Communications: electrical – Systems – Call station
Patent
1975-12-08
1978-04-04
Caldwell, Sr., John W.
Communications: electrical
Systems
Call station
250381, 340249, G08B 1710
Patent
active
040830373
ABSTRACT:
A battery-powered fire alarm including a smoke detector, a controllable horn circuit and a battery monitoring circuit. The smoke detector employs a pair of complementary field-effect transistor switches with gates respectively connected to an ionization chamber and a potentiometer of a Wheatstone bridge circuit connected across the battery. The field-effect transistors are biased off to minimize standby power consumption and are connected such that the threshold voltages thereof are offsetting to minimize supply voltage sensitivity of the detector. When the voltage from the ionization chamber assumes a value approximately equal to the potentiometer voltage, both field-effect transistors turn on to energize an alarm circuit to sound an alarm. The switching circuit is provided with hysteresis through positive feedback. The battery monitoring circuit employs a pair of complementary field-effect transistors connected with each other to establish a reference voltage to which the battery voltage is compared. The reference voltage is a function of both the threshold characteristics of the field-effect transistors and the magnitude of a preselected control voltage. Both field-effect transistors remain off until a low battery voltage condition is sensed to minimize standby power consumption.
REFERENCES:
patent: 3505663 (1970-04-01), Yule
patent: 3594751 (1971-07-01), Ogden et al.
patent: 3603811 (1971-09-01), Day et al.
patent: 3718919 (1973-02-01), Sasaki et al.
Caldwell Sr. John W.
Myer Daniel
Patent Development & Management Company
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