[sdiy] Debounce & hold +5v signal for 1/10 seconds

[Scott Gravenhorst]

"Andreas Gaunitz" <Andreas.Gaunitz at konstfack.se> wrote:
>
>Hi!
>
>Newbie disclaimer: I'm new to this list, as well as to electronics, =
>except for some simple mods to synths, phones etc.
>
>I'm trying to find out how to build a "One shot gate-signal generator", =
>trigged by a photo diode and a mechanical momentary swith. The length of =
>the gate signal is to be set by a pot, and should be in the "few tenths =
>of a second" range. Once the gate is on, it mustn't retrig until the =
>time has elapsed.
>
>I've found a lot of info (web etc) on debouncing, using passive filter =
>or RS latch. I have a hard time figuring how to set the hold time =
>though... Should I use a 555? It seems a little over complicated.
>
>Anyone have an idea or a schematic?

Welcome to the list, Andreas.

The app note I have for the 555 timer indicates that it is nonretriggerable
as a one shot, so this part would fit your needs.  I would suggest using
ICM7555 or equivalent CMOS version (much less rail noise).  I don't see
using a 555 as overcomplicated at all - what you describe is one of the
things it was designed for.  And they're CHEAP!  If you want
overcomplicated, you can always build the oneshot out of discrete parts...

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