This is a slightly overexplained series of posts about wiring up switches. Feel free to skip this if this is too basic for you. I’m just going through how to wire up some basic switches, namely SPDT, DPDT and 3PDT.
In this post I’m going to cover basics and demonstrate how to wire-up switches on a breadboard with some LEDs. I’m mainly focusing on Single Pole Double Throw (SPDT) and Double Pole Double Throw (DPDT). I will follow up with further posts very shortly.
If you just can’t wait, here’s the video:
The switches are simple things – at least in theory. However, there’s a surprising amount of terminology, variety of switches and nuances of their operation. Here’s what is covered in this post:
In the above diagram, there is a SPDT switch – marked as SW1. Single Pole Double Throw simply means that we have a single common pole and two connections (I marked them IN for the common connection, and OUT1 and OUT2 for two contacts). In one position IN and OUT1 are connected, and at the same time OUT2 is disconnected, in the other IN and OUT2 are connected, and OUT1 is disconnected.
Now, I used slightly unfortunate designation here. Common connection can be our input jack tip, or output jack tip for example, but I hope you get what I’m trying to say here.
The DPDT switch marked as SW2 – is equivalent to two SPDT switches controlled by the same mechanism. They are electrically independent, but since they are controlled with the same mechanism (push button, toggle, dip switch, whatever) the two parts of the switch are always in the same position.
In the above diagram I showed alternative symbol at the bottom. Those two symbols are equivalent, but the bottom one is usually handier to use. The bottom one just splits the switch into two SPDT units, SW2A and SW2B, but it’s the same switch.
Here’s how to wire them up to try out how do they work:
In the above diagram, in one switch position, green LED is on, in the other, the red one is on. The switch controls which LED is in complete circuit. LED needs to be connected to supply and ground to illuminate. The switch simply connects one of the LEDs to the ground and the other one is left disconnected – thus, the disconnected circuit is not complete, so LED does not illuminate.
The above diagram for DPDT switch is exactly the same as for the SPDT, just I have everything doubled. You can see if you breadboard this how the green and the clear LED are turned on or off at the same time, and how the red and the yellow LED are turned on or off at the same time depending on the switch position.
That’s really it for this basic post. This might be useful if you’re just trying out breadboarding since it gives very visual circuit to experiment with. If you look at the video embedded at the top – I show how I wire-up my latching push button that I use for most of the videos.