Hello Everyone,
I'm working on a project where I need a variable resistor that can physically change in size.
Think of it as the slider on a media player and at any point it is possible to 'click on' a new slider next to the old one.
I'd prefer it if the new slider wouldn't change the maximum possible change in resistance. It would be better if when the 'slider button' would transist from one slider to the other the resistance would change to the standard maximum resistance of that slider and would decrease from that point onward.
I don't need a smooth transition in resistance because I am reading the value with a microcontroller and I can solve this with programming. I do however need a smooth transition of the physical slider button.
Does something like this exist? or is it possible to make one myself by using existing sliders?
Any help is appreciated

 

Hi, Rob -- welcome to AAC!

Your description is a bit confusing. What do you mean when you want the variable resistor to change in size? On first reading, the take is you want the linear dimensions of the device to change (this is what I think of when I read "physical size"). Of course, this doesn't really make sense and I doubt a suitable such device exists. So then I conclude you must want the resistance of the device to change somehow. You use "media player" to describe the behavior, but that leaves me in the dark because I don't know how a "media player" is supposed to behave.

Why don't you explain your application and what you're trying to accomplish (there may be better ways than what you have in mind). Also, describe the operation of the device you want with physical numbers -- the software folks call this generating a use case. It helps others understand the problem better.

 

I don't know how to make a 'use case', but I think it's easier if I draw it out:


I need a slider (variable resistor) which can be extended by adding a new 'slider' to it. (it should be able to extend multiple times).

I want to be able to determine the position of the slider from the output received by my Arduino.

 

You need to explain your actual intent.. What exactly are you trying to do... People here might have other ideas to accomplish the end goal...

You aren't going to find your expandable variable resistor slider.. How about the danger shield http://www.sparkfun.com/products/10115

 

I'll try to explain my concept:
I want to make a tangible slider that allows me to control media on my computer or a different device. Think of the sliders at the bottom of media programs like VLC media player and windows media player, you can drag the buttons of these sliders around to a certain time period so the media starts playing from there. I want to make these sliders tangible

I want to make a media player that has it's sliders 'replaced' by a tangible, physical slider. For example, if the block of my first drawing would represent a song the slider would represent the time of the song. So placing the slider button at the beginning of the block would let the song start from the beginning, and placing the slider button in the middle of the block would play the song from that point.
However, I want my slider to be expandable. So if a second block (representing a new song) would be added to the first block like in my drawing the slider should be 'merged'. The slider button should be able to move freely between the blocks. So when the slider button would be placed near the end of the first block it would first finish song1 and then would continue playing song 2 from the beginning. By connecting several blocks to each other a tangible playlist can be made.

The slider button should be able to get moved to a certain position by the user. Once it's placed it should automatically start moving to the right until it hits the end of the last block. I should be able to read the position of the slider with my Arduino so I can play the song accordingly.

Letting the slider button move on it's own might be tricky so for now only being able to move the slider button manually would be sufficient. I'm not good at putting my concepts into words so I hope this was understandable

 

Well back to the drawing board for you then...

 

I can't think of a practical way to implement something like this in an electromechanical device that would be reliable AND not cost-prohibitive.

It would be far easier to implement in GUI software using a touch screen; something like an Iphone.

 

I'm not sure you will find the hardware that meets your desires but I think that by using computer programming, you could accomplish something along the lines of what you stated. For example, if only one song is "selected" then the "slider" would act as you described(slider moved to middle goes to middle of song, slider moved to end goes to end of the song, etc.) However, if you add another song to the playlist, then the scope of the slider encompasses both songs...so now the middle position of the slider corresponds approximately with the beginning of the second song...

Would something like that fit your needs or do you want multiple "sliders"?

 

I don't know about keeping the total resistance the same, but you could use the voltage divider effect.
I don't know about moving it around, and I can't think of any ways to make it move on its own, some sort of electromagnet and a spring maybe? or a tiny, tiny motor/servo?
I also cant think of any ways to make such a device in a single unit (at least a small one) without some percision machining or stereolithography and tiny surface mount soldering. Noone likes that.

