building a linear slide potentiometer?

Or just buy one. Take it apart. Mail the parts to yourself and start building it!

HI MAD SCIENTIST, APART FROM THE FACT YOU COULD BUY ONE, AND SEE HOW THEY DO IT, YOU COULD PERHAPS USE A VERTICAL TUBE FILLED WITH WATER, AND ONE ISOLATED WIRE WITH END STRIPPED TO THE BOTTOM, AND A METAL WEIGHT ON AN OTHER WIRE ,THAT CONNECTS TO YOUR HORIZONTAL OR VERTICAL SLIDER. ADD SOME CHEMICALS TO ADJUST CONDUCTION. IN MY SCHOOL DAYS THE GUYS USED A CAPPED FLUORESCENT LIGHT THAT WAY TO CONTROL THE SPOTS IN THE PARTY.

KEEP CLICKING HERE FOR

MAYBE THE CHEMICALS SPILLED INTO YOUR CAPS LOCK KEY?

On a sunny day (Fri, 09 Nov 2007 08:45:58 -0800) it happened snipped-for-privacy@netzero.com wrote in :

NO THERE IS ONLY COOKIES THERE.

Thanks for the tip. This probably wouldn't work for me because it's too expensive ($47) and it's gear based (too hard to build, easy to break). I'm just wondering what materials you could use, to lay out a strip. See the drawing below (view in fixed-width type such as courier)

slider wired to signal out the farther to the right it's moved, the more resistant material the signal has to travel through thus higher resistance v ___ | signal in->==================== ^ strip of resistant-but-somewhat- conducting material

I would be looking for something that would be pretty durable and cheap & easy to build. Something involving liquids wouldn't work.

Thanks

What about liquids that become solids? Epoxy resin, roe instance. If you could come up with a mold for a strip of epoxy loaded with graphite powder, you might be able to make a slightly conductive strip. Then use plain epoxy to glue that to an insulating backing strip.

SOUNDS DELICIOUS. I CAN HAS COOKIES PLZ?

On Fri, 09 Nov 2007 17:12:27 +0000, mad.scientist.jr wrote: On Fri, 09 Nov 2007 17:12:27 +0000, mad.scientist.jr top-posted:

...

If it's only for demonstration or education purposes, split a pencil lengthwise.

Otherwise, find some enameled nichrome wire and a plastic stick; wind the wire around the plastic stick; glue it in place, and sandpaper off the enamel on one side, to contact your slider. (that's how real trimpots are made.)

Good Luck! Rich

E...

snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@o3g2000hsb.googlegroups.com:

Antistatic bags. The black ones with low resistance, cut into strips of the length you want, and cut narrow enough to get the resistance you want.

They're soft so you want a wheel on the slider to reduce friction, so that gentle compression keeps the wheel in contact with the plastic.

snipped-for-privacy@gmail.com wrote in news: snipped-for-privacy@d55g2000hsg.googlegroups.com:

I once made a long linear "pot" for a yoke for Flight Simulator. I used an adjustable power resistor and a spring mounted roller attached to a square slide tube (hobby brass). It worked great for that purpose...not sure it would work for you.

Ken

how about a ~ 3 " cross diameter shelve mounted on a shaft of a pot? the shelve would have a mine steel or strong fishing line wrapped out it that connects on both ends of the linear rode movement so that it will turn the pot.. You're asking for an 8 inch travel , 8 / Pi = ~2.5 inch in width.. add a little for the fact that the pot does not do 360 degree's unless you get a rotary pot :)

then there's the option of connecting a multiturn pot on the end of the drive mechanics that is doing the traversing, Acme lead screw or ball nut screw for example.

of course, You can do what I did once, it wasn't a linear track slide but it could apply to you..

I got some large carpenter pencils and took the lead out or should I say, more like carbon .. I suppose you can buy the stuff also.. I took an old screw driver handle and stuck it in a baby food jar with turpentine and a rag wrapped around the entry point so that it wouldn't evaporate. After some time the old handle dissolve away from the screw driver making a nice pliable plastic putty more or less.. Then I mixed the ground carbon power that I made into it, using a popsicle stick as the mixer..

when you get ready to apply it in a linear track in your case for example, poor it on and lay wax paper on top where the wiper will be. The wax should allow it to peal away leaving a rather smooth surface that is conductive.. p.s. Make sure you have your end connections in the track before poring this and the mix on the carbon has to be strong verses the potted material you decide to use.

Btw, the dissolving of existing plastics is an old trick body shop guys use if they are repairing a small damaged area of the plastic interior of your car. They cut off small pieces of the same plastic so that the color and mix will match and then use the rest of the other tools they have for matcning up the textures and so on. I don't remember the chemicals they used for this. I know it wasn't turpentine but something that does the same job :)

JM

snipped-for-privacy@netzero.com snipped-for-privacy@netzero.com posted to sci.electronics.design:

That is rather a poor choice, it is motorized. How about a regular one?

Have you considered building a string pot?

How about a flat rack gear driving a circular gear mounted on a 10 turn pot? Easy mechanics.... cheap solution.......

Not a potentiometer, but an idea for a variable capacitor. It is easier to make a drawing for explaining it:

The bright parts are wood or plastics. The dark part is metal or thin layers of metal and is the capacitor. When moving the slider between the metal, the capacitance of the capacitor changes. This can be measured, if the capacitor is part of an oscillator and electronically transformed to a resistance.

A bit more complicated to build, but good for higher capacitance changes: Same construction, but the slider is metal, too, isolated from the metal sides. The two metal sides are the other plate of the capacitor. Maybe use multiple metal plates for higher capacitance changes.

Advantage: Can be built to be very long-living. Disadvantage: It could be difficult to measure the capacitance and could be influenced by environment, like temperature. But I don't think this is a major problem, because old radio tuners works very precise with something like this:

On a sunny day (Fri, 09 Nov 2007 23:04:37 -0500) it happened John Popelish wrote in :

There is an other way also. Use a LDR (Cadmium Sulfide light deopendent resistor). Connect a piece of metal with a V sized groove to the slider knob. Bulbs on one side (stabilized on DC), and LDR on the other side. Or move a mirror, etc, several solutions possible. The form of the groove sets the curve (log, lin, whatever).

Dichotomy there - your first criteria is accurate then you mention pencil lines?

Linear slide pot with a 10" travel? How about taking a light source opposite a photocell and moving the pair past a triangle shaped cutout in a light barrier?

At one end of travel light is stopped from reaching the cell by the barrier and as the source/receptor pair move to the other end the triangular cutout in the barrier lets more light past and the resistance of the cell drops - any length, no contact parts to get noisy, probably a long lifetime as long as moisture is excluded - hermetically sealed photo cells or photo transistors.

Might work with just a light source moving closer to a photocell - no barrier.

Downside - bound to be lots of development time tweaking in the cutout in the barrier to compensate for non linearity in the source/detector. Only a rheostat so it would take some electronics or a pair of detectors (one getting more light the other less with travel)

Or drop the idea of a traditional pot and use a digital pot - then you need a linear encoder or linear to rotary gear to get a pulse out to set the digital pot.

Easier to just buy what you want of have it custom fabricated. Sounds expensive, but good pots are expensive these days. They already use them in video and sound mixing studios - so someone is making them.