How can I make my own potentiometer?

Question

I want to create my own potentiometer for a project. Part of the reason is because I believe it'll be more adapted to my needs but I must admit that it seems like something really fun to do.

I've read online that the resistive part of the potentiometer is either made of Graphite or a "resistive cable". I know many good stores selling electronics component but I wasn't able to find graphite stripes to make my own potentiometer.

Another idea I had is to use a cable used for heating since they are pretty resistive by definition. I'm just not sure if it could work correctly.

So what are my options?

Answer 1

MAKING YOUR OWN VARIABLE RESISTORS

Anything conductive, accessible, doesn't oxidise, able to be "wiped" with a wiper (resistor pickup) with adequate dying "too quickly".

As this is as much for fun as anything else "too quickly" may be able to be of lower duration in time or cycles than usually.

Resistance values that you generate may be lower than not, depending on material used.

Properly "potentiometer" mans a 3 terminal device with voltage across it and a sliding voltage tap but I'll take it to also just mean 'variable resistor.

Connection to start may be with "crocodile clips or pushed in "drawing pins" / "thumbtacks/other.

• Pencil lead.

  Select an old (or new) pencil.
  Sharpen both ends.
  Measure resistance to see what sort of pot resistance you are going to get.
  CAREFULLY break open and remove the lead intact.
  May need a few pencils to get it right.
  Connect clips at either end.
  Connect ohmmeter to one end.
  Run other ohm-meter along length and note variation in resistance.

  If you connect a voltage across length then you can use a slider to puck off variable voltage with position.

• Resistance wire

  In place of the pencil lead above you can us a length of new or used resistance wire.
  Wire can be strethed tight between eg thumbtacks or nail in a piece of wood.
  Note that wood becones part of the resistor.
  New Nichome or Chomel wire canbe bought for modest cost.
  Ohms per metre varies with thickness - thinnest possible is liable to be best.
  Around 10 ohms/meter is common but higher R is possible.

  Nichrome from old heater or toaster element works.
  This may be somewhat oxidised with age and may be brittle.
  You can sand surface carefully once stretched in place.

• Butyl Rubber and friends

  Black rubber used for roofing has carbon black in it.
  Take meter and wander round sticking probes in rubber on sale and other material.
  When you find a sheet of substance that has some resistance acquire a small sample by best permissible means and cut strips to make a pot.

• Paper and salt water.

  Lay out a strip of newspaper
  Wet well but not until soggy with salt in water solution.
  Test pot.
  Note how result varies with salt concentration, degree of saturation of paper, passage of time, ...

  Try copper-sulphate in place of salt.
  Try "Epsom Salts"
  Try ... ?

• Copper wire

  !!!
  (1) Get thinnest possible bare copper wire.
  Measure resistance.
  Low but usable.

  (2) Now for a very good trick.

  Get thinnest (within reason) enamel or varnish or polyurethane insulated copper wire. Sortthat insulation can be "sanded" off with care.
  Find a "former" that is an insulator and that you can wind your copper wire on.
  Round or oval cross section is good.
  Once you have built one you will get a better feel for shape that is needed. Wind copper carefully and neatly in a long ish coil along formr. Many turns.
  Not too too many the first time.

  Wind neatly so turns stack against each other neatly. Fasten carefully at both ends.
  Now CAREFULLY use fine sand paper to sand along top surcae of coil so you expose copper on each turn BUT DO NOT TAKE OFF SO MUCH THAT COIL TURNS ALL GET SHORTED TOGETHER.

  Run a wiper along the bared copper.
  You have a wire-wound variable resistor.

• "Plastic"

  Use epoxy resin and silicone rubber.
  Fill with various amounts of carbon black, or pencil graphite or powdered metal etc.
  Make a track.
  Let set.
  Test.

  Also silver filled compound used for PCB track repair.

  Also ??? - look around you ... .

By now you should have a few other ideas.

Report back :-) !!!!

Answer 2

A long long time ago when I only had a small handful of resistors with values dependent on whatever was in equipment someone else threw away, I experimented with making my own. You'll need very different technologies for making really low and really high values, but let's stick to the more common midrange values.

What worked the best for stuff I had around was a #1 pencil trace on a piece of paper. #1 pencils were occasionally used for tests that were scored by a machine. One time after taking such a test I managed to hold on to the pencil. To make a resistor or bunch of resistors, make traces on a piece of paper, then drive small brass tacks thru the paper at the ends of the traces thru a piece of wood underneath. You can solder straight to the tops of the tacks. By changing the length, width, and amount of pencil material, you can adjust the resistance over a suprisingly wide range.

When I said this was the best method I found, that doesn't mean it was all that good. The biggest problem is these resistors would drift a large amount. Just a tiny touch to the pencil trace could change the resistance significantly. I don't see this working out well for a potentiometer because something would always be rubbing against the trace. Nowadays there are conductive paints and epoxys, but these are expensive. You can probably make a sortof reasonable pot with some effort, but it won't compete in quality and cost with a commercial pot, even if you value your time at 0.

Making low value pots shouldn't be too hard because you can use something that conducts reliably, like a piece of wire or coiled wire to get more resistance. Anything more than a Ohm or a few Ohms will be more difficult.

One time I made a potentiometer that worked very well, but the purpose wasn't to save money or because real pots were inaccessible, it was to get a voltage-controlled pot. I did this with two LEDs and two CdS photoresistors. The result is rather non-linear, but it worked well enough for my purpose, which was to be able to regulate the amplitude of a oscillator that inherently varied with frequency.

So go ahead and experiment for the fun and learning of it. But, don't kid yourself that you'll be able to make anything as accurate, reliable, and scratch-free as a commercial pot for the same cost.

Answer 3

Automotive ignition wires. The graphite core should yield somewhere around 10000 ohms per foot, and they are nice and flexible. You might be able to find some used ones free. It shouldn't take much effort to peel off the rubber insulation.