KEYER_OSCILLATOR

Published:2009/7/11 3:24:00 Author:May | From:SeekIC

Oscillator or clock starts when key is closed and can be held until dot, dash, or space is completed. U1 is SN7400, and U2 is SN74L04. Diodes at input of U2A form OR gate that controls oscillator. These inputs can be used to keep oscillator running for self-completing action. Time constant, set by C1 and R1, is 4 ms which is width of clock pulse. Values for C2, R2, and R3 give pulse repetition rate of 50 to 95 ms, comesponding to about 12 to 24 WPM.For higher speeds, reduce values of C2 and R2.CR1 and CR2 are signal diodes that prevent first pulse from being different; 250-pF capacitor on output prevents noise spikes from triggering keyer circuits falsely.-J. T. Miller, Integrated-Circuit Oscillator, Ham Radio, Feb. 1978, p 77.



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