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Subject: Re: Momentary On/Off Switch Circuit

Date: 01/18/02 at 8:02 AM
Posted by: David Ashby
E-mail: dashby@quin.co.uk
Message Posted:

In Reply to: Momentary On/Off Switch Circuit posted by Joe Karp on 01/17/02 at 1:16 PM:

Hello Joe,

Your requirements break down into 2 funtions - first to filter out multiple transitions due to contact bounce when the switch is pressed and released, and second to provide the toggling of the LED state. I am not aware of a single device that is purposely designed to implement both these functions.

For debouncing, MAXIM do a range of small, surface mounted I.C.s: MAX6816, MAX6817, MAX6818 which can debounce 1, 2, or 8 switches respectively. The single-switch MAX6816 is probably the smallest solution, since it does not need external passive components to implement the contact bounce filtering function. The output from the MAX6816 will have to wired to the clock input of a flip-flop, which then provides the toggle function.

If you are desperate about using only I.C., I think it might be possible to fool a 4013 CMOS dual flip-flop into doing the job. You use one flip-flop as a schmitt trigger gate to debounce the switch - thats the tricky bit - and the other flip-flop to do the toggling. But as it will involve a few passive components, it would not be a smaller solution than using the MAXIM part. I could send you a sketch of the idea off-line if you wish - it would take too many words to describe here.

David Ashby.

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