BOUNCELESS_SQUARE_OUTPUT

Published:2009/6/29 2:39:00 Author:May | From:SeekIC

NE555 timer eliminates need for gates to suppress contact bounce. Timer can provide pulse at least 5 ms long (much longer if desired) and can remain on as long as trigger input (key pulse) is low (grounded). Timer triggers on negative-going edge of low-going pulse, such as key down to ground. Common negative is isolated from ground. VCC can be 5 to 15 VDC. Timer output can be connected directly to exciter keying input for negative grid keying. Because of square-wave output on make or break (100 ns each), circuits must be added in exciter or between keying transistors to provide at least 5-ms rise and fall times for Morse or RTTY key-ing.—B. Conklin, Improving Transmitter Keying, Ham Radio, June 1976, p 44-47.



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