In the next screenshot, you can see a bunch of different momentary push buttons of two kinds:
- Printed circuit board (PCB) soldering: These used to be smaller, really tiny in some cases, and they come with little legs that allow them to be soldered through holes in a PCB. In the screenshot, they are the three on the left-hand side.
- Panel mounting: These are the three on the right-hand side in the picture. Usually, they come in a much bigger size than the PCB kind and come with bigger connections so that wires can be soldered to them. They usually come with some kind of nut so that they can be fixed to a panel.
Different momentary push buttons
Physical differences apart and looking at them from the connection point of view, we have to notice an important difference between both groups.
If you take a closer look at the PCB group or, even better, if you perform a simple search on the Internet, you will notice that these kinds of momentary buttons usually come with a total of four legs instead of simply two. Usually, the reason is to give a stronger union to the PCB group by allowing up to four soldering points, but also because they have their connections duplicated to provide a more reliable connection between both points of the switch.
This means that usually, momentary push buttons with four legs have them internally connected two by two, which looks like what is shown in the next diagram:
An internal wiring connection of a typical momentary push button
This simple feature has to be taken into serious consideration when connecting one of these buttons through a breadboard, because if we connect them in the wrong way, we could easily short-circuit the Arduino board, with subsequent bad consequences.
The first thing you should do when using one of these momentary push buttons is to identify every leg so that you know which of them are internally connected. They usually come with some kind of indication or diagram, but if they don't, you could always use a voltmeter or continuity tester to find out.
Once you have determined which legs are connected, you should always connect the momentary push button just above the centerline of the breadboard, which divides the two groups of holes in such a way that you leave two of the replicated connections out of use and ensure that the other two corresponding to the two contact points of the switch are always connected in different columns of the breadboard connections block. This way, they prevent a short circuit when you connect them to the positive rail (5V) and ground.
Also remember that this kind of circuit needs a current limiting resistor in a part of the branch that gets closed between V+ and the ground to prevent a short circuit again. A value of 10K is more than sufficient.