GAS_SMOKE_DETECTOR_WITH_LATCH

Published:2009/7/5 22:36:00 Author:May | From:SeekIC

CMOS latching logic provides 2-min time delay to prevent false alarm when power is first applied to fire alarm using Taguchi TGS308 gas sensor whose conductivity increases in presence of combustible gases. Normal voltage of 3 VRMS across R4 increases to about 20 V in presence of fire. Half of 12.6-V center-tapped transformer secondary is used for 6-V supply and full 12.6 V for DC horn supply. Latch is reset manually with S1 to turn off alarm after gas level drops. Optional circuit shown can be used for automatic reset.-A, Pshaenich, Solid State Gas/Smoke Detector Systems, Motorola, Phoenix, AZ, 1975, AN-735, p 5.



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