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 lowcost, easytointe-
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.
+
R
VSUPPLY
RSENSOR
CALIBRATION
RESISTOR
P15
P13
TH
LOW BATTERY
DETECTION
ALARM IC
LED
PIEZOHORN
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 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.
Figure 2. Temperature Level Example
+
R
VSUPPLY
P15
P13
TH
LOW BATTERY
DETECTION
ALARM IC
LED
PIEZOHORN
LOGICAL
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AN4009
2
WATER LEVEL DETECTOR
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 be-
tween the detection pin and the supply drops from an open cir-
cuit 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 monitor-
ing system allowing pump starting, floodgate closing and oth-
ers. This simple system is useful for numerous applications,
such as swimming pool water level alarms, defrosting water
level detectors, and inhouse flood alarms.
+
VSUPPLY
PROBE
P15
P13
LOW BATTERY
DETECTION
ALARM IC
LED
PIEZOHORN
LOGICAL
Figure 3. WaterLevel Detection Example
MOTION INDICATOR
The Alarm IC can be used to detect motion and can be inte-
grated 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 accel-
erometer, 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
flipflop connected to pin 15 of the Alarm IC. The alarm is trig-
gered and will continue on until a new movement is detected,
resetting the counter.
+
VSUPPLY
LOW G
ACCELEROMETER
P15
LOW BATTERY
DETECTION
ALARM IC
LED
PIEZOHORN
LOGICAL
Figure 4. Motion Indicator Example
LOGIC
BLOCK
COUNTER
GATES
FLIPFLOP
+
INCLUDING
FILTER MONITOR
An ideal solution for air cleanliness control is provided when
the Alarm IC is directly connected to an MPX5000 series pres-
sure sensor. This sensor family is compensated in tempera-
ture 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 compara-
tor is triggered.
+
VSUPPLY
MPX5XXX
SERIES
P15
P13
LOW BATTERY
DETECTION
ALARM IC
LED
PIEZOHORN
LOGICAL
Figure 5. Pressure Change (Filter) Example
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AN4009
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For More Information On This Product,
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