As a second seismometer, I chose to build a vertical seismometer. One of the simplest designs is that of the AS-1 vertical seismometer as sold by The Amateur Seismologist.
I copied the design of Dewayne Hill’s Homebrew Vertical and the metal parts were ordered Online Metals and I think that the total price of the seismometer came to ~$100 (not including the electronics)
Here are some pictures.
As an aside, I really think that one of the coolest things in the world is the eddy effect that aluminum and copper display when in the presence of a magnetic field. I had a long aluminum strip that I slid down through the interspace of the magnets, and it just was like it was flowing through molasses.
Please note, if you duplicate the above, make sure that you measure the vane size TWICE. I ordered it pre-cut and neglected to include the top tab.
The sensing coil was purchased from Larry Cochrane for $20 and has a 6′ RCA cable soldered to it.
The Lowe’s around me has a ready supply of the springs. Some have said that it needs to be cut. In actuality, I left mine full size and just added some weight at the end.
(Update – 2012) – The AS-1 is now offline. Like my Lehman design, I will be donating it to a local college so that future geologists may benefit to some small degree from my work.