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Time-keeping apparatus

  • US 4,905,187 A
  • Filed: 05/20/1988
  • Issued: 02/27/1990
  • Est. Priority Date: 01/31/1986
  • Status: Expired due to Fees
First Claim
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1. Apparatus for keeping the time of day, comprising:

  • an input for receiving an AC power line voltage subject to interruption;

    processor means, including a source of clock signals, and a memory for storing a program of operating instructions;

    said processor means operating in a normal mode while said AC power line voltage is present to keep the time of day by counting cycles of said AC power line voltage; and

    an R-C network input for producing a varying voltage when triggered;

    said processor means operating to determine the duration of said interruption of said AC power line voltage so that the time of day can be updated by repetitively triggering said R-C network to produce repetitive cycles of said varying voltage during said power interruption, said cycles each consisting essentially of a voltage ramp from a first predetermined voltage level to a second predetermined voltage level and having the same substantially constant duration; and

    calculating the time duration of said power interruption by measuring said substantially constant duration of said cycles and multiplying said substantially constant duration of said cycles by the number of cycles occurring during said power interruption.

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