multi wiper potentiometer? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: September 27, 2024, 11:40:51 pm
content: Does this exist? has anyone seen one?its possible to put multiple wipers on a single resistive path.

author: Benta
author_rank: Super Contributor
timestamp: September 27, 2024, 11:46:50 pm
content: No idea what you mean.Post a sketch or a drawing.

author: Smokey
author_rank: Super Contributor
timestamp: September 27, 2024, 11:48:25 pm
content: Like for a 10 turn pot that you have set to 5 turns, instead of the single wiper being at 50% the two wipers are at 33% and 66%?

author: coppercone2
author_rank: Super Contributor
timestamp: September 28, 2024, 12:45:41 am
content: yeah , like for some weird divider

author: Kim Christensen
author_rank: Super Contributor
timestamp: September 28, 2024, 12:46:42 am
content: The only thing I've seen are audio pots with a "loudness tap"... This isn't multiple wipers on a single element though.

author: squadchannel
author_rank: Frequent Contributor
timestamp: September 28, 2024, 12:52:00 am
content: There were a lot of those special ones in old japanese audio amplifiers(sansui etc...).ALPS's square potentiometers. had an "特" mark. There were many kinds of them.https://nw-electric.way-nifty.com/blog/2012/11/post-b2fa.html

author: coppercone2
author_rank: Super Contributor
timestamp: September 28, 2024, 01:01:56 am
content: oh damn I wrote it wrong, I meant multi wiperthat is also interesting to have multiple taps, but I meant multiple moving arms

author: CaptDon
author_rank: Super Contributor
timestamp: September 28, 2024, 01:32:49 am
content: There is a style of multi-wiper pot known as a sine/cosine pot. First, think of a continuous turn pot with a 360 degree resistive element. The top of the circle is fed with a positive ramp sawtooth, the bottom of the circle is fed with a negative ramp sawtooth and the two sides (left and right) are at ground or 'return' so to speak. Now, there are two wipers spaced 90 degrees apart, one called sine, the other called cosine. These were used in radar to generate the PPI (Plan Position Indicator) C.R.T. scan voltages. They were continuous turn with no stops and tracked the rotating antenna via a selsyn syncro motor resolver. I believe I still have one in my junk box. They were always incredibly expensive and designed to be flawless through at least a million revolutions. Scanning radars usually run at 30 RPM or less but there are some oddballs that run way faster. Very long range scanning radars turn much slower such as weather radars. (In case you wanted to estimate the life of a million turn service life pot) The sine / cosine function was done more cheaply (but mechanically complex) with a pair of normal pots that had roller followers riding on an offset cam lobe and a spring to keep the followers against the cam.

author: TimFox
author_rank: Super Contributor
timestamp: September 28, 2024, 01:46:03 am
content: In grad school, we needed DC voltages (pos/neg sine and pos/neg cosine) to adjust electron optics.Those sine/cosine pots were available surplus from companies who dealt with old-style servo equipment.They are covered in the Radiation Laboratory book series for radar applications, such as in CaptDon's post.

author: coppercone2
author_rank: Super Contributor
timestamp: September 28, 2024, 01:51:28 am
content: ah that makes sense, but what I was imagining is multiple shafts on the same resistance substrate. So you have two independent inputs to a common substrate (weird)sine/cosine pot does fit the description thoughsome kind of computer function or ratiometric thing could be done with this? not sureyou could build them so they collide into each other to short them out if you please with contacts on the side