DIGITAL_ALARM

Published:2009/7/1 2:16:00 Author:May | From:SeekIC

Direct drive offered by Fairchild 3817 IC allows design of simple Iow-cost clock radio providing display drive, alarm, and sleep-to-music features in 12- or 24-h formats.Display is Fairchild FND500 LED. Either 50- or 60-Hz input may be used. U2 is 7800-series IC volt-age regulator rated to meet requirements of radio used. Q3 provides active low output for timed radio turnoff after user-selected interval of up to 59 min. CR4 and C5 rectify alarm-tone output for amplification by Q4 to give active low output for timed radio turn-on when coincidence is detected by alarm comparators. Q5 provides alarm-tone output at level sufficient to drive 40-ohm loudspeaker with ample wake-up volume. If radio is used, omit loudspeaker. Article covers construction and adjustment.-D.Ft. Schmieskors, Jr., Low-Cost Digital Clock, Ham Radio, Feb. 1976,p 26-30.



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