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 Forum index » DIY Hardware and Software
Differences between different rotary switches
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rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Thu Jun 05, 2014 2:57 pm    Post subject: Differences between different rotary switches Reply with quote  Mark this post and the followings unread

I am not sure I understand well the differences between the different rotary switches available.
What could I do with a 1-pole-12-position rotary switch ?
What could I do with a 2-pole-3-position rotary switch ?
What could I do with a 3-pole-4-position rotary switch ?
The example does not have to exist, it is simply to help me understand why only 1 pole for instance or why not 4-pole-4-position.
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analog_backlash



Joined: Sep 04, 2012
Posts: 391
Location: Aldershot, UK
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PostPosted: Thu Jun 05, 2014 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Rogerlatur.

I'm not sure if I fully understand the question, but here's my guess at an answer!

The most common rotary switches are based on the same pattern of contacts. There are 12 around the outside labelled 1 to 12 and 1, 2, 3 or 4 near the centre labelled A to D. The letter labelled contacts are the poles and the numbered contacts can be connected to these by rotating the switch. There are 4 possible types:

1) 1-pole-12-way
2) 2-pole-6-way
3) 3-pole-4-way
4) 4-pole-3-way

The first only has pole A, which when rotated can connect to each pin 1 to 12. The second has 2 poles, A and B. A can connect to pins 1-6 and B can connect to pins 7-12. The third has 3 poles A, B and C. These connect to pins 1-4, 5-8 and 9-12 respectively. The fourth has 4 poles A, B, C and D which connect to pins 1-3, 4-6, 7-9 and 10-12 respectively.

Additionally, rotary switches have a stop adjustment (hidden under the nut and lock washer) which keys into holes marked 2 to 11 (you remove it if you need all 12 positions). If you put the stop into hole 2 say (after turning it fully anticlockwise first) it will only allow movement to 2 positions. If you do this on a 3-pole-4-way switch say, then A will connect to 1 or 2, B to 5 or 6 and C to 9 or 10. Using the right switch in the right stop position thus gives you a large number of possible switch configurations.

There is no reason (in theory) why you couldn't have a 4-pole-4-way switch, but they are not commonly available (but I'm sure they're out there somewhere Very Happy ).

I hope that helps a bit.

Gary
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rogerlatur



Joined: Dec 22, 2012
Posts: 118
Location: france

PostPosted: Fri Jun 06, 2014 12:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you very much Gary. Very clear explanation ! thumb up

What I was ignoring till now is the other way around, like using the 1-4 as 4-1. This is what I was missing (no comment !), wondering what to do other than adding some resistors between each position and being very limited with its use.

I found this morning a document online with a couple of examples too.
For those who might be interested:
http://info.ee.surrey.ac.uk/Teaching/Labs/Documents/RotarySwitchHowTo.pdf
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electrotech



Joined: Apr 24, 2013
Posts: 12
Location: Scotland

PostPosted: Fri Jun 06, 2014 2:09 am    Post subject: Reply with quote  Mark this post and the followings unread

One other thing about rotary switches you need to be aware of is the differences between make-before-break (Shorting or 'S') types and break-before-make (Non-shorting or 'NS') types.
If you were using, for example, a 1-pole 12-way switch to select one output from 12 different sources you would use a 'NS' type.
If you used an 'S' type two of the sources will be momentarily shorted together as you turn the switch.
This might not matter if the sources have current limiting resistors in their outputs, but it could matter if they have a low impedance output directly from, say, an op-amp.

Andy
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analog_backlash



Joined: Sep 04, 2012
Posts: 391
Location: Aldershot, UK
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PostPosted: Fri Jun 06, 2014 2:52 am    Post subject: Reply with quote  Mark this post and the followings unread

rogerlatur wrote:
What I was ignoring till now is the other way around, like using the 1-4 as 4-1. This is what I was missing (no comment !), wondering what to do other than adding some resistors between each position and being very limited with its use.

Do you have an example of what you are trying to do here? I understand (I think) that you want to use the switch "in reverse" i.e. 4 inputs, 1 output, but I'm still trying to work out the resistors bit (probably just me being stupid!).

electrotech wrote:
One other thing about rotary switches you need to be aware of is the differences between make-before-break (Shorting or 'S') types and break-before-make (Non-shorting or 'NS') types.

Very good point btw electrotech. I wrote this late last night when my brain wasn't fully working and I forgot to mention the make-before-break/break-before-make options.
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