MPXM2102AS datasheet(662/670 Pages) MOTOROLA

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Motorola Sensor Device Data

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AN4009

Alarm IC Sample Applications

Prepared by: Rudi Lenzen

Application Engineer, Toulouse France

INTRODUCTION

The MC14600 is an integrated circuit (IC) designed for

low–cost applications requiring an alarm to be triggered and

heard. This device affords the designer a low–cost,

easy–to–integrate solution, where board space and design

time are at a premium. The Alarm IC can be used in multiple

applications, such as personal, home and auto safety/security

devices; door, gate and pool alarms; and even toys, where

lasers and motion are employed, for example. However, this

paper’s purpose is to introduce you to just a few applications

for which the MC14600 is a perfect fit.

GAS SENSOR APPLICATION

The MC14600, used with a flammable gas sensor and a few

added components, provides a reliable solution for gas

detection.

When gas leakage is detected, the sensing resistor

decreases typically by a factor 3 or 4 as the gas concentration

reaches 10 percent of the lower explosive limit. During the

calibration sequence (test under gas), a variable resistor is

used to set the trigger level of the Alarm IC comparator which,

in response, drives a piezo horn.

By adding a thermistor—with negative temperature

coefficient (NTC) in this case—in the detection circuit, the

variation of the sensor resistance with temperature is easily

compensated, avoiding false alarms when the room

temperature increases.

–

VSUPPLY

RSENSOR

CALIBRATION

RESISTOR

P15

P13

LOW BATTERY

DETECTION

ALARM IC

LED

PIEZO–HORN

LOGICAL

Figure 1. Gas Detection Example

The logical output is useful to signal a remote control station

that a gas leakage has been detected.

When using a low power sensor, the circuit is fully compliant

with a portable solution enhanced by the integrated low

battery comparator indicating the state of the power supply.

TEMPERATURE LEVEL DETECTOR

When connected to a simple network of thermistor and

resistors, the Alarm IC provides a portable solution for

temperature control and supervision. The example hereafter

uses an NTC thermistor.

An audible alarm will sound when the threshold value at the

comparator input is reached. A logic output is usable for

starting either a fan or a heater depending upon the required

temperature.

Figure 2. Temperature Level Example

–

VSUPPLY

P15

P13

LOW BATTERY

DETECTION

ALARM IC

LED

PIEZO–HORN

LOGICAL

MOTOROLA

SEMICONDUCTOR TECHNICAL DATA

REV 0

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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