AN4009 Alarm IC Sample Applications

AN4009 Alarm IC Sample Applications
Freescale Semiconductor
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AN4009
Alarm IC Sample Applications
Prepared by: Rudi Lenzen
Application Engineer, Toulouse France
Freescale Semiconductor, Inc...
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.
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.
V SUPPLY
ALARM IC
R TH
LED
P15
+
–
P13
PIEZO–HORN
LOGICAL
LOW BATTERY
DETECTION
V SUPPLY
CALIBRATION
RESISTOR
RSENSOR
R TH
ALARM IC
Figure 2. Temperature Level Example
LED
P15
+
–
PIEZO–HORN
P13
LOGICAL
LOW BATTERY
DETECTION
Figure 1. Gas Detection Example
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WATER LEVEL DETECTOR
FILTER MONITOR
A single probe connected directly on the detection pin of the
Alarm IC provides a portable solution for water level detection.
When liquid enters in contact with the probe, the resistor between the detection pin and the supply drops from an open circuit to a measurable value. With an appropriate choice of
bridge resistors, the presence of liquid will trigger the
comparator. The logic level can be connected to any monitoring system allowing pump starting, floodgate closing and others. This simple system is useful for numerous applications,
such as swimming pool water level alarms, defrosting water
level detectors, and in–house flood alarms.
An ideal solution for air cleanliness control is provided when
the Alarm IC is directly connected to an MPX5000 series pressure sensor. This sensor family is compensated in temperature and has its output signal directly exploitable (internally
amplified). Therefore, the sensor can be connected to the
detection pin of the circuit without any additional component.
When a certain level of dust affects the efficiency of the filter,
a differential pressure is measured and the Alarm IC comparator is triggered.
ALARM IC
V SUPPLY
V SUPPLY
LED
ALARM IC
MPX5XXX
SERIES
P15
PROBE
+
–
+
–
P13
PIEZO–HORN
P13
PIEZO–HORN
LOGICAL
LOGICAL
LOW BATTERY
DETECTION
LOW BATTERY
DETECTION
Figure 5. Pressure Change (Filter) Example
Figure 3. Water–Level Detection Example
MOTION INDICATOR
The Alarm IC can be used to detect motion and can be integrated into products, such as an ordinary clothes iron, where
this is critical. Used with a low G accelerometer and a few logic
components, the device can signal the user that there is a risk
of clothes burning during use and that the iron must be shut
off from the AC power after use. At the output of the accelerometer, a simple peak detection circuit is required to keep
the signal active long enough.
When no movement is detected, the output comparator is
low and the counter starts. A first “beep” is heard after a few
seconds to advise that there is a risk of clothes burning. If no
movement is detected, the counting continues and drives a
flip–flop connected to pin 15 of the Alarm IC. The alarm is triggered and will continue on until a new movement is detected,
resetting the counter.
V SUPPLY
LOW G
ACCELEROMETER
Freescale Semiconductor, Inc...
LED
P15
+
–
ALARM IC
LOGIC
BLOCK
INCLUDING
COUNTER
GATES
FLIP–FLOP
LED
P15
+
–
PIEZO–HORN
LOGICAL
LOW BATTERY
DETECTION
Figure 4. Motion Indicator Example
2
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AN4009
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NOTES
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