Self-contained, condition responsive circuit

Details Self-contained, condition responsive circuit Self-contained, condition responsive circuit

1974-06-24

1976-01-13

Swann, III, Glen R.

Communications: electrical

Systems

Call station

340285, G08B 1706

Patent

active

039328490

ABSTRACT:
A self-contained, temperature responsive alarm control circuit uses a battery as an energy source. A solid state, free-running multivibrator provides a square wave of audio frequency which provides the pulse to turn on an emitter follower also at an audio frequency so as to energize a Wheatstone bridge across the battery at the same audio frequency. One of the legs of the Wheatstone bridge includes a temperature sensitive thermistor. A programmable unijunction transistor serves as a threshold detector for the bridge circuit which, upon its being gated into conditon upon the reaching of a predetermined, preset temperature sensed by the thermistor, provides a signal to turn on an audio amplifier at the same audio frequency thereby to energize a speaker now essentially coupled across the battery to produce an audible sound.

REFERENCES:
patent: 3191048 (1965-06-01), Cowen
patent: 3226705 (1965-12-01), Kaufman et al.
patent: 3680068 (1972-07-01), Hanchett
patent: 3778798 (1973-12-01), Heit
patent: 3815113 (1974-06-01), Welch

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