Wetted switch contacts

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Hi all,

 

I tried an experiment today which was completely successful and the info may be of use to some.

 

I have a small quantity of GALINSTAN which is an eutectic alloy of gallium, indium and tin (hence the name GAL(lium), IN(dium), STAN(num). Galinstan freezes at -19 degrees C, so it's liquid metal at normal room temperatures. Nice thing about it is that it's non-toxic.

 

The point of this post..... I connected an ordinary snap-action microswitch to 5 volts through a 1000 ohm resistor and connected it to my silly-scope to look at the contact bounce. Of course I had bounce galore!

 

Then I "tinned" the microswitch contacts with some Galinstan. Not even a drop, just enough to "wet" the contacts and make them shiny.

 

I reassembled the microswitch and tested the performance again. Absolutely ZERO bounce!

 

Looking at the contacts with a digital camera set to 8X speed, I looked at the contacts as they opened and closed. Upon closing, they just come together. Upon opening, there is a microscopic "string" of Galinstan which forms between the contacts. The string is only a fraction of a millimeter long and VERY thin. As the contacts come apart, the little string breaks and gets "sucked back" onto each contact (if all this makes any sense)?

 

Attached are scope screenshots of the switch performance.

 

(click thumb for full size)

JPEG Image

 

So, if anyone needs to make a switch that has zero bounce (and probably is more reliable due to the constantly reforming liquid metal contacts), get yourself a gram or so of Galinstan and try wetting your switch contacts!

 

I bought mine from a place called "RotoMetals", but it can be found other places (as well as home made - just get a bit of gallium and indium - you really don't need the tin) and just melt the two with boiling water and mix the proper ratio.

 

Be careful with it, it's SUPER messy. The tiniest drop will stain everything a gray-black (especially skin - it's not toxic but it's MESSY!). And, if you wear a wedding ring or any other gold - be sure to remove it before handling Galinstan. It will "tin" gold and it's impossible to remove it from the gold without using an acid to dissolve it. Be sure to wear no gold during handling the stuff, and wash your hands afterwards to avoid transferring any Galinstan to the gold.

 

Good luck!

 

 

Gentlemen may prefer Blondes, but Real Men prefer Redheads!

Last Edited: Tue. Mar 10, 2020 - 11:54 PM
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Krupski

 

There's commercial pen track.

 

-----------------------------------

When the pen track empty maybe will fill with GALISTAN(sounds like country/province to me)

 

Regards

JSB

.

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Krupski wrote:

So, if anyone needs to make a switch that has zero bounce (and probably is more reliable due to the constantly reforming liquid metal contacts), get yourself a gram or so of Galinstan and try wetting your switch contacts!

https://en.wikipedia.org/wiki/Galinstan

Galinstan may be used as a thermal interface for computer hardware cooling solutions, though major obstacles for widespread use are its cost and aggressive corrosive properties (it corrodes many other metals such as aluminium by dissolving them).

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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joeymorin wrote:

Krupski wrote:

So, if anyone needs to make a switch that has zero bounce (and probably is more reliable due to the constantly reforming liquid metal contacts), get yourself a gram or so of Galinstan and try wetting your switch contacts!

https://en.wikipedia.org/wiki/Galinstan

Galinstan may be used as a thermal interface for computer hardware cooling solutions, though major obstacles for widespread use are its cost and aggressive corrosive properties (it corrodes many other metals such as aluminium by dissolving them).

 

Does not sound very "Non-toxic" to me if it can do all that........YMMV

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

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Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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joeymorin wrote:

Galinstan may be used as a thermal interface for computer hardware cooling solutions, though major obstacles for widespread use are its cost and aggressive corrosive properties (it corrodes many other metals such as aluminium by dissolving them).

 

So can we then say that this is a hoax, and will only kill your switch after limited use?

 

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The snap dome in most tact switches is, I believe, a lightly tempered steel, but the top plate which caps the plastic housing and contains all of the bits is often aluminium. It's not clear either whether steel is susceptible, nor if the switch contacts and terminals, whatever they're made of, would themselves be susceptible.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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Krupski wrote:

So, if anyone needs to make a switch that has zero bounce (and probably is more reliable due to the constantly reforming liquid metal contacts), get yourself a gram or so of Galinstan and try wetting your switch contacts!

I bought mine from a place called "RotoMetals", but it can be found other places (as well as home made - just get a bit of gallium and indium - you really don't need the tin) and just melt the two with boiling water and mix the proper ratio.

Be careful with it, it's SUPER messy. The tiniest drop will stain everything a gray-black (especially skin - it's not toxic but it's MESSY!). And, if you wear a wedding ring or any other gold - be sure to remove it before handling Galinstan. It will "tin" gold and it's impossible to remove it from the gold without using an acid to dissolve it. Be sure to wear no gold during handling the stuff, and wash your hands afterwards to avoid transferring any Galinstan to the gold.

 

Or one could simply not open up a perfectly crappy switch and simply write a debounce routine in their code instead?

 

Seems like an awful lot of work for a switch that will now be compromised and may need replacing later.

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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I'd opt for software debounce any day.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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What happened to good ol’ mercury? Anything that works well is toxic - that’s why it works well! Just look at tetra ethyl lead, freon, asbestos. The list goes on.

Seriously though, every external input needs filtering - whether it bounces or not.

