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

[Andreas Gaunitz]

"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...


Thank you! 

I've been browsing some more since I posted, and I found an extremely simple example circuit using the 555 that I'm sure will cut it!

Now off to try and find a photo diode that is NOT sensitive to IR...

Best regards, Andreas

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