 

I can't think of a practical way to implement something like this in an electromechanical device that would be reliable AND not cost-prohibitive.

It would be far easier to implement in GUI software using a touch screen; something like an Iphone.

Hmm, the physical slider button is pretty much a requirement for my project. so a touch screen wouldn't be an option for me.

I'm not sure you will find the hardware that meets your desires but I think that by using computer programming, you could accomplish something along the lines of what you stated. For example, if only one song is "selected" then the "slider" would act as you described(slider moved to middle goes to middle of song, slider moved to end goes to end of the song, etc.) However, if you add another song to the playlist, then the scope of the slider encompasses both songs...so now the middle position of the slider corresponds approximately with the beginning of the second song...

Would something like that fit your needs or do you want multiple "sliders"?

I think both the 'expanded slider' and 'multiple sliders' would be ok since I can solve that in the program I write. The only problem I can think of in the 'expanded slider' situation is that I would not be able to put more than a few songs in the playlist at a time since after a while I wouldn't be able to read the differences in resistance of the output.
For every song I need to be able to read 10 different slider positions. And I want a minimum of 20 songs in the playlist. If the 'expanded slider' method can handle that it would be great

I don't know about keeping the total resistance the same, but you could use the voltage divider effect.
I don't know about moving it around, and I can't think of any ways to make it move on its own, some sort of electromagnet and a spring maybe? or a tiny, tiny motor/servo?
I also cant think of any ways to make such a device in a single unit (at least a small one) without some percision machining or stereolithography and tiny surface mount soldering. Noone likes that.

Yeah I was thinking about a small motor/servo as well, in combination with some sort of cog and a rail.
Size wise: I was hoping on something with a max height of 3,5 cm, max length of 4,5 cm and the width would be the width of the slider (thinking about 6,3 cm for that).

 

mixing-board automation!

old recording desks would chase the timecode on an audiotape allowing for the position of all your sliders to be recorded and played-back.

these days, there are several midi-compatible control surfaces with motorized faders for use with logic, protools, etc.
last time i checked the bcf2000 b-control fader was the cheapest option.
i have one and have used it quite extensively with a certain max/msp environment. it was quite simple to map the relative position of your audio or video playhead to the position of the slider:

slider bottom = beginning of song
slider top = end of song
middle = middle

the mapping is relative to the length of the file... that what VLC does also.

some kind of absolute relationship of slider position to a time value?
that might be tough depending on what your going for... might be easy.... might be as simple as just making all your sound files the same length, or mapping across several faders as you mentioned.
using a relative position/time relationship works awesome in my experience... if your tracks don't get too long.

...just a note about the bcf2000 thing. the fader automation motors only worked with specific software geared to audio production... at the time when i was using this, i hadn't actually heard of anyone who had been able to use the motors with max/msp, supercollider, etc.

maybe i didn't look hard enough, or maybe this has all changed.

...oh... and i'm sure that you must be able to buy normal, individual motorized faders... the kind used in big audio desks... maybe that's something for you? or maybe it's way more fun to just make your own giant version : )

 

While not a potentiometer, how about adapting a DRO(digital readout) scale? DRO's are used on machine tools to measure where the cutter is in regards to the part. Here is a short text on how they work and a company that sell replacement scales;http://www.zsinstruments.com/scales_about.aspx

You would still have to come up with a way to time each song with a place on the scale. But it would be easier than referencing a resistance to a time, because the scale will give a definite point and place in a linear manner. They are available in almost any length you want also.

 

easiest... i think just modifying something like this:
http://www.jlcooper.com/_php/product.php?prod=fm4100
like just putting it in a new box essentially.

but for awesomeness:
http://www.pennyandgiles.com/Standard-Motorised-Faders-pd-66,3,,.php
they even come with switches built into the knobs : )