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POLICE_SIREN_USES_FLASHER

2014-11-14 14:09  
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POLICE_SIREN_USES_FLASHER
Low-drain circuit operating from 1.5-V cell uses National LM3909 flasher ICs to simulate whooper sounds of electronic sirens used on some city police cars and ambulances. Two flashers are required for generating required rapidly rising and falling modulating voltage. Transistor is connected as diode to force ramp generator of IC to have longer ON periods than OFF periods, raising average tone and making modulation seem more even.-P. Lefferts, Power-Miser Flasher IC Has Many Novel Applications, EDN Magazine, March 20, 1976, p 59-66.