AN4009 Datasheet, PDF (1/4 Pages) Freescale Semiconductor, Inc – ALARM IC SAMPLE APPLICATIONS

Freescale Semiconductor
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Alarm IC Sample Applications
Prepared by: Rudi Lenzen
Application Engineer, Toulouse France
AN4009
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–inte-
grate 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 pur-
pose 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 detec-
tion.
When gas leakage is detected, the sensing resistor de-
creases typically by a factor 3 or 4 as the gas concentration
reaches 10 percent of the lower explosive limit. During the cal-
ibration sequence (test under gas), a variable resistor is used
to set the trigger level of the Alarm IC comparator which, in re-
sponse, drives a piezo horn.
By adding a thermistor—with negative temperature coeffi-
cient (NTC) in this case—in the detection circuit, the variation
of the sensor resistance with temperature is easily compen-
sated, avoiding false alarms when the room temperature in-
creases.
VSUPPLY
CALIBRATION
RTH
RESISTOR
RSENSOR
P15
+
–
P13
ALARM IC
LED
PIEZO–HORN
LOGICAL
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 bat-
tery comparator indicating the state of the power supply.
TEMPERATURE LEVEL DETECTOR
When connected to a simple network of thermistor and re-
sistors, the Alarm IC provides a portable solution for tempera-
ture 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 start-
ing either a fan or a heater depending upon the required tem-
perature.
VSUPPLY
RTH
ALARM IC
P15
+
–
P13
LED
PIEZO–HORN
LOGICAL
LOW BATTERY
DETECTION
Figure 2. Temperature Level Example
LOW BATTERY
DETECTION
Figure 1. Gas Detection Example
© Freescale Semiconductor, Inc., 2004. All rights reserved.
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