Re: The mechanism behind bouncing...

On Sat, 03 Feb 2007 21:58:27 +0000, Jon Slaughter wrote:
"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
On Sat, 03 Feb 2007 08:13:46 GMT, "Jon Slaughter"
"KILOWATT" <kilowatt"nospam"@softhome.net> wrote in message

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.

Well, you clearly have your head in the clouds. Contact bounce is what
happens when the contacts bounce. And physical stuff bounces when it
slams into other physical stuff. In a switch or relay you probably
want to move the contacts fairly quickly, and since we only have real
materials to work with, when contact "C" hits contact "A", it phycically,
mechanically, measurably, bounces, just like a tennis ball.

Try hitting an anvil with a hammer some time and see if you can make it
_NOT_ bounce! :-)

Good Luck!
Rich

.

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