MPXM2102AS datasheet(424/670 Pages) MOTOROLA

424 / 670 page

AN1318

3–278

Motorola Sensor Device Data

www.motorola.com/semiconductors

DIRECT INTERFACE

WITH INTEGRATED SENSORS

The simplest interface is achieved with an integrated sensor

and a microcomputer that has an on–chip A/D converter.

Figure 10 shows an LCD pressure gauge that is made with an

MPX5100 integrated sensor and MC68HC05 microcomputer.

Although the total schematic is reasonably complicated, the

interface between the sensor and the micro is a single wire.

The MPX5100 has an internal amplifier that outputs a 0.5 to

4.5 V signal that inputs directly to A/D port PD5 on the HC05.

The software in this system is written such that the

processor assumes zero pressure at power up, reads the

sensor’s output voltage, and stores this value as zero

pressure offset. Full scale span is adjustable with jumpers J1

and J2. For this particular system the software is written such

that with J1 out and J2 in, span is decreased by 1.5%. Similarly

with J1 in and J2 out, span is increased by 1.5%. Given the

2.5% full scale spec on the sensor, these jumpers allow

calibration to

± 1% without the use of pots.

MIX AND MATCH

The circuits that have been described so far are intended to

be used as functional blocks. They may be combined in a

variety of ways to meet the particular needs of an application.

For example, the Frequency Output Pressure Sensor in

Figure 8 uses the sensor interface circuit described in Figure

4 to provide an input to the voltage–to–frequency converter.

Alternately, an MPX5100 could be directly connected to pin 4

of the AD654 or the output of Figure 3’s

Precision

Instrumentation Amplifier Interface could by substituted in the

same way. Similarly, the Pressure Gauge described in Figure

10 could be constructed with any of the interfaces that have

been described.

CONCLUSION

The circuits that have been shown here are intended to

make interfacing semiconductor pressure sensors to digital

systems easier. They provide cost effective and relatively

simple ways of interfacing sensors to microcomputers. The

seven different circuits contain many tradeoffs that can be

matched to the needs of individual applications. When

considering these tradeoffs it is important to throw software

into the equation. Techniques such as automatic zero

pressure calibration can allow one of the inexpensive analog

interfaces to provide performance that could otherwise only be

obtained with a more costly precision interface.

REFERENCES

1. Baum, Jeff, “Frequency Output Conversion for

MPX2000 Series Pressure Sensors,” Motorola Applica-

tion Note AN1316/D.

2. Lucas, William, “An Evaluation System for Direct Inter-

face of the MPX5100 Pressure Sensor with a Micropro-

cessor,” Motorola Application Note AN1305.

3. Lucas, William, “An Evaluation System for Interfacing the

MPX2000 Series Pressure Sensors to a Microproces-

sor,” Motorola Application Note AN1315.

4. Schultz, Warren, “Compensated Sensor Bar Graph

Pressure Gauge,” Motorola Application Note AN1309.

5. Schultz, Warren, “Interfaced Sensor Evaluation Board,”

Motorola Application Note AN1312.

6. Schultz, Warren, “Sensor Building Block Evaluation

Board,” Motorola Application Note AN1313.

7. Williams, Denise, “A Simple 4–20 mA Pressure Trans-

ducer Evaluation Board,” Motorola Application Note

AN1303.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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