What are those 1 4 and 2 3 on both sides of the button? They look like having connected to same places at both ends, it looks like redundant cable to me.
So, what are they representing?
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3\$\begingroup\$ Unnecessarily visible pin numbers? \$\endgroup\$– user156429Commented Apr 29, 2020 at 22:35
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3 Answers
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Tactile switches usually have four pins, with pin pairs already connected to each other. Very often you'll see that the switch closes contact between the pins on a particular side.
Since pin numbering is typically done on alternating sides, but the contact is done between adjacent pins, you can have pairs [1,4] and [2,3] electrically connected.
Here is an excerpt from a common tactile switch datasheet (C&K PTS645):
The schematic (top right corner) shows a slightly different arrangement where the pairs are [1,2] and [3,4].
You can use a switch with either arrangement, just be sure you know which pins are electrically "normally closed" and which are "normally open" by examining the datasheet before you solder.
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\$\begingroup\$ OP, notice this part's pin numbers violate the usual "counter-clockwise from the upper left" convention. But what's really important is what numbers were assigned in the PCB footprint library you're using. \$\endgroup\$ Commented Apr 29, 2020 at 22:54
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\$\begingroup\$ @ThePhoton I thought the pin numbering on this part was unusual, too. I checked a few others (TE Connectivity and E-Switch) as well, but the three I randomly audited all used the same [1,2] and [3,4] pairs. \$\endgroup\$– JYeltonCommented Apr 29, 2020 at 23:03
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\$\begingroup\$ very nice answer, thanks. So, from this, take away for me is that there is not a well defined standard for numbering pins of these switches. Then, logical thing to do is to rely on examining internally connected pin pairs and deciding how to connect the component specifically to that particular component. \$\endgroup\$– muyustanCommented Apr 29, 2020 at 23:39
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1\$\begingroup\$ @muyustan That's correct. Standards are nice but should never be assumed. Whether you have the datasheet or not, you should be able to quickly tell which pins are doing what with a few continuity tests using a multimeter. Also note that you could very easily use a 2-pin switch and ignore the "duplicates." \$\endgroup\$– JYeltonCommented Apr 29, 2020 at 23:42
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I was induced to post this answer here because another question I started to answer was closed as a duplicate of this one.
There are two other things to consider regarding the two pins on each side connected together that are not mentioned in other answers and or comments.
- The internal construction of these switches often has the lead frame made in two pieces each of which extends to the two connection pins on either side. These lead frames extend internally to periphery contacts and a center contact that sit under a small click dome switch. The disk, when clicked down, makes contact with the mentioned contacts closing the switch. Here is a series of pictures showing construction of the typical TACT switch all the way down to the lead frame.
- Another valuable feature of the pairs of pins connected together on the switch is that it allows for the layout of matrix of rows and columns of these switches on a one sided circuit board (or one layer section of a multi-layer board). The following picture shows a layout that takes advantage of this to allow making the matrix without jumper wires.
answered May 21, 2020 at 3:55
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2\$\begingroup\$ I closed it as it was a duplicate and another question answered my question. Howeve, I especially like your second remark about the button matrix. Also, a benefit is higher stability for four pin switches (but mine is very small so no issue). \$\endgroup\$ Commented May 21, 2020 at 11:31
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Those are pin numbers.
It's useful to have them on the schematic to verify that the correct pins of the physical part will be connected to the correct places in the layout.
answered Apr 29, 2020 at 22:35
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\$\begingroup\$ Yes, of the push-button switch. \$\endgroup\$ Commented Apr 29, 2020 at 22:45
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\$\begingroup\$ ok, are the
1 4and2 3pairs the ones which are internally connected? Is this numbering a standard for tactile switches? \$\endgroup\$– muyustanCommented Apr 29, 2020 at 22:49 -
1\$\begingroup\$ The connections are as shown in the diagram. The numbering isn't necessarily standard (the numbering shown is the most common in my experience, but I'm not sure that every vendor or every footprint designer follows it). That's why you need the numbers to be on the diagram --- so you can be sure the numbering used on the footprint in the layout matches the connectivity you want from the schematic. \$\endgroup\$ Commented Apr 29, 2020 at 22:51