Introduction: Make a Pencil's Lead Potentiometer (Experimentations)

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Here is a really simple experiment in witch you will make a Kind of potentiometer (Variable Resistor) out of a sheet of paper and a graphite pencil (Lead Pencil)... Impossible you think? Check it out!

So first , What is a Potentiometer?
Its not very complicated, to make it short, it's a kind of resistors ( Limit the current flow) but its adjustable, so you can raise or lower the limit of the current flow.

I recently seen a video of MAKE Magazine (MAKE : Present The Resistor) on Youtube in witch they were doing something similar to this and thats where I got the idea to make an Instructables about how to make this simple Variable Resistor.So I have no credit for the idea, I just did an Instructables, to share it with you!

The Idea is to draw a band (with a Graphite pencil) on a sheet of paper ,the band of graphite will act as the Variable Resistor (Potentiometer) because the graphite conduct electricity but poorly.

Step 1: Material

Here is what you will need to do your simple Variable Resistor and to test it:

Variable Resistor:
  • Sheet of paper
  • Pencil [You need a very soft one like 2B+ (Less may not work properly)]

To Test the Variable Resistor:
  • Multi-Meter
  • an LED
  • Alligator clips (2)
  • Source of power (9v battery is good)

Step 2: Draw the Variable Resistor

On the sheet of paper , you will need to draw a band about a centimetre wide and 5cm long and full it up with Graphite pencil. ( You can also try with longer band! ).

Step 3: Testing With the Multi-Meter

To test your Variable Resistor with a Multi-Meter, you need to set it to the Ohm section(To test the resistance of the Graphite pencil), It work well with 2000k and anything in K.Put one electrode on each extremity of the band and look the resistance on your Multi-Meter, then get the electrode closer and closer and see what happen... Check the video!

Step 4: Testing With LED - Assembly

You can also test the Variable Resistor with an LED. Here is how to do it: First connect your 2 alligator clips to the 9V (one on each pole), then connect the Negative clip to the negative lead of the LED, and finally, bend the positive lead of the LED(Anode, the longest) so its easy to move on the paper and it gives good contact. ( If you don't have any alligator clips, you can replace them by normal wire, simply twist around the components to make the contact, or solder ) *Tips : If you don't know witch lead of the LED is - or + , test out with a button cell !

Step 5: Testing With LED - the Test

Now that you have your assembly, touch one end of the band with the other alligator clip and the LED lead on the other end of the band and slowly make the 2 connection closer and closer, see what happen... (*IMPORTANT* Avoid touching the LED lead directly on the battery pole or you can burn it up! You can also add a resistor in the circuit to avoid any damage of this kind) Check the Video! I made the Video a bit darker so can so the LED glowing! Explanation: The reason why the LED is glowing is because the current from the Positive pole of the battery ( Black clip) flow through the Lead or Graphite band and complete the circuit to the LED, result; the LED is glowing. Now the reason why the LED get brighter when you get the black clip nearest is because the Lead have some resistance [(Doesn't conduct electricity perfectly)(Measured in Ohm)]. So the closer you get to the LED, the less resistance the Lead provide you so more current go to the LED and make it brighter!

Step 6: Experiments!

Try wider or longer lead band or try other patterns and see what happen..! Try with other conductors like metals or anything else you know! Try with other kind of pencil (2H, 2B...) Try colouring lighter or darker for different result! Experiment, Experiment, Experiment ! and have some fun!!

Hope you enjoy !