Looking for Rotary DIP sw. with isolated contacts

[BobW]

Has anyone ever run across a rotary style (hex or octal) DIP switch that has the contacts isolated from each other, rather than having one side of each contact commoned together? I know I could use a standard DIP switch with individual rockers for each contact for my current project, but this would be a lot more inconvenient, than a rotary type.

 

[Ramussons]

Are you looking for a "Break Before Make" contact selector?

https://www.omega.com/pptst/OSW_SW14.html

 

[BobW]

Thanks for your reply, but I think you've misunderstood what I'm looking for. A DIP switch is a tiny little thing that mounts on a printed circuit board, and generally costs under a dollar. This is the kind of thing I'm looking for, except that I don't want the contacts commoned.
**broken link removed**

 

[Ramussons]

I think you are looking for something that behaves like the above.

AFAIK, the nearest you can get is a 3 position Selector switch like the ones used in Radio/Casettee/CD player combo, or in sliding Band Change switches. The pins in both are likely to be DIP spacing.

Something like this ... (this is 6 pole, 3 way)

You will need the work out "number of poles" and "ways" depending on your requirement. You may be lucky to get a 10 position switch - there were / are 10 band radios still available.

 

[AnalogKid]

I've seen the kind of slide switch described above with as many as 6 positions, but again it is a small slide switch, not rotary. Another possibility is a crosspoint matrix switch, a flat thin thing mayve 1.5" square with 10 or 16 sliders. As the levers moved they made up one x row with one y column. Semi-isolated contacts depending on the selections, but not rotary. Rotary dips are built to replace standard dips in one specific application, which is why they all function the same way.

ak

 

[BobW]

Rotary dips are built to replace standard dips in one specific application, which is why they all function the same way.

And yet, it's easy to find a regular DIP switch with completely separate contacts. Anyway, I guess I'll just have to use a regular DIP switch. It will function just fine, but it will be a bit more inconvenient, because the user will have to step all of the binary combinations to get the thing set properly.

I guess I should explain what I'm trying to accomplish, and maybe someone can suggest another alternative. This is part of a filter circuit. I have four small inductors: 82, 150, 330 and 680 µH connected in series. Note that each value is roughly double that of the previous value. I want to connect one switch contact across each inductor so that I can short it out, hence the need for non-commoned contacts. By shorting out various inductor combinations, I can get inductance values from 0 to 1242 µH in steps of approximately 82 µH. If I could find a hex coded switch with separate contacts, then the inductance values would incrementally increase from one position to the next, which would make it much easier to adjust. Adjustment of the filter is normally a one time event during setup of the filter. Once it's been set up, it won't likely be touched again, so I'd rather not invest in a fancy switch designed for millions of operations.

 

[AnalogKid]

Can you afford signal-level solid state relays? Photo-MOS et al have fully isolated MOSFET outputs that can carry 1 A. A standard rotary DIP switch could drive the LEDs.

Or change to different inductance values and have a standard rotary DIP switch connect them in 15 *parallel* combinations (plus 0).

ak

 

[BobW]

I'd thought of relays, but decided that it was overly complex, plus it would take up excessive PC board space.

Or change to different inductance values and have a standard rotary DIP switch connect them in 15 *parallel* combinations (plus 0).

Paralleling inductors really doesn't work very well, but I guess I should have a look and see how consistent the the increments could be.

There is also the option of using a 1P16T DIP rotary switch and just use 16 individual inductors. The inductors are cheap enough; it's just the PC board space that would be an issue.

 

[AnalogKid]

Since the signal frequency, amplitude, voltage, current, and impedance still are unknown, all potential solutions are just piles of guesswork.

A CD4066 analog switch has three independent SPST CMOS switches in one DIP. I guess that might work.

ak

 

[BobW]

Frequency range is 0.5 to 2 MHz. Current is under 5 mA. I don't know what the maximum voltage will be at the moment. Due to resonance it could be significantly higher than than the supply voltage which is 12 volts. However I did use a regular DIP switch in an early prototype of the circuit, and had no problems with it.

Good news: After my last post, I had a look at the parallel inductor arrangement, and after playing with the numbers in a spreadsheet, it looks as if I can get quite a good workable range. The increment between steps is no longer constant, but will be a constant percentage, which may in fact be better. I need to play with the numbers a bit more.

 

[Mikebits]

Since this is used as part of a filter, and essentially the switch is to short out the inductor. In this situation the switch is ideally a piece of wire presenting no impedance or resistance, but in the real world there will be some impedance and some resistive component, but at the frequencies mentioned the effects are negligible. Now using a analog switch such as the very obsolete CD4066, there is a very real impedance and resistive component thus not presenting a near short circuit, and predicting the additive properties of inductance difficult to say the least. In this circuit as was explained, I do not think a analog switch would work very well without doing a lot of math.

 

[BobW]

In the end I came up with this arrangement using a standard hex coded DIP switch:

It gives the range I need with reasonably consistent step increments. The table shows the inductance between terminals A and B for the different switch positions. The only glitch is that it goes open circuit at position 8, but that's not a show stopper.

 

[Mikebits]

That looks good, my only suggestion here is keep the traces short as possible. Added inductance of the traces plus switch inductance will affect your calculations. You should look at the data sheet for switch inductance/capacitance. If you wanna be accurate. Party on dude.

 

[Mikebits]

Upon further consideration something occurred to me. In the case of position 0, this could present an issue depending how the points A and B are placed in a circuit. If for example the points A and B are part of a feedback loop, position 0 would be open loop, and some circuits do not like open loop. Without seeing the circuit myself, you should look at your design and determine what if any effects points A and B will have on your circuit if they are open.

 

[BobW]

It will be a simple parallel resonant circuit, and no feedback. There will be a small trimmer capacitor connected across terminals A and B. So there will always be some finite reactance in the circuit.