GB1180444A - Multiple Alarm System - Google Patents

Abstract

1,180,444. Transistor oscillator circuits. GENERAL ALARM CORP. 27 Feb., 1967 [1 March, 1966], No. 9167/67. Heading H3T. [Also in Division G4] An acoustic alarm comprises a tone generator 33 the frequency of which is modulated by a control generator 30 and has provision for changing the frequency and/or waveform of the output of the control generator 30 so as to produce alarm signals of distinctly different character. The circuit shown may be mounted on the inside of a door (Fig. 1, not shown) which may carry a bell push 26, a locking chain 22 and a temperature-responsive bi-metallic element 28. The operation of each of these devices results in a different tone being emitted by the loud-speaker 94. Electronic siren alarm.-Excessive tension on the locking chain 22 closes switch 42 which enables transistors 68, 70 to operate as a multivibrator the frequency of which is swept in sawtooth manner at 1 c/s. between 1200 and 1800 c/s. under control of a sawtooth oscillator 30 comprising a unijunction transistor 44. Electronic horn alarm.-Flexing of the bimetallic elements 28 due to excessive temperature closes contacts 42 and 86 and sets contacts 60 to their upper positions. Contacts 60 introduce variable resistor 64 in the frequency control line of the multivibrator 33 which has the effect of reducing the frequency of the multivibrator and increasing the frequency of the control generator 30 such that the output signal is swept between 400 and 600 c/s. at 30 c/s. Closure of contacts 86 alters the duty cycle of the multivibrator so that the sound is that of a deep-throated horn. Electronic bell alarm.-When the door bell button 26 is depressed, contacts 42 are closed and contacts 54 and 60 are set to their upper positions. Contacts 54 switch the output from the control generator 30 from a sawtooth to a pulse waveform which shock-excites the multivibrator repetitively into oscillation at two different frequencies giving a bell-like sound in the loud-speaker 94. Modification.-Fig. 3 (not shown), depicts a cross-coupled pair of complementary transistors which may replace the unijunction transistor 44.