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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

Roh
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    @SpehroPefhany I don't know why haven't I seen that question so far! Thanks. – Roh Jun 28 '14 at 12:37
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    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 '14 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. – vyi Jun 28 '14 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 '14 at 20:43

2 Answers2

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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

Community
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Ricardo
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4

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.

Olin Lathrop
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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 '14 at 11:38
  • Also I think there are another properties because for SMD type, they are almost equal. – Roh Jun 28 '14 at 11:41
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    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 '14 at 12:20