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After many search, I don't know still that what is exactly the difference between 4-leg and 2-leg momentary tactile switch?

4-leg:

4-leg

4-leg

2-leg:

2-leg

2-leg

Why do they use 4-leg in many cases? for example, in mobile phones, in many cases, they use 4-leg. look:

enter image description here

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marked as duplicate by Spehro Pefhany, RedGrittyBrick, Vladimir Cravero, Majenko, placeholder Jun 28 at 16:48

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

1  
@SpehroPefhany I don't know why haven't I seen that question so far! Thanks. –  Roh Jun 28 at 12:37
2  
There's more than one name for that kind of switch, probably that's why. Tact switch, momentary pushbutton, tactile switch, PCB-mount pushbutton, etc. –  Spehro Pefhany Jun 28 at 12:58
    
The 2 Legged switches are Breadboard friendly, 4 legged one's are PCB friendly. The 4 legged one's are a nightmare for breadboard'ing. –  vvy Jun 28 at 18:46
    
@vvy If you have to, you can insert the 4 legged switch into a breadboard if first you straighten its legs into the right orientation with pliers. But then you'll ruin it for anything else. –  Ricardo Jun 28 at 20:43

2 Answers 2

up vote 5 down vote accepted

Most people seem to think that the 4-leg tactile switches are made that way only to add mechanical strength, but Spehro Pefhany told us in this great answer that there is another, more important reason for the 4 terminals:

The dual shorted pins allow inexpensive single-sided boards to be used for X-Y matrices of switches without requiring jumpers.

In other words, the additional shorted terminals are meant to be used as jumpers.

X-Y matrices of switches

I have built one myself (see below). Those boards are a lot of fun to route.

Remote control schematics

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1  
Great!!! Thank you. –  Roh Jun 28 at 12:40

I've only ever used the 4-leg variety. My first impression is that they have more mechanical strength in how they mount to the PCB. The 4-leg parts also have legs that are bent so that they stay in the holes before soldering. You can flip the board upside down without the switch falling out.

The picture of the 2-leg part seems to show it is a old style thru hole, which is more difficult to work with. You can't flip the board over after insertion and before soldering, and then you have to clip the leads on the bottom. That all adds steps and cost. This is probably why the 2-leg parts are rare compared to the 4-leg parts. Check price and availability at a few mainstream distributors, and you'll probably find the 2-leg versions are a bad idea.

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+1 for nice question. also I have already checked it out for price. in terms of price, the both are equal. –  Roh Jun 28 at 11:38
    
Also I think there are another properties because for SMD type, they are almost equal. –  Roh Jun 28 at 11:41
1  
Roh, you're right, there is another reason. The additional shorted terminals are meant to be used as jumpers. See my answer for more details. –  Ricardo Jun 28 at 12:20
    
@Ricardo Thanks Ricardo –  Roh Jun 28 at 12:37

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