| 摘要 |
1525974 Electrophonic sound producing devices REDIFFUSION REDITRONICS Ltd 10 Sept 1976 [16 Sept 1975] 38002/75 Heading G5J A twin tone automatic tone generator comprises control circuits (a monostable 1,2 and an inverter 4) which control OR gates 3 and 5, respectively, of an oscillator 3, 5, 6 to generate a burst of oscillations at a first frequency and a subsequent burst at a second frequency and also control an attenuator to increasingly. attenuate the level of the oscillations within each burst (dependant on the voltage across a capacitor 51). As described, the resultant square wave oscillations are filtered by a low pass filter 12 and gated 7, 8, 9 and 10 into a public address system.
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