[sdiy] Minimum parts count switch de-bouncer.

[Tim Parkhurst]

On 4/12/06, Dave Kendall <davekendall at ntlworld.com> wrote:
> Hi guys.
>
> Very grateful for all the help - going to have to decide now...... :-)
>
> Looks like the simplest, lowest parts count circuit, using stuff I've
> already got, is this circuit;
>
>                I-------------------------I>o------------o out
>                I                     schmitt trigger
> +15V            I
>    I     sw    I   I------I Rx I-------I
>    I    ____   I   I                   I
>    I----o  o-------I                   I
>                    I      +            I
>                    I------II Cx II-----I----GND
>
> <snip>
> </snip>
> where Rx = 10k, and Cx = typically 1uF. I'm not sure, but from what I
> understand, the pulse duration in ms is R in Kohms, x C in uF = 10ms.
> Am not sure if the output pulse will be negative or positive going.
>
> I guess the +15V and GND connections could be reversed (making sure the
> electro is reversed too) to change this?
>
> I'm soldering away right now, so we'll see soon...
>
> cheers,
>
> Dave
>
*********************
Hi Dave,

I would say that you're on the right track, but the solution you have
above will produce a signal that goes from +V to GND when the switch
is pressed (assuming that the schmitt trigger is a 40106, which is an
inverter). I don't remember the original application, but if that's
what you need then you're ready to go. Otherwise, if you need a
positive going signal when the switch is pressed, just connect the R
and C to +V and make the switch connect to GND when it is pressed. Oh,
and reverse the electrolytic. Speaking of which, you don't really need
an electrolytic cap in there. You can easily get away with a cheap
ceramic disc cap for this.

Tim (cheap but not ceramic) Servo
--
"Imagination is more important than knowledge." - Albert Einstein