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 thermistorewith negative temperature coeffi- cient (ntc) in this caseein 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 v supply r sensor 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 v supply p15 p13 th low battery detection alarm ic led piezohorn logical order this document by AN4009/d f r e e s c a l e s e m i c o n d u c t o r , i f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
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. + v supply 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 abeepo 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. + v supply 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. + v supply mpx5xxx series p15 p13 low battery detection alarm ic led piezohorn logical figure 5. pressure change (filter) example f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
3 notes f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. f o r m o r e i n f o r m a t i o n o n t h i s p r o d u c t , g o t o : w w w . f r e e s c a l e . c o m n c . . .
f r e e s c a l e s e m i c o n d u c t o r , i freescale semiconductor, inc. n c . . .
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