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help pushbutton switch but I don't know its connections
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help pushbutton switch but I don't know its connections

by josheeg on Thu Nov 18, 2010 12:08 pm

help pushbutton switch but I don't know its connections what pin is a and connects to b? there are 4 and it is momentary so does that just mean they all connect?
I haven't bought it I am making the board now.
here is the mouser or manufactuer part number
KMS221G LFS
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Re: help pushbutton switch but I don't know its connections

by franklin97355 on Thu Nov 18, 2010 12:27 pm

If you haven't bought the parts you should not be making the board. That comes AFTER the parts are procured.

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Re: help pushbutton switch but I don't know its connections

by josheeg on Thu Nov 18, 2010 12:42 pm

why would I purchase a bunch of switches and things and not have the board layout done?

So your saying the data sheets are not trustworthly?

I am a little confused by what you mean by that but I am not very experianced.
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Re: help pushbutton switch but I don't know its connections

by mtbf0 on Thu Nov 18, 2010 1:16 pm

the datasheet is linked from the mouser page.
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Re: help pushbutton switch but I don't know its connections

by josheeg on Thu Nov 18, 2010 2:29 pm

I looked at the data sheet and I am surprised not to see it in there.
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Re: help pushbutton switch but I don't know its connections

by zener on Thu Nov 18, 2010 2:39 pm

Look carefully at the drawing. How many terminals does it have? Not how many pads are on the board, but how many terminals come out of the switch body? There is the answer.

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Re: help pushbutton switch but I don't know its connections

by josheeg on Thu Nov 18, 2010 3:03 pm

4 if it had 2 feet and two terminals that would make sence there are 4.
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Re: help pushbutton switch but I don't know its connections

by stinkbutt on Thu Nov 18, 2010 3:42 pm

If it has four pads then there are several ways it can be connected.

1. All four pads are unconnected normally and when the button is pushed all four connect.
Code: Select all | TOGGLE FULL SIZE
normal      pushed
o- -o         o---o
              |   |
o- -o         o---o


2. All four pads are unconnected normally and when the button is pushed two pairs of them connect.
Code: Select all | TOGGLE FULL SIZE
normal      pushed
o- -o         o---o

o- -o         o---o


3. Two pairs of pads are connected normally and when the button is pushed all four connect.
Code: Select all | TOGGLE FULL SIZE
normal      pushed
o---o         o---o
              |   |
o---o         o---o

I can't really tell from the datasheet which one it is. If I had to guess I'd say #3. But that's a 100% brown guess. If you get a hold of one you can just test connectivity to get your answer.
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Re: help pushbutton switch but I don't know its connections

by uoip on Thu Nov 18, 2010 4:32 pm

The data sheet says the contact arrangement is "SPST, N.O.". Of the three options stinkbutt presents, only the last one is SPST. The 2nd one is DPST and the first one is something I've never seen, but not SPST.

It's probably a variation on #3, but there are other possible ways a SPST switch could be arranged. I don't see it on the data sheet (shame on them for not making it explicitly clear there), but that's something that would be trivial to check in a second with a meter if you had the switch in hand.
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Re: help pushbutton switch but I don't know its connections

by uoip on Thu Nov 18, 2010 4:39 pm

OK, I found it. On page B-14 of the data sheet, on the engineering drawings, the final illustration on the top row. Overlayed on the drawing is a schematic. Translated to ascii, it looks a little like this.

--------
\
--------

That "\" character is a switch symbol (it's a lot clearer if you look at the data sheet instead of my ascii drawing).

So the horizontal pairs of pads are always electrically connected to each other. When the button is pushed, the top pair is connected to the bottom pair.
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Re: help pushbutton switch but I don't know its connections

by stinkbutt on Thu Nov 18, 2010 5:04 pm

Well I don't think the datasheet's a hell of a lot clearer. It's like the answer was hidden away in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying 'Beware of the Leopard.'

So it's case #3. Here's a big fat expanded version of the illustration.

spst2.png
spst2.png (41.34 KiB) Viewed 1866 times
Red M&M, Blue M&M: They all wind up the same color

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Re: help pushbutton switch but I don't know its connections

by zener on Thu Nov 18, 2010 5:31 pm

I stand corrected!

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Re: help pushbutton switch but I don't know its connections

by stinkbutt on Fri Nov 19, 2010 1:51 am

Zener wrote:I stand corrected!


Beware of the Leopard.
Red M&M, Blue M&M: They all wind up the same color

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