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Comparator Alarms Circuits
Designed by David A. Johnson, P.E.

Last Updated on: Friday, July 18, 2008 11:34 AM

Master Category List - Dave's Circuits
 
  • ACCEPTABLE VOLTAGE INDICTOR
    I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed.  The circuit can also be used to adjust a particular voltage be within specific high or low limits.  The three LEDs will indicate if the voltage is high, low or OK.  When connected to other converters, such as a frequency to voltage converter, a current to voltage converter or a power to voltage meter, it could provide a quick indication of a proper level.

  • PRECISION AC PEAK DETECTOR
    This unique circuit uses a very inexpensive voltage comparator to form a peak detector. The DC voltage produced tracks the positive peak of the input signal.  It works from about ten millivolts to about 10 volts peak to peak.  The maximum frequency is about 150KHz.
  • WIDE BAND ZERO CROSS DETECTOR
    This circuit was designed to convert a low amplitude 40KHz signal into a clean square wave signal.  It will work with inputs as small as 5mv peak-to-peak or as large as 3 volts peak to peak.  The input frequency can range from a few kilohertz to about 150KHz.
  • XENON LAMP FLASH DETECTOR
    This circuit uses a small 2.5mm square photo diode in conjunction with a 100mH coil to detect the short light flashes from a xenon lamp.  The coil makes the circuit immune to normal room lights.  Its 10mv sensitivity can detect light flashes from a range of over 100 feet.  Reflections from a room’s walls and ceiling is usually enough to trigger the circuit.  The entire circuit draws only 3 Microamps from a 6 to 9 volt battery.


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