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Kartman wrote:
What happened to good ol’ mercury? Anything that works well is toxic

Your left out Round-up, and 24-D!  smiley

 

Jim

 

 

 

 

 

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Jeckson wrote:

Krupski

 

There's commercial pen track.

 

-----------------------------------

When the pen track empty maybe will fill with GALISTAN(sounds like country/province to me)

 

Regards

JSB

 

What does that mean "There's commercial pen track."?

 

Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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Jeckson uses a suspect translation service that seems to emit random english words that make sense to us.

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jgmdesign wrote:

joeymorin wrote:

Krupski wrote:

So, if anyone needs to make a switch that has zero bounce (and probably is more reliable due to the constantly reforming liquid metal contacts), get yourself a gram or so of Galinstan and try wetting your switch contacts!

https://en.wikipedia.org/wiki/Galinstan

Galinstan may be used as a thermal interface for computer hardware cooling solutions, though major obstacles for widespread use are its cost and aggressive corrosive properties (it corrodes many other metals such as aluminium by dissolving them).

 

Does not sound very "Non-toxic" to me if it can do all that........YMMV

 

Jim

 

Gallium will dissolve aluminum and indeed air transport of Gallium is prohibited. If some spilled onto an aircraft aluminum structure.....

 

Gallium is not toxic (unless you are a droid with an aluminum body).

 

The word "corrosive" is scary sounding and really is the wrong word to use. It REACTS with aluminum, not CORRODES aluminum.

 

It's like the word "radiation". I'm being bombarded by electromagnetic radiation right now. My room lamp emits radiation all over the visible spectrum, including invisible infrared. I'm also bombarded by EM radiation from the wireless router, 60 Hz from the power lines, microwaves from countless sources. Am I going to die of "radiation"? Certainly not.

 

Another misused word is "volatile". Most people think "volatile" means flammable, explosive, touchy, dangerous, etc... when in fact "volatile" means "it evaporates". Water is volatile, yet nobody is worried that a barrel of water will explode or burn.

 

Anyway, back on track. Gallium/Indium alloy is frequently used as a superior thermal interface material (like between a heatsink and a CPU). Gallinstan nicely wets the top of a metal cover CPU suck as an Intel CORE type, and it wets the copper core of a CPU heatsink/fan assembly. Together, you get a complete air-free metal interface between the heat sink and fan which as far superior to any "thermal compound" such as that silver filled silicone grease people use.

 

NASA used to make TO-3 package shaped Indium foils and use them to bond a transistor to a heatsink. They installed the transistor with spring loaded screws and heated the assembly until the Indium melted. Indium does not react with aluminum, so it was OK for aluminum heatsinks.

 

Only things to worry wbout: First, since Galinstan is a conductive metal, it cannot be allowed to exit the heatsink/CPU plane and drip on the PC board (this happens when TOO MUCH is applied). Second, only use it with a copper core heatsink. It will ruin an aluminum heatsink.

 

 

Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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meslomp wrote:

joeymorin wrote:

Galinstan may be used as a thermal interface for computer hardware cooling solutions, though major obstacles for widespread use are its cost and aggressive corrosive properties (it corrodes many other metals such as aluminium by dissolving them).

 

So can we then say that this is a hoax, and will only kill your switch after limited use?

 

 

It's not a hoax. And, the switch contacts are made of beryllium copper spring with silver plated contacts. Neither is hurt by Gallium.

 

I do agree, though, that a simple software debounce is simpler and more practical than taking a switch apart and tinning the contacts with Galinstan.

 

The point of my post was to report the results of an experiment I did, not to try to convert the world from using software debounce to wetted contacts!  laugh

 

 

 

 

Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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ki0bk wrote:

Kartman wrote:
What happened to good ol’ mercury? Anything that works well is toxic

Your left out Round-up, and 24-D!  smiley

 

Jim

 

 

You forgot Chlordane and Agent Orange!  smiley

 

Gentlemen may prefer Blondes, but Real Men prefer Redheads!

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Krupski wrote:

The word "corrosive" is scary sounding and really is the wrong word to use. It REACTS with aluminum, not CORRODES aluminum.

 

I strongly suspect the actual chemical reaction is that it reacts with AL2O3, aka aluminum oxide, which is the protective layer that protects mostly pure AL from O2.  Keep removing the oxide layer, and the atmosphere will burn* your aluminum.  That particular reaction will run until your AL metal has all rusted** away - not good for structural abilities. 

 

Without a protective oxide layer, AL will corrode** just fine by itself in an oxygenated atmosphere.

 

And I'll let you know when I feel like taking apart my microswitches and dolloping something poorly tested in there.  Send your sales pitch to Omron or Panasonic.  S.

 

* Technically, "Oxidation".  Done fast enough, we call that a 'fire'.

** Also technically "Oxidation".  Done slowly to iron and steel, we call that 'rust'.

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Krupski wrote:
What does that mean "There's commercial pen track."?

 

like at attachment\picture

 

 

regards

JSB

 

PS:When empty(pen track) then fill with Galistan will okPen track

.

Last Edited: Wed. Mar 11, 2020 - 06:33 AM
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Application Note 31 - Relays and Switches (Stabilant)

[mid-page]

Is Stabilant 22 just another contact cleaner?

No, Stabilant 22 is a resident potentially electrically active material which through a synergistic combination of effects enhances conductivity within a contact without causing leakage between adjacent contacts.

...

"Dare to be naïve." - Buckminster Fuller