Re: The mechanism behind bouncing...

On Sat, 03 Feb 2007 21:58:27 GMT, "Jon Slaughter"
<Jon_Slaughter@xxxxxxxxxxx> wrote:


"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:kcl9s21bv0ulr6m2sdjlnkffdftp8mh68c@xxxxxxxxxx
On Sat, 03 Feb 2007 08:13:46 GMT, "Jon Slaughter"
<Jon_Slaughter@xxxxxxxxxxx> wrote:


"KILOWATT" <kilowatt"nospam"@softhome.net> wrote in message
news:45c3aa6d$0$31564$c3e8da3@xxxxxxxxxxxxxxxxxxxx
Hi... thanks for your attention.

I just wish to know the precise reason why for example, a digital
counter
may count many pulses on it's clock input when the clock is feed via a
non
noise-free source like a mechanical switch. It is because when the
contacts
makes/breaks, arcing (i've read somewhere that there can be a
possibility
of
arcing even at low voltage) occurs, or if it's because of the very rough
surface (microscopically-speaking) of the switch contacts, were the
metal
molecules grinds (and possibly flexes) together, during switch
activation?
TIA for your reply.



The atoms of the two materials are not configured in such a way that there
is complete contact. If they were then the materials would be fused. Since
there are not fused and they slide there is friction involved and this
friction causes the contacts to move farther a part and then closer
together. So the average distance between the constants is changing
significantly campared to when is not moving and they are making good
contact. So now the electric field is changing because of the distances
changing between the contacts. As the contacts move farther away the field
becomes weaker but now we have a capacitive effect. This effect creates a
force between the contacts that attract them. One now has a kinematic
force
pulling the contacts away(so it can slide), one of friction that wants to
stop the slide, and one of capacitance that is attractive(I'm sure there
are
more too).


Sorry, but that's all nonsense. At low voltages and currents, switch
contacts bounce for purely mechanical reasons.


Um, and you seem to think that mechanical bouncing is some real thing. Its
an abstract concept. There is no real think as bouncing. When a ball bounces
you think that the surfaces are idealized. No, they are governed by quantum
mechanics. Believe it or not, doesn't matter ot me.

If your field theories were true, the applied voltage would radically
change the bounce waveform. It doesn't. Try it.


hmm. so the waveforms are exactly the same? They do not scale with voltage?
You seem to think that ohms law doesn't apply here? V = IR or did you not
learn that? What do you really think these waveforms will look like? Do you
think they will be perfect unit step functions? Get into the real physics
of it and stop trying using idealized descriptions of the behavor.

http://www.ece.uci.edu/rfmems/publications/papers/mems/C021-EUMTT99.pdf

That paper describes a simulated mems switch that is electrostatically
operated and *never* makes electrical contact. That's not very
relevant to a conventional mechanical contact that is mechanically
driven and *does* make electrical contact.

Get an oscilloscope, a toggle switch, a power supply, and a resistor.
Set up to observe the bounce waveform. See if changing the applied
voltage changes the nature and timing of the bounce waveform, which is
must if electrostatic forces are significant. Of course the voltage
will change when you change the voltage; I won't argue that point.

This is real physics: try it.



http://www.scienceprog.com/dealing-with-switch-bounce-problem/


That says nothing about the physics. And it's actually easier to
"debounce" a pushbutton: just read it every 50 milliseconds and accept
what you see.


Your logic is like saying a resistor behaves exactly the same no matter what
conditions. Your a bafoon in thinking that everything is some simple
mathematical equation that you learned in cal 101.

No, I'm an engineer who knows how real parts actually behave.

Metallic conduction is not "arcing." Arcing is gaseous conduction.
Vacuum tunneling happens too, but the range is just on the order of an
atomic diameter, not important for things like switch contacts.



So we cannot have an arc in a vacuum without any gas? Hmm, can you prove
this? I think this would go to explaining a lot about vacuum tubes(I guess
they don't "arc" or must contain a gas(a significan't amount to explain the
arcing)).

Vacuum tubes don't arc in normal operation; thyratrons do. Arcing is
plasma (ionic) conduction. Vacuum tubes operate by electron-only flow.
Metals conduct through movement of conduction-band electrons.

John



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