Battery tach

  • US 5,004,979 A
  • Filed: 03/16/1990
  • Issued: 04/02/1991
  • Est. Priority Date: 11/03/1987
  • Status: Expired due to Term
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First Claim
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1. A circuit for providing an output signal representative of speed of an internal combustion engine of the type having an electrical ignition system connected to a battery, the circuit comprising:

  • means for deriving directly from the battery an input signal representative of time-varying components in battery current, where battery current is the current flow appearing at a battery terminal;

    means for filtering the input signal to produce a filtered signal comprising time-varying components of the input signal having frequencies within a range of frequencies associated with a time-varying signal impressed upon the battery current by operation of the ignition system; and

    means for suppressing components in the filtered signal not associated with ignition system operation to produce the output signal as a function of engine speed.

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