MPXM2102AS datasheet(114/670 Pages) MOTOROLA

114 / 670 page

AN1612

2–78

Motorola Sensor Device Data

www.motorola.com/semiconductors

100 k

+5.0 V

1 5

+5.0 V

100 k

1.0

–

LM311N

VOUT

VIN

VREF

Figure 3. Comparator Circuitry

For instance, if the threshold level is to be set to –20g, this

will correspond to a Vref voltage of 1.7 V.

REF + VOFFSET )

THRESHOLD

+ 2.5 ) (0.04

[

* 20])

+ 1.7 V

Under normal condition, Vin (which is the output of the

accelerometer) is at about 2.5V. Since Vin is higher than Vref,

the output of the comparator is at logic “0”. During any shock

or impact which is greater than –20g in magnitude, the output

voltage of the accelerometer will go below Vref. In this case,

the output logic of the comparator changes from “0” to “1”.

When the pager is in silence mode, the vibrator produces an

output of about

±2g. This will not trigger the comparator.

Therefore, even in silence mode, the user can also tap the

pager to stop the alert. Refer to Figure 5 for the vibrator

waveform.

– 0.05

– 0.03

– 0.01

0.01

0.03

0.05

1.0

2.0

3.0

4.0

5.0

6.0

TIME (seconds)

Figure 4. Comparator Output Waveform

– 0.025

– 0.015

– 0.005

0.005

0.015

0.025

– 2.0

–1.5

–1.0

– 0.5

1.5

2.0

TIME (seconds)

0.5

1.0

Figure 5. Vibrator Waveform

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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