Re: Minimum switch current

On Wed, 01 Aug 2007 16:59:21 +0100, Eeyore
<rabbitsfriendsandrelations@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.
Why am I not surprised?
---

My answer does at least point out that there are switches designed for this kind of
use. Tact switches would be a classic example. Gold plated contacts are not essential.
http://www.google.com/search?&q=tact+switch

---
All you've given an example of is low current hot switching, not dry
switching, and the switches you're referring to are designed to hot
switch low currents.

In some applications where hermetic sealing isn't an option and
greater reliability is needed than can be provided by base metal
contacts, gold or rhodium plated contacts may very well be
essential.


--
JF
.

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