A Few Words on Plastic Rotary Switches

Plastic rotary switches are supplied in various forms and when properly used, are highly reliable. Typically these switches are supplied in single pole 12 position, 2 pole 6 position, 3 pole 4 position, and 4 pole 3 position types.

However, these are only the basic forms, and a clever travel limiting mechanism allows each of these basic forms to be varied to suit the user. This detent arrangement can be seen in the photos, and consists of a metallic collar with a protuding stop (B), which can be fitted into a series of holes (C) in the switch body.

Taking a single pole 12 position rotary as an example, this mechanism allows the user to select any number of switch positions from 2 to 12. Further, by placing the stop into the appropriate hole, switch rotation can start clockwise from pin 1, or anticlockwise from pin 12. So for example, if the user wants a single pole 4 position switch, it is simple to elect to use switch pins 1-4 or alternatively pins 9-12 to suit a front panel layout and a particular knob.

This is not the end of the story however. There are many variants of the four basic forms because the manufacturer can play games with where the anti-rotation stop (A) is placed on the switch body relative to the common terminal(s) and switch contacts. The label of a common variant of the single pole 12 position switch (6C1) can be seen in the second photo of the switch rear.

Anyway, the bottom line is this. Despite what some people are saying on the internet, because of all this built in flexibility, it is NOT necessary to pull the rotary switch apart to make the switch line up electrically with the pcb pattern. Provided there are a sufficient number of holes provided in the pcb for the anti- rotation feature on the switch body (the analyser pcb has 4 holes) it is completely possible to use any single pole 12 position variant of the switch in this project. All that is needed is an ohm meter, and a little intelligence and patience.

As a final comment, DO NOT overexpose these switches to soldering heat. Plastic has a memory. It started life as a moulding pellet, and will return to this form if overheated. Make your soldering quick and clean with a short cooling off period between joints on the pins. Holding a pin at soldering temperature for more than 15 seconds almost guarantees an open circuit switch.