I have rocker switches that look very similar to this:
In my current understanding, a 2-positions rocker is meant to be an SPST, and a 3-positions rocker (see below) is meant to be an SPDT:
From this source, I find the following image showing an SPST rocker switch:
I observe here that it has only two pins. The 3-pins switch they have is actually an SPDT looking like so:
On this source, they show how to wire a rocker switch, like so:
I have a few questions coming from this:
- Why do they have the "on" label on the same side as the "power". Isn't that wrong? From the "internal construction" image (left), I would say it is the other way round.
- Is this 3-pins rocker an SPST switch? Why does it have 3-pins, whereas the second image (from the top of the post) only needs two for the (supposedly) same functionality? I guess it has to do with the ground, but I don't understand it.
- Still in the 3-pins rocker, what prevents me from using the "power" and "ground" pins as accessories and put the power on the "accessory" pin in order to use the rocker as an SPDT switch? Would that be a correct SPDT switch?
Best Answer
SPST stands for Single Pole, Single Throw. SPDT stands for Single Pole, Double Throw. The 'Pole' is the number of circuits that can be controlled by the switch at any time. So a SP switch can only power one circuit at a time, a DP switch can do 2. The 'Throw' is how many 'on' positions it has (I am 90% confident on this, feel free to correct me).
So: An SPST switch you will only get an On/Off whereas if you had an SPDT switch, you could get a switch with 2 On positions and only have one circuit powered at any time, so you would try and find an 'On/On' SPDT switch.
Bonus answer: If you still wanted to use a switch for this, you could search for an 'On/Off/On' SPDT switch which will only power up 2 circuits (one at a time) but the middle position will be the 'Off' position, so gives you that 'break before make' feel when switching between your circuits.
Also, rocker switches can be SPST or SPDT. A quick search on any component site will give you all the options and descriptions you need.
Hope this helps
EDIT
1 - It isn't really 'wrong' as it doesn't really matter which side you use as ground and which you use as power if you are switching between the 2. Chances are, this switch you happened to get the diagram from has some form of indication (such as a 'red' part of the button to show ON) that means you would connect the power to this side.
2 - A 3 pin rocker is usually always going to be an SPDT switch, unless one of the pins is disconnected completely. Please see my previous answer for an explanation on how these switches work and you should get an understanding of it. And if you just want an on/off switch, all of these could do it, depending on how you wire it.
3 - Nothing stops you from using the middle pin as power and using either side to connect to different circuits. As I said in reply to your first question, you most likely happened to get a switch diagram of one with indicators on it, whereas you can buy blank looking ones too. Again, read my description and you can see that it doesn't actually matter, however, most of these datasheets and examples will have to show you something, they can't give an example and say 'it doesn't matter what you wire where' can they?
Again, I hope this has answered your (revised) question.