Re: Minimum switch current

On Aug 2, 11:17 am, John Fields <jfie...@xxxxxxxxxxxxxxxxxxxxx> wrote:
On Wed, 01 Aug 2007 18:12:13 -0700, bill.slo...@xxxxxxxx wrote:
On Aug 1, 9:30 pm, John Fields <jfie...@xxxxxxxxxxxxxxxxxxxxx> wrote:
On Wed, 01 Aug 2007 16:59:21 +0100, Eeyore

<rabbitsfriendsandrelati...@xxxxxxxxxxx> wrote:

John Fields wrote:

Eeyore wrote:
Robert Scott wrote:

I noticed that some switches are specified for a minimum current as well as a
maximum current. Someone once told me that this is because that minimum current
is needed to "burn away" oxides where the metals contact. Well, this is a
problem for me because I am designing a low-power device that will run on a coin
cell battery. The switch that I want to use is specified for 1 ma. minimum
current. But I want to use the internal microcontroller pull-up for this user
input switch. Are there some types of switches that have no minimum current?
How much trouble can I expect if I just ignore the spec? What about putting a
01 uF cap around the switch to produce a short burst of high current when the
switch is closed?

A capacitor is probably the worst idea ever.

What you're describing is usually called 'dry switching'.

---
Whether that's what it's usually called or not,

It's the term I'm familiar with. In a typical application you might be switching say
50uA as a control signal. That's dry enought for my liking.

---
As with many other terms you're "familiar" with, your interpretation
of the term is flawed. By definition, if the contacts are switched
and there's _any_ voltage present across them when they're open or
_any_ charge flowing through them when they're closed, then that's
called "hot switching".

"Dry switching" occurs when there is no voltage across or current
through the contacts and the action, one on the other, is strictly
mechanical.
---

it's wrong. Read my reply to Sloman's post in this thread.

I don't agree with your post.

---
Neither would you agree if I stated that black was black.

I, at least, would jump at the chance to congratulate you for getting
something right at last.

You do seem to have caught one of my (rare) misconceptions here, but
since your theory about the meaning of "dry" in this context is even
less plausible than mine you haven't exactly enhanced your own
reputation in the process.

---
Once again, I refer you to:

http://www.leachintl2.com/english/english2/vol6/properties/how4.htm

and, more particularly, to:

"Dry circuit loads: No current is switched. The contacts carry
current only after they are closed or before they are opened. The
currents may be high, as long as they are not switched. Since there
is no arcing, contact resistance is kept low by using gold plating
or gold alloy contacts."
---

Not that I'm not claiming that you are wrong all the time, but one
could probably get equally reliable advice by consulting a random
number generator. After all, a stopped clock is still right twice a
day.

---
Really?

http://www.grainger.com/Grainger/items/6NN63
---

Nice try. Ever seen one in real life?

Why am I not surprised?

That is easy to explain. An expert is someone who knows how little
they know. You don't know how little you know, and interpret
corrections as personal attacks, rather than educational episodes.
Thus one more correction becomes one more attack from someone whom -
you chose to believe - hates you, rather than one more misconception
erased from your personal data bank (which probably ought to be
transcribed and sent to some kind of museum of primitive engineering,
for exhibition with the stone axes and the electronic circuits built
around the NE555).

---
LOL, that from someone with an axe to grind who would rather spend
tens of dollars on a non-555 solution to a trivial problem perfectly
suited for a 555!
---

To a man with a hammer, everything looks like a nail.

You never learn, mores the pity. Obviously, you used to be able to
learn, but you seem to have started losing the capacity a few decades
ago and the process seems to have pretty much gone to completion.

---
LOL again, since I, at least, manage to stay fairly well abreast of
things and still function in the marketplace.

Find the right customers, and you can make a living casting
horoscopes. If you are sufficiently ill-informed you can even think
that casting horoscopes is doing something useful for the customer,
rather than defrauding them.

You, OTOH... Well, let's just leave it at that, shall we? No
reason to be unkind to the unemployed.

I suppose that I too could make a living selling obsolete technology
to the unsophisticated, but since I happen know something about
current developments in electronic technology I'd have to tell them
that they could do better elsewhere.

--
Bill Sloman, Nijmegen

.

Relevant Pages

  • Re: Minimum switch current
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  • Re: Wont go potty at home
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  • Re: Minimum switch current
    ... The switch that I want to use is specified for 1 ma. minimum ... Sorry, Bill, but by definition, "dry" contacts (as opposed to ... from mercury-wetted reed relays (which really don't need any wetting ...
    (sci.electronics.design)
  • Re: Minimum switch current
    ... The switch that I want to use is specified for 1 ma. minimum ... Sorry, Bill, but by definition, "dry" contacts (as opposed to ... from mercury-wetted reed relays (which really don't need any wetting ...
    (sci.electronics.design)