Hi,
I need help to get a one-shot pulse generator with
both positive and negative trigger input. 555 timer
only takes negative trigger input. 74LS123 can take
either positive or negative but not both.
Thanks a lot for help!
Tom
Hi, Tom. I like the CMOS 4538. It has two one-shots on one 16-pin IC
Each has separate input pins for positive edge triggering and negative
edge triggering. Each also has a reset input, and positive and
inverted outputs. Output pulse widths extend from less than 100us to
over one second. Timing is set with one R and one C per one shot.
For pulses less than 100us, use the 4528, which has the same pinout.
Both operate on +3V to +15V supplies, like the 555. The only negative
is that the output is made to drive CMOS logic gate loads instead of
the high load a 555 can drive. However, by adding a transistor and two
resistors, you can make the 4538 drive as much or more current than a
555.
Also, the 4538 is set up to be retriggerable (another pulse will
restart the time). However, it's trivial to wire it up to be
non-retriggerable, like a 555.
http://www.onsemi.com/pub/Collateral/MC14538B-D.PDF
Good luck
Chris