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Security and alarm system employing a particular pulse width discriminator

  • US 4,847,577 A
  • Filed: 11/17/1987
  • Issued: 07/11/1989
  • Est. Priority Date: 07/18/1985
  • Status: Expired due to Fees
First Claim
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1. A pulse width discriminator circuit, comprising:

  • a D-type flip-flop having a data input, a clock input, a data output, and an inverted data output;

    a retriggerable monostable multivibrator having a trigger input, an external capacitance input, an external resistance-capacitance input, and an inverted data output;

    a capacitor; and

    first and second resistors;

    wherein said first resistor has one end connected to a source of power and its other end connected to said external resistance-capacitance input of said monostable multivibrator;

    wherein said capacitor has one end connected to said external capacitance input of said monostable multivibrator, and its other end connected to said external resistance-capacitance input of said monostable multivibrator, wherein said second resistor has one end connected to said data output of said flip-flop and its other end connected to said external resistance-capacitance input of said monostable multivibrator; and

    wherein when an input signal which is approximately a square wave is applied to said trigger input of said monostable multivibrator and to said data input of said flip-flop, said flip-flop produces at said inverted data output thereof an output signal which is a logic high voltage when the frequency of said input signal has exceede a fist predetermined frequency and until the frequency of said input signal thereafter falls below a second predetermined frequency which is less than said first predetermined frequency, and which is a logic low voltage when said input signal has fallen below said second predetermined frequency and until said input signal again exceeds said first predetermined frequency.

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