
the MCU must have an analog–to–digital converter (A/D) as
an on–chip resource or an additional IC packaged A/D. In the
latter case, the A/D must have a communications interface
that is compatible with one of the MCU’s communications
protocols. MCU’s are adept at detecting logic–level transitions
that occur at input pins designated for screening such events.
As an alternative to the conventional A/D sensor/MCU
interface, one can measure either a period (frequency) or
pulse width of an incoming square or rectangular wave signal.
Common MCU timer subsystem clock frequencies permit
temporal measurements with resolution of hundreds of
nanoseconds. Thus, one is capable of accurately measuring
the the frequency output of a device that is interfaced to such
a timer channel. If sensors can provide a frequency modulated
signal that is linearly proportional to the applied pressure
being measured, then an accurate, inexpensive (no A/D)
MCU–based sensor system is a viable solution to many
challenging sensing applications. Besides the inherent cost
savings of such a system, this design concept offers additional
benefits to remote sensing applications and sensing in
electrically noisy environments.
Figure 1. DEVB160 Frequency Output Sensor EVB
(Board No Longer Available)
SEMICONDUCTOR APPLICATION NOTE
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