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Signalling apparatus

  • US 4,538,139 A
  • Filed: 04/30/1982
  • Issued: 08/27/1985
  • Est. Priority Date: 04/30/1982
  • Status: Expired due to Term
First Claim
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1. Apparatus for signalling remotely a sensed change in a local condition;

  • said apparatus comprising;

    a base;

    a flat metal spring cantilevered from said base;

    bonded to a face of said spring, a piezoelectric film of polyvinylfluoride;

    means response to the sensed change in condition for snapping the free end of said spring causing the spring to oscillate at its resonant frequency, thereby causing said film to generate a pulsating voltage;

    means for rectifying and partially filtering said pulsating voltage thereby to provide a supply voltage having substantial ripple content at a frequency which is twice the characteristic resonant frequency of said spring frequency;

    a crystal frequency controlled r.f. transmitter interconnected with said film and powered by said supply voltage to radiate an r.f. signal modulated at a signalling frequency which is essentially twice the characteristic resonant frequency of said spring;

    a receiver for detecting and demodulating said radiated r.f. signal;

    frequency selective means responsive to the demodulated signal for detecting and responding to a detected frequency component within the demodulated signal at essentially twice the resonant frequency of said spring and for generating an output signal in response thereto.

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