MPXM2102AS datasheet(409/670 Pages) MOTOROLA

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Motorola Sensor Device Data

www.motorola.com/semiconductors

AN1316

FrequencyOutput Conversion for MPX2000

Series Pressure Sensors

Prepared by: Jeff Baum

Discrete Applications Engineering

INTRODUCTION

Typically, a semiconductor pressure transducer converts

applied pressure to a “low–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)

MOTOROLA

SEMICONDUCTOR APPLICATION NOTE

REV 2

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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