TWO_TONE_ALARM

Published:2009/7/6 21:07:00 Author:May | From:SeekIC

Provides audible backup for visual display in microprocessor-controlled system that requires human intervention under certain conditions, to alert operator who may be watching machinery rather than display. When input line goes high, device emits 1-s beep that means stop. When input goes low, 1-s lower-frequency boop sounds to indicate go. S1 represents signal derived from single-bit computer output. Audio bursts are generated by 555 timers, IC2 is wired as mono MVBR to determine tone duration, set by C4 and R11.Negative-going pulse on pin 2 triggers mono on. ff microprocessor circuit creates pulse rather than level change, input should go to pin 2. Tone frequency is set by C5, R13, and R14 of IC3. Trigger uses IC1A as inverting opamp and IC1B as noninverting opamp. Trigger outputs are differentiated to give negative-going spike for each input level change. Spikes are ORed by Dl and D2 for trigger input of IC2. Different tones are achieved by using IC1A to change input voltage to pin 5 of tone generator IC3. 0p-tional electrolytic capacitor across R24 will in-crease volume.-C. F. Douds, Audible Interrupts for Humans, BYTE, Feb. 1977, p 54 and 58.



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