High-Volume Alarm

055 HIGH-VOLUME ALARM When this alarm is actuated by a low-level signal at input W, the (FiF) loudspeaker produces a number of 4-tone sequences sep- arated by quiet intervals. Each sequence sounds louder than the previous one to give the alarm a very distinctive character. The peak output is reached after about 28 seconds. As long as the N input is logic high, counters ICla and IC1b ELEKTOR ELECTRONICS JULY 1989 SUPPLEMENT remain reset and interval oscillator N2 and tone generator N3 are disabled. The alarm is then off. When Fr is actuated, the oscillator and the two counters are enabled. Counter ICla is clocked with pulses (PRF = 8 Hz) from N2. Gates N1 and N4 at counter outputs QO and Q3 cause T1 to be turned off during eight consecutive clock cycles from ICla. GENERAL INTEREST 36 During the next eight cycles, the transistor is alternately switched on and off as illustrated in the timing diagram. The loudspeaker sounds only when T1 conducts. Since output Q3 of counter ICla is ...