Use of ac to extend switch life.

Thread Starter

sternpirate

Joined Dec 10, 2015
25
As a hobbyist I was wondering about how to extend ultra sub miniature microswitch life, used in a usb mouse. I am well aware of different debouncing methods, what I am interested in is breakdown of the contacts. I read an article about how ac is better for switching purposes because it is self extinguishing of electrical arcs. So for instance could I build an ac oscillator to supply each switch and check for voltage at the microcontroller. what frequency would be best? the standing wave ratio would be terrible but I guess some circuits are resistant. what output devices should be used? any opinions?
 

dl324

Joined Mar 30, 2015
16,846
The switches in your mouse won't be subject to any meaningful electrical stress. Lifetime will be limited by the mechanical durability of the design. Aside from using the buttons as little as possible, there's little you can do to extend lifetime.
 

Thread Starter

sternpirate

Joined Dec 10, 2015
25
The switches in your mouse won't be subject to any meaningful electrical stress. Lifetime will be limited by the mechanical durability of the design. Aside from using the buttons as little as possible, there's little you can do to extend lifetime.
I read a post saying microswitches shouldn't see more than 20ma or lifetime will be shortened. I'm currently giving them 40ma (i think). what is the sweet spot for current? too little would be intermittent.
 

dl324

Joined Mar 30, 2015
16,846
I read a post saying microswitches shouldn't see more than 20ma or lifetime will be shortened.
Without some context, a statement like that is meaningless. I have some Cherry microswitches that are rated at 10A. They're larger than any that would ever be used in a mouse, but they're still considered microswitches.
I read a post saying microswitches shouldn't see more than 20ma or lifetime will be shortened. I'm currently giving them 40ma (i think).
Get the specs for the switches you're using and don't exceed the current rating. Switches from a mouse would have never been subjected to excessive current so using switches that far exceeded specs would be a waste of money.
 

Thread Starter

sternpirate

Joined Dec 10, 2015
25
thanks for responding. the context was in reference to mouse microswitches. I guess there is no way to know without testing a new switch until it self destructs.
 

spinnaker

Joined Oct 29, 2009
7,830
As a hobbyist I was wondering about how to extend ultra sub miniature microswitch life, used in a usb mouse. I am well aware of different debouncing methods, what I am interested in is breakdown of the contacts. I read an article about how ac is better for switching purposes because it is self extinguishing of electrical arcs. So for instance could I build an ac oscillator to supply each switch and check for voltage at the microcontroller. what frequency would be best? the standing wave ratio would be terrible but I guess some circuits are resistant. what output devices should be used? any opinions?
Where on earth did you read that there is arcing going on inside those tiny low voltage switches??? Maybe there is some but so tiny that it is nothing to worry about.

It isn't the current that is breaking down those low voltage, low current switches. It is the simple mechanical manipulation. Pick a properly sized good quality switch and be done with it. If you can find anything that suits your needs as far as life then look to a solid state solution like an optical switch.
 

Thread Starter

sternpirate

Joined Dec 10, 2015
25
Find the manufacturer part number and get the datasheet.

Or buy switches that you know meet your requirement.
10-4 good buddy
Where on earth did you read that there is arcing going on inside those tiny low voltage switches??? Maybe there is some but so tiny that it is nothing to worry about.

It isn't the current that is breaking down those low voltage, low current switches. It is the simple mechanical manipulation. Pick a properly sized good quality switch and be done with it. If you can find anything that suits your needs as far as life then look to a solid state solution like an optical switch.
well some of the switches I pulled apart had black carbon buildup. I can't change the switches as I am just modding an existing mouse shell.
 

spinnaker

Joined Oct 29, 2009
7,830
10-4 good buddy

well some of the switches I pulled apart had black carbon buildup. I can't change the switches as I am just modding an existing mouse shell.

Extremely doubtful that is carbon build up. More than likely just corrosion or dirt. Or you are putting abnormally high voltages through that switch.
 

Danko

Joined Nov 22, 2017
1,829
Without some context, a statement like that is meaningless. I have some Cherry microswitches that are rated at 10A. They're larger than any that would ever be used in a mouse, but they're still considered microswitches.
Microswitch named so because of very short (micro) changeover time, usually about 10 ms.
Moving parts of microswitch acsellerated by flat spring, which often lose strength or even becomes broken.
 

