Re: Looking for a circuit to

From: Terry Pinnell (terrypinDELETE_at_THESEdial.pipex.com)
Date: 07/08/04 

Date: Thu, 08 Jul 2004 07:40:28 +0100

"Robert C Monsen" <rcsurname@comcast.net> wrote:

>> OK, then my 555 model must be unrealistic, or my
>> schematic/configuration flawed. I still got spurious triggering when
>I
>> simulated it:
>> http://www.terrypin.dial.pipex.com/Images/WindowSwTimerSIM2.gif
>>
>> (If you want, I'll send you the CKT and PWL.)

>No, you put the diode to 5V on the wrong side of the 100k resistor.
>
>The problem is that the diode keeps that node from getting up above
>5.7V, so
>the quick drops of the far left side on switch bounce cause the chip
>to trigger.
>Putting the diode on the other side of the 100k resistor means it
>doesn't
>affect that node as much, which can now go up to 10V when the switch
>opens.
>Thus, bounces on switch open now bounce between 10V and 5V rather than
>5V
>and 0V, and therefore don't trigger the 555. The diode simply protects
>the
>555 from any damage that the 10V might cause, and is probably not
>required
>for cmos 555s, since they have input protection diodes anyway.

Thanks for the fast reply. Still simulates a retrigger! Can you see
any other error in this schematic?
http://www.terrypin.dial.pipex.com/Images/WindowSwTimerSIM3.gif

If not, has to be the model. Did you simulate as well as build it? 

-- 
Terry Pinnell
Hobbyist, West Sussex, UK