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:
2-leg:
Why do they use 4-leg in many cases? for example, in mobile phones, in many cases, they use 4-leg. look:
Electronic – the difference between 4-leg and 2-leg momentary tactile switch?
switches
Related Solutions
Perhaps this drawing will help.
As you can see on the right hand part of the part of the diagram pins 1 and 2 are connected together. Pins 3 and 4 are connected together and the switch action is between these pairs of pins.
Using a multimeter set to low ohms (resistance) you should find that the two sets of pins that are short circuit. These correspond to pins (1,2) and (3,4) in the diagram.
To get a switch action you need to connect one side of your circuit to pins 1,2 and the other side to pins 3,4. Of course you do not have to connect both pins on each side of the switch. It will work by connecting 1 and 3 or 2 and 3 etc.
a data sheet can be found here http://www.omron.com/ecb/products/pdf/en-b3s.pdf
All mechanical switches have the potential to bounce, and most do at least some of the time.
That's exactly what is happening. You need to add a debounce circuit. The easiest way is something like this:
simulate this circuit – Schematic created using CircuitLab
The RC slows the switch transition down, and the Schmitt trigger gate cleans it up so there is only one transition each way, thanks to the hysteresis.
Best Answer
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:
In other words, the additional shorted terminals are meant to be used as jumpers.
I have built one myself (see below). Those boards are a lot of fun to route.