Audioguru

Joined Dec 20, 2007
11,248
Cheap switches have silver plated high current contacts where a spark cleans off the black silver oxide corrosion. They fail when used for low levels because silver corrodes. You should use high quality switches with gold plated contacts that are made for low levels and work well because gold does not corrode. The gold plating costs the same as a quality silver contact switch.
 

Thread Starter

sternpirate

Joined Dec 10, 2015
25
...or is the switch discharging a large capacitor as part of a debounce circuit?
no, it is just a run of the mill mouse circuit
Cheap switches have silver plated high current contacts where a spark cleans off the black silver oxide corrosion. They fail when used for low levels because silver corrodes. You should use high quality switches with gold plated contacts that are made for low levels and work well because gold does not corrode. The gold plating costs the same as a quality silver contact switch.
thanks, i'll look into it.
 

mcgyvr

Joined Oct 15, 2009
5,394
Cheap switches have silver plated high current contacts where a spark cleans off the black silver oxide corrosion. They fail when used for low levels because silver corrodes. You should use high quality switches with gold plated contacts that are made for low levels and work well because gold does not corrode. The gold plating costs the same as a quality silver contact switch.
Bingo..
In general with contact voltages of 12V/400mA or less gold plating is the preferred contact finish to reduce issues with oxidation/sulfate related failures..

Most platings also have a minimum arc voltage/current rating where no arc is formed.. (usually around the same 12v/400mA area)
That arc actually becomes useful to break through the oxidation..
 

ebeowulf17

Joined Aug 12, 2014
3,307
Contacts in all microswitches are self-cleaning because of their mechanical origin. Contacts shifted along each other when bouncing finished but pressure force on flat spring still increasing.
See: "Standard miniature switch with self-cleaning contacts"
http://switches-sensors.zf.com/asia-en/product/snap-action-microswitch-miniature-d3/
Contacts in SOME microswitches are self-cleaning, because different switches have different designs, and not all of them are designed to deliberately drag their contacts across each other laterally.
 

Lyonspride

Joined Jan 6, 2014
137
You say AC, but how does the switch see this AC if it has no reference to zero volts? You could supply a 2v sine wave sitting on a 5v DC level and the switch won't know any different. The theory you refer to doesn't really work at low voltages, it's a more "high voltage" thing, in all likelihood the issue you mention would be easily solved by dripping in some contact cleaner.

What tends to happen with these microswitches, is they get dirty, then the user presses harder and harder trying to get it to work and eventually breaks the switch.
 

Danko

Joined Nov 22, 2017
1,829
"Microswitch" - patented name and all of them have same patented principle of design. Differently designed switch may be big switch, miniature switch..., but not "Microswitch".

"A microswitch is also known as a miniature snap-action switch. The term microswitch is a trademarked one, but it is also commonly used to describe these devices. The switches are notable for being able to change states with minimal physical force"

Some about microswitch design: https://hackaday.com/2017/04/17/microswitches-past-the-tipping-point/
 

Danko

Joined Nov 22, 2017
1,829
What tends to happen with these microswitches, is they get dirty, then the user presses harder and harder trying to get it to work and eventually breaks the switch.
Spring lost off its strength because now for spring they use any different materials but beryllium bronze.
"One of the highest strength copper based alloys available on the market today is beryllium copper, also known as spring copper or beryllium bronze. The commercial grades of beryllium copper contain 0.4 to 2.0 percent beryllium. The small ratio of beryllium to copper creates a family of high copper alloys with strength as high as alloy steel."
 
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Reloadron

Joined Jan 15, 2015
7,501
I read a post saying microswitches shouldn't see more than 20ma or lifetime will be shortened. I'm currently giving them 40ma (i think). what is the sweet spot for current? too little would be intermittent.
Microswitch is a name we have come to associate with a type of snap action switches. Actually Microswitch Corporation is now a division of Honeywell. While the action of the switch is snap acting the method of actuation can be a button, lever, plunger and a host of other actuation methods. As another forum member mentioned among many manufacturers manufacturing this type switch Cherry Switch is one of them. I have a Cherry version, button actuated sitting here rated at 10 Amps 125/250 VAC. I haven't a clue why someone would make the statement that microswitches should not see more than 20 mA of current. As to a mouse button? I would think that to be more a tactile button switch and in that case yes, low current. Finally I agree with everyone else, as long as a switch is used correctly, within its rated current, it will mechanically fail likely before the contacts fail electrically.

Well Thank You Danko, started this post, had a neighbor visit, and over an hour later clicked to post. :)

Just My Take....
Ron
 
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