I would like to use one channel of a dual monostable (CD4538) to generate a pulse from either a rise or fall single trigger input feed. If I connect rise and fall trigger inputs together (or use a diode to ensure input B is always higher than input A with input signal fed to input B), will this produce an output pulse when triggered from either a rise or fall input?
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\$\begingroup\$ Have you thought about using a simulator? \$\endgroup\$– Andy akaCommented Dec 10, 2022 at 16:18
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\$\begingroup\$ It is probably about time I had a simulator, especially now that I am retired. I have a small drawer cabinet with components for umpteen projects. I also have an old prototyping breadboard that I shall use to experiment.. Thanks for responding. If anyone else wants an answer to this question, let me know and I will post experiment results. \$\endgroup\$– SPotterCommented Dec 11, 2022 at 12:04
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I would like to use one channel of a dual monostable (CD4538) to generate a pulse from either a rise or fall single trigger input feed.
I don't think your proposed circuit idea will work but, you can use an exclusive-or gate to produce a short pulse whenever the input signal changes state. This can then be used as it is (i.e. without a monostable) or used with a conventional monostable circuit. The ex-or circuit I'm talking about is called an "edge detector". This one uses an ex-or gate and two inverters: -
Images from here. Or, you can extend the pulse width using a Schmitt-trigger ex-or and an RC delay: -
By extending the RC time delay (and using a Schmitt-trigger ex-or) you can implement the monostable time delay i.e. make the pulse wider.
answered Dec 11, 2022 at 12:37