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<TITLE>SV: [sdiy] Debounce & hold +5v signal for 1/10 seconds</TITLE>
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<P><FONT SIZE=2>"Andreas Gaunitz" <Andreas.Gaunitz@konstfack.se> wrote:<BR>
>><BR>
>>Hi!<BR>
>><BR>
>>Newbie disclaimer: I'm new to this list, as well as to electronics, =<BR>
>>except for some simple mods to synths, phones etc.<BR>
>><BR>
>>I'm trying to find out how to build a "One shot gate-signal generator", =<BR>
>>trigged by a photo diode and a mechanical momentary swith. The length of =<BR>
>>the gate signal is to be set by a pot, and should be in the "few tenths =<BR>
>>of a second" range. Once the gate is on, it mustn't retrig until the =<BR>
>>time has elapsed.<BR>
>><BR>
>>I've found a lot of info (web etc) on debouncing, using passive filter =<BR>
>>or RS latch. I have a hard time figuring how to set the hold time =<BR>
>>though... Should I use a 555? It seems a little over complicated.<BR>
>><BR>
>>Anyone have an idea or a schematic?<BR>
<BR>
<BR>
>Welcome to the list, Andreas.<BR>
<BR>
>The app note I have for the 555 timer indicates that it is nonretriggerable<BR>
>as a one shot, so this part would fit your needs. I would suggest using<BR>
>ICM7555 or equivalent CMOS version (much less rail noise). I don't see<BR>
>using a 555 as overcomplicated at all - what you describe is one of the<BR>
>things it was designed for. And they're CHEAP! If you want<BR>
>overcomplicated, you can always build the oneshot out of discrete parts...<BR>
<BR>
<BR>
Thank you!<BR>
<BR>
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!<BR>
<BR>
Now off to try and find a photo diode that is NOT sensitive to IR...<BR>
<BR>
Best regards, Andreas<BR>
<BR>
</FONT>
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