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Motorola Sensor Device Data
www.motorola.com/semiconductors
Go to: www.freescale.com
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.
–
+
R
VSUPPLY
RSENSOR
CALIBRATION
RESISTOR
P15
P13
TH
LOW BATTERY
DETECTION
ALARMIC
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
–
+
R
VSUPPLY
P15
P13
TH
LOW BATTERY
DETECTION
ALARMIC
LED
PIEZO–HORN
LOGICAL
SEMICONDUCTOR TECHNICAL DATA
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Freescale Semiconductor, Inc.
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