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  • Author Author: jc2048
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The Gold of the Fool and the Whiskers of the Cat

jc2048

Back in February, I visited one of the small museums that exist in the town where I

live. It's a natural history museum and is based in an old church. It's a lovely

place to visit, with lots of curious things to look at. In the shop, on the way out,

there was a basket with small chunks of rocks and minerals for sale and I bought a

small piece of 'fool's gold' (iron pyrites); I figured that an old fool like me

deserved a piece of gold to treasure.

 

image

 

What I didn't know back then and have only just discovered is that iron pyrites is

a semiconductor (thank you, Wikipedia!) and in the old days was sometimes used as

the 'crystal' in a point-contact diode (for demodulating radio signals in a crystal

set).

 

Well, I thought, that deserves an experiment. So here is my attempt to make a

point-contact diode, and it turned out to be surprisingly easy. I simply broke one

of the small cubes away and held it in one clip of a 'helping hand' contraption.

 

image

 

That clip I connected to the ground of a signal generator. The drive from the

generator I fed through a 10k resistor to a piece of wire-wrap wire which I arranged

to scrape across the surface of the cube. My scope then measured the output from my

improvised diode.

 

image

 

A little movement of the wire and I soon found a spot that rectified nicely [I was just

so surprised - I really didn't think that this was going to work].

 

image

 

The forward voltage looks to be a little over a volt. That's much higher than a

silicon metal-junction diode (a Schottky diode).

 

And that's it. No need to melt silica in an oven and grow it into a crystal with

99.99-whatever % purity. Instead, an instant semiconductor straight from nature.

 

Do I get a cat badge for this foolishness?

Parents

  • I love this kind of off the cuff experimentation. Pretty cool. One of my scout manuals had instructions for making a crystal set ( back in the 1950s). The crystal was perhaps a piece of pyrite I am not sure. I made the cat's whisker out of a bent safety pin. The capacitor was tin foil and wax paper and the coil was enameled wire wound on a paper tube. After I wound the coil I used sandpaper to sand off an area of enamel and built a wiper to slide over the bare wire to produce a variable inductor. Thankfully there was a fairly powerful AM station in the area and the thing worked. I am not sure that it worked because it was functional or just because there was enough field density in my area to pickup that station on ones tooth fillings.

    John

Comment

  • I love this kind of off the cuff experimentation. Pretty cool. One of my scout manuals had instructions for making a crystal set ( back in the 1950s). The crystal was perhaps a piece of pyrite I am not sure. I made the cat's whisker out of a bent safety pin. The capacitor was tin foil and wax paper and the coil was enameled wire wound on a paper tube. After I wound the coil I used sandpaper to sand off an area of enamel and built a wiper to slide over the bare wire to produce a variable inductor. Thankfully there was a fairly powerful AM station in the area and the thing worked. I am not sure that it worked because it was functional or just because there was enough field density in my area to pickup that station on ones tooth fillings.

    John

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