Importance

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Abstract

A security system having one or more sending units for transmitting a digitized r-f signal representative of a condition such as fire, smoke, intrusion, battery condition, an emergency, or other condition to a central receiving unit. The sending units include a microcomputer which Manchester encodes the data. The receiving unit includes a microprocessor which samples the data signal 24 times per data bit. The moving average of the 12 most current samples is calculated and differentiated into a high or low value depending on the value of the previously calculated averaged value. The time between data transitions (from high to low or low to high) is evaluated and then stored as being a long (1) or a short (0) time since the previous transition. When all the data has been received, the stored values for length of time between transitions are checked for conformance to the transition timing requirements of Manchester encoded signals. Signals without the proper timing are discarded. Signals that conform to the proper timing requirements and which contain a valid cyclic redundancy code and transmitter identification code are gated to an output device to provide an indication of the condition.

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First Claim