Instructables

Make a Pencil's Lead Potentiometer (Experimentations)

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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!

 
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dava_24 years ago
Nice, Very Nice!
catfish234 years ago
 Excellent project, i will try it with some spare electronics parts.
chosenone35 years ago
I've done almost same thing with white glue and the thing from batteries (black stuff) when it dries it has good resistance and when you apply water it becomes flexible ;]
Patented (author)  chosenone35 years ago
Heh?
well its almost the same thing it acts as a resistor but you have to play with amounts of "charcoal"(?)  and white glue to get desired results.

Patented (author)  chosenone35 years ago
Oh ok I get it!
But its not dangerous this black charcoal thing inside the batteries  ?
I don't think it is but if it is you can use activated charcoal I think.
xitis5 years ago
doesn't work with me...
Patented (author)  xitis5 years ago
Are you sure your LED is working? did you try to switch the lead polarity on the battery? Check it out and send me back the result !
xitis Patented5 years ago
the LED is working fine...i tried it on direct lead and it is working but somehow it is not working on paper...
Patented (author)  xitis5 years ago
Ok than whats the pencil your using?
Patented (author)  Patented5 years ago
And are you sure you put enough graphite on the sheet( it need to be very dark , work better with the pencil i mention.
raniamit1105 years ago
Cool!
CelticLock5 years ago
Very cool project!