In the same “note to future self” vein as my recent hexagon math blog post, I’m writing this today more as a note to myself than an informative or fun blog post for the regular reader.
With increasing frequency, I have started working with these little through-hole micro switches:
As you can see, there are four pins, two pair. When at rest, the two pins of each individual pair connect together, but the two pairs are not bridged. When you push the button, the two pairs bridge. Effectively, all four pins connect together. In electronics terms, it is a momentary single-pole, single-throw (SPST) switch, it just happens to have two legs for each pole instead of one.
Now, how would you intuitively group the two pairs of pins? In the above picture, it reasonably feels like the two on the left should be one pair and the two on the right should be the other. Pushing the button would bridge the pairs. BUT YOU’D BE WRONG! It turns out that the pairs are across the top and across the bottom. The schematic for the above picture looks like this:
Every time I work with these switches, I have to pull out the multimeter and test which legs are paired. From now on, I will just refer to this blog post. (Or, more likely, the act of writing this blog post will have cemented in my mind how the pins are configured.)