Rotary switch to connect wiper to output contacts cumulatively

Question

Does this exist?: A mechanical rotary switch that - as it's rotated from position 1 to position N - connects the wiper to the contacts cumulatively rather than only one at a time.

For example, imagine a 1-pole 3-way switch with the following twist:

• In position 1, the wiper is connected to the first contact only (so far so normal);
• In position 2, the wiper is connected to the second AND the first contacts at once;
• In position 3, the wiper is connected to the third, second AND first contacts at once.

Reason for asking: I want to create a variable bass-cut tone control in an audio project. A cumulative rotary switch as described above would allow a number of capacitors to be progressively connected in parallel. (Please don't point me at alternative ways of making tone controls - I'm aware of circuits such as Baxandall, etc.)

Since this is an AC application I don't think I can rely on diodes.

Since composing this question I stumbled upon a web page that says "Rotary switches can also be designed to have many contacts happening at once on a single switch position." So it sounds like what I've describing is an example of that. But are such switches available to hobbyists?

I also read here that a multi-pole switch can be wired to achieve this. Sounds extravagant and, I confess, the way it would need to be wired is not leaping out at me.

Answer 1

You're looking for a rotary wafer switch.

Image source: India Mart.

The wafers on these are typically available in 1p12w, 2p6w, 3p4w, 4p3w and 6p2w variants. You probably want 12-way wafers to give you ten or twelve settings.

Posn A B C D E F G H I J
   1 
   2 =
   3 = =
   4 = = =
   5 = = = =
   ...
  10 = = = = = = = = =
  11 = = = = = = = = = =

... where = is a connection through that layer.

If you're trying this I suggest a big knob so that you have enough leverage to turn it.

Answer 2

All you need is a two pole rotary switch with three positions.

The first capacitor is always connected, so the rotary does not have to do anything with it.

So rotary only ever needs to connect zero, one or two additional capacitors.

First position, both extra caps disconnected.

Second position, only pole 1 connects extra capacitor 1. Pole 2 keeps extra capacitor 2 disconnected.

Third position, pole 1 connects extra capacitor 1 also in this position. In addition, pole 2 now connects extra capacitor 2.

Answer 3

This is how to wire up the standard rotary switch in case Transistor's wafer switch suggestion is unattainable for whatever reason. You could also try wiring up the capacitors in series and having the switch reduce the capacitance as you add more or use a single capacitor and have your (I assume) resistors ganged on the rotary switch. You could probably get more consistent steps that way since resistor tolerances are generally tighter than capacitor ones.

Answer 4

Yes they exist. For example in an old audio amp I repaired recently there was a switch like that, but with a wider contact (arrow) so it hits several contacts at the same time. This was used to enable one or both speaker output terminals.

Same principle for a wafer switch:

However... a wider wiper that spans several contacts will probably be special order.

You could make a PCB rotary switch, like in multimeters:

This looks like a good option for DIY because you can just print the pattern you want. Then you can mount the spring contact wiper on another PCB that rotates relative to the other.

Wiper suggestions: one two three four

I don't know if the contact will be reliable enough with vibration though. If it is intermittent, it will produce unpleasant sound.

Failing that, you could just use a row of toggle switches, or a simple rotary switch driving CMOS analog switch chips.

Answer 5

You could use a gray coded encoder for that. Once upon in the time (perhaps I could find a document) I have already computed standard resistors and excel table, to be used like a potentiometer. So it is doable.

Answer 6

Here's the schematic for the multi-pole, multi-way switch option.

Using a single-pole, multi-way switch would simplify the wiring.

Various combinations e.g. 4-pole, 3-way or 1-pole, 12-way are available in the same package.