10_min_TIMER

Published:2009/7/13 1:35:00 Author:May | From:SeekIC

Uses SN74121 as actableMVBR generating pulses at 4-s intervals, U2 and U3 divide pulsetrain by 144 to give period of 576s U4 is then turned on, producing positive output pulse lasting 20 s that turns on Q1 for driving keyer, sidetone oscillator, lamp, or other signaling device as reminder for amateur radio operator to make 10-min station identification. R1 adjusts timing.-H. Seeger, Ten-Minute Timer, Ham Radio, Nov. 1976, p 66.



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