Re: slightly off-topic: switch de-bouncing

There is also the old tried and true 555 monostable circuit that you could use.
Doing a quick search I come up with this page...

http://www.mitedu.freeserve.co.uk/Circuits/Switching/debounce.htm

If you want to only add one additional IC, I think a 556 is a dual 555

Anthony Ramos wrote:
>
> on 03 09 01 18.03, Marc Alexander at marc@wolfems.com.au wrote:
>
> >
> > There's something up with this, the LS02 is actually a NOR gate, and
> > the LS04 is an inverter. I guess the IC's are labeled backwards?
> >
> Sorry, the inverters are an LS04, and the gate is an AND (LS08).
>
> > You definitely want to change the inverter to an LS14, which is a
> > 'Schmitt trigger' input, it has hysteresis on the input.
> > Meaning that if the output is low, it will take eg. <1V to make it go high,
> > and if the output is high, it will take eg. >3V to make it go low.
> > This dead band gives excellent noise rejection as the input needs
> > to move eg. 2V for the output to change.
> > I've used 1V and 3V as examples, the data sheet for the IC has exact values.
> >
>
> Okay. I replaced the LS04 inverter with an LS14. The results are a little
> better, but not much different.
>
> > As Rodger said, 1uF or maybe more is good for the caps also.
>
> I'm about to replace the caps, but I don't know how to read the -)|- symbol.
> Which side of the cap should I tie to ground? The existing caps (.1µf) are
> not polarized.
>
> > The output isn't a 'pulse', it will stay low while both buttons are held down
> > together.
> > (is this the way it's supposed to work?)
>
> Yes, the output stays high while both buttons are pressed.
> I'm relying on the data book's statement that the counter only reads a
> rising edge. Right now, the counter pulses on button press *and* release. I
> think that's because of bounce. Hopefully, once the bounce is gone, the
> double triggering will be gone, too.
>
> corrected diagram:
>
> >>> +5v
> >>>
> >>> | |
> >>> \ \
> >>> / / 1K
> >>> \ \
> >>> / / LS14
> >>> | | 220 Ohm (Schmitt triggers) ____
> >>> Start 1 []------+-----/\/\/\/--+--------|>o-------| \
> >>> | | |LS08|-- output
> >>> Start 2 []---------+--/\/\/\/------+----|>o-------|___/
> >>> | | (AND)
> >>> - - 1µF
> >>> - -
> >>> | |
> >>> === ===
> >>> = =
> >>>
> --
> Anthony Ramos________
> 600 SE 39th Ave., # 3 \__ aramos@ele-mental.org .. aramos@hyperreal.org
> Portland, OR 97214 \___ information design .. multimedia production
> (503) 236-6303 \____________interactive art .. image synthesis
>
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-- 
later,
  jess
***** I have a new email address... jess@askey.org *****
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