Shorting rotary switch only shorting in one direction - Page 1
Forum section: electronics / beginners

author: rqsall
author_rank: Regular Contributor
timestamp: June 22, 2018, 07:02:19 am
content: Hello all,I bought these switches:https://www.aliexpress.com/item/2pc-High-quality-RS26-3-Pole-Position-4-Selectable-Band-Rotary-Channel-Selector-Switch-Single-Deck/32822295045.htmlaccording to the datasheet at the bottom of the page, they are shorting. It doesn't matter much for my application, but I figure I'd test it anyway. So I set my Fluke 8010A to ohms range, connected the common to the pole connected to position 1, 2, 3 and 4. Connected the other multimeter terminal to position 1 and 2 and slowly turned the switch to see if the resistance would rise when switching. Well, when switching from position 1 to 2, it does, but switching from position 2 to 1, the resistance stays 0.Has anyone seen this before?Am I even doing this correctly? What would be a better way to test?

author: mikerj
author_rank: Super Contributor
timestamp: June 22, 2018, 11:39:30 am
content: Just connect the meter between any two adjacent poles (1-2, 2-3, 3-4). There's no need to connect to the common terminal.

author: rqsall
author_rank: Regular Contributor
timestamp: June 22, 2018, 12:25:27 pm
content: Quote from: mikerj on June 22, 2018, 11:39:30 amThen the meter reports open circuit in either position. I assume you mean position rather than pole? With common terminal I meant the common terminal of the meter.

author: JS
author_rank: Frequent Contributor
timestamp: June 22, 2018, 06:51:55 pm
content: Quote from: rqsall on June 22, 2018, 12:25:27 pmWhile the meter is connected as described it should only close shortly as you switch positions, not once sitting on any position. This is what's called make before brake close the next connection before opening the last one used to reduce switching noise in some configurations or acoid having open circuit on the wiper, as opposed to break before make which opens the last contact before closing the next one, used to prevent shorting between different terminal positions, like selecting different low impedance drivers to a single receiver. This last one is the default, more usual ones.JS

author: rqsall
author_rank: Regular Contributor
timestamp: June 23, 2018, 08:41:02 pm
content: Quote from: JS on June 22, 2018, 06:51:55 pmWith the switch in position 1 and the ohm meter connected with its common terminal to the appropriate pole (the one that is switched by postion 1, 2, 3 and 4) on the switch and the other ohm meter terminal on position 1 connection, there should be 0 ohms right?Now if position 2 is connected to position 1, then I should not see open circuit at any time when Islowlymove the switch from position 1 to position 2. However, I do see open circuit for a short moment, but I don't see this same open circuit when I then move the switchslowlyback to position 1 from position 2. In that case, there's continuity the entire time.

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: June 23, 2018, 09:02:13 pm
content: Hi have some of these older on my archive and i found an interesting how to for the switch:http://info.ee.surrey.ac.uk/Teaching/Labs/docs/RotarySwitchHowTo.pdfHave a look at that and see if it suits your purpose.

author: JS
author_rank: Frequent Contributor
timestamp: June 23, 2018, 10:43:31 pm
content: Quote from: rqsall on June 23, 2018, 08:41:02 pmThere should be continuity between both at some point, if you test with two meters, one from pos 2 and one from pos 1 both to common, there should be a moment where both are shorted and no moment when neither of them are shorted. A scope and a two pullup resistors will show this better, using two channels you should see it happening, going in any direction. It doesnt matter if one way is longer than the other.If the behaviour is not that you should get better switches...JS

author: rqsall
author_rank: Regular Contributor
timestamp: June 27, 2018, 09:24:25 pm
content: Quote from: JS on June 23, 2018, 10:43:31 pmThank you very much for the oscilloscope trick! I had to struggle to rotate slow enough to see it, but I can confirm that my first assessment was incorrect and the switch makes before breaking when turning in either direction. Scope set to both traces at the same vertical position when grounded. Only one trace is seen at supply voltage on turning the switch for a short moment, meaning both channels are measuring supply voltage.Glad I got what I paid for