Electronic Inks!

[cjdelphi]

Website sells these low resistive pens along with resistive pens, looks pretty neat eg building circuits on the bus/plane/train or just prototyping stuff quickly

The pens are a little on the expensive side though around $13 - $20 range but looks like a lot of fun!

 

[wingnut]

I think the pens look a whole lot of educational fun.

It inspired me to pull out a pencil and draw 3 resistors in series on a piece of paper, (in thick pencil lines) and 3 resistors in parallel, put an ohmmeter across these, and the graphite acts as a resistor and so the resistance of resistors in parallel drops, while the resistance of resistors in series rises.

Next time I have to teach electricity, I will get the students to draw the resistors in thick pencil in their books, and measure the resistance of our graphite resistors. Graphite has high resistance in such a thin layer, so set the multimeter to mega-ohms .

 

[BobK]

And you can draw capacitors if you use both sides of the paper!

Bob

 

[cjdelphi]

With the pencil i used it to create a variable resistor for an LED, by moving a wire up and down the lead track..

However it was dim, so i connected the other end of the track to the base of a transistor or at least i think i did (tried many years ago) so i might have just dreamed up the transistor but it should work

 

[wingnut]

With the pencil i used it to create a variable resistor for an LED, by moving a wire up and down the lead track..

However it was dim, so i connected the other end of the track to the base of a transistor or at least i think i did (tried many years ago) so i might have just dreamed up the transistor but it should work

With a BC547 NPN transistor and 1K on the base, a LED connected to the collector via a 150 ohm resistor will light up even if one has 6 inches of graphite track.

So with pencil graphite we have variable resistors (cjdelphi), a capacitor using Bob's suggestion, conductors, switches (if one folds the paper over. And for teaching just add a transistor with a LED and they can see the resistance change from the brightness of the diode. I just wish there was some kind of conductive glue to stick the transistor to the graphite tracks. I did try stapling the leads to the graphite tracks, but it does not make contact.

One does not even need a transistor. Just use one LED with no resistor since the graphite acts as a resistor, and the brightness of the LED will show the varying resistance with the varying length of the tracks.