MPXV2202DP datasheet(514/670 Pages) MOTOROLA

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Motorola Sensor Device Data

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AN1586

Designing a Homemade Digital Output for

Analog Voltage Output Sensors

by: Eric Jacobsen

Systems and Applications Engineer

Sensor Products Division

Motorola, Inc.

A digital output is more desirable than an analog output in

noisy environments (e.g. automotive, washing machines,

etc.) and remote sensing applications (building controls,

industrial applications, etc.) because a digital signal inherently

has better noise immunity compared to analog signals.

Additional applications requiring a sensor with a digital output

include microcontroller–based systems that have no A/D in

the system or that have no A/D channels available for the

sensing function. For these applications, there is no other

option but a digital output to further process the signal.

Via a design example this paper shows how to easily

convert an analog voltage output sensor to a digital output

sensor. For the design example, each of the required circuit

components is discussed in detail. While the design is

applicable to analog voltage output sensors (differential or

single–ended output) in general, the design example and

following

discussions

will

pertain

specifically

semiconductor pressure sensors.

The digital output sensor in Figure 1.

consists of the

following:

• Motorola MPX2000 series pressure sensor

• A two op amp gain stage to amplify the sensor’s signal

• An integrator (i.e. a low pass filter consisting of one resistor

and one capacitor)

• An LM311 comparator

• An MC68HC05P9 microcontroller with which only two pins

are used: the output compare timer channel (TCMP) and

one general I/O pin (the input capture timer channel, TCAP,

can be used in place of the general I/O pin). Since only two

of the MC68HC05P9’s pins are used, the remaining pins

are available for other system functions.

Figure 1. The Digital Output Sensor Schematic

AMPLIFIER

COMPARATOR

INTEGRATOR

TO MC68HC05P9’s

GENERAL I/O PIN OR

TCAP PIN

PRESSURE SENSOR

–

FROM MC68HC05P9’s

TCMP PIN

–

+5 V

MC33272

+5 V

LM311

R+SHIFT1

R+SHIFT2

+5 V

MPX2000

SERIES

+5 V

(OPTIONAL)

MOTOROLA

SEMICONDUCTOR APPLICATION NOTE

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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