PIR device

Details PIR device PIR device

1999-05-19

2001-12-04

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250SDIG001

Reexamination Certificate

active

06326622

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention is directed to a control circuit and method for converting an analog signal from a passive infrared (“PIR”) detector into a digital signal. More specifically, the device converts infrared detected by a passive infrared detector into a digital signal through the use of an oscillator.
SUMMARY OF THE INVENTION
The present invention is directed at a novel control circuit that may be used in lighting devices that use a PIR to sense “motion” in order to activate the lighting element of the unit. The present invention solves the problems associated with the control circuitry currently used in such devices by eliminating the use of PIRs in combination with comparators to detect “motion”. The present invention does this by coupling a PIR to a signal controlled oscillator that converts the analog signal generated by the PIR into a digital output that may be used by a microprocessor or other similar logic device. In current designs, PIRs are typically coupled to a number of comparators which are used to detect the presence of motion through changes in the infrared detected. However, there are several drawbacks to this type of design.
First, the use of comparators requires the use of additional components which increase the cost of the unit. Moreover, the use of comparators limits the unit's ability to supply useful and accurate information to a microprocessor or similar logic device. In addition, the comparators are affected by changes in environmental conditions such as changes in temperature, humidity and the like, which, in turn, create false readings. For example, at sub-zero temperatures, most prior art devices using comparators will cease functioning. In addition, if the environmental temperature exceeds that of the comparator's threshold level, the device will incorrectly sense motion and remain active until the environmental temperature falls within the preset thresholds.
The present invention solves the above mentioned shortcomings of the prior art designs by coupling PIR to an oscillator which produces a digital frequency that is inputted to a logic device. The logic device may employ variable threshold logic to sense changes in temperature as a function of time in order to detect motion. This differs significantly from prior art designs which use fixed thresholds to detect changes in temperature to detect “motion”. Consequently, eliminating the use of a fixed threshold improves the accuracy of the device since it eliminates inaccurate triggering or failure to trigger situations.


REFERENCES:
patent: 5077549 (1991-12-01), Hershkovitz et al.
patent: 58097680A (1983-06-01), None
patent: 06148341A (1994-05-01), None

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