A Precision Crystal Detector

copyright © 2006 by Larry J Solomon


I wanted to have a way of experimenting with various rock crystals used as radio signal detectors. The usual crystal set detector was insufficient for my purposes, so I set out to design and make one that could be precision guided to any spot on a crystal with microscopic accuracy.  This picture shows the final result.

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This detector uses a "microscope stage" that I purchased from Edmund Scientifics. A brass plate serves as an electrical contact under the crystal. The "needle" is just a copper wire soldered to a brass ball (a lamp part found at Lowe's). Other materials include a varnished padouk wood base and small fashioned curved piece to hold the rock in place (epoxied to microscope retaining lever), an alumininum rod, a fashioned lucite extension, and a small fluted wood dowel. The microscope stage does most of the work. When a crystal or rock is placed on the brass plate it must make electrical contact -- if this does not occur automatically, an alligator clip probe can be attached to the crystal and base.  The brass plate has a wire lead hidden under the board for connections. The two black knobs move the crystal under the needle in precision, measured increments along the two axes (up-down, left-right). The needle acts as a gravity activated detector. A hole is drilled through the wood dowel so that the detector wire slips easliy through it. It falls on the crystal and maintains contact with it when the crystal is moved. A small alligator lead may be clipped just below the brass ball for connection. A more elegant solution would be to create a small mercury well inside the dowel through which the detector wire travels and an outlet wire connects through the lucite arm.

Here is a picture of the detector in operation with a molybdenite crystal.


The wingnut allows the raising and lowering of the arm to accomodate most heights needed. One can see from this that most shapes and sizes of crystals can be accomodated, and the detector wire moves smoothly in contact with the crystal.  I use pieces of a standard "soft vinyl eraser"  to take up slack, and this helps hold the crystal in position. Any small pieces of rubber would work as well.


The performance of this crystal detector is excellent, and one can return to any spot found on the crystal with some precision.