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No, sorry it's a three paddle C measurement. The middle paddle moves back and forth, relative to the two ends. The mica is just an insulator between the two outer paddles. Hey, spend some of Highlands profits and buy his book. I can almost guarantee that you'll enjoy it. (It?s the kind of read that you have to chew through slowly though.)

George H.

The Electronic Goldmine geophones (I bought one) are vertical types, a spring-loaded magnet in a coil.

Depends on amplifiers; generally, though wind noise (trees? Are you inside a building?) and road noise (or nearby herd critters) will be picked up.

Not clear if your mic input is good at the earth-movement frequencies which are circa 1 Hz. Pro equipment uses FM modulation into analog tape recorders (or, it did when Mt. St. Helens was acting up).

That means you need three axes of sensors; it'll cost ya. Horizontal sensors of the geophone type aren't a surplus item, to my knowledge.

There have been multiple articles in Scientific American, in the (late, lamented) Amateur Scientist column; check out April 1996 and Sept 1975 and July 1979. The collected columns are available on CD-ROM

An iPhone 3G with a cracked glass or a Motorola Droid A855 goes for $30-$60 on eBay. That's about half the budget. $1 for the software and you have a working seismograph. If you don't like the iPhone 3G with a cracked glass, put some cellophane tape over the glass. The 3G still works with a broken glass, unlike the new and improved iPhones and Androids. I'm not sure about the A855 as I've never seen one with a broken glass. Think of it as saving the smartphone from premature recycling.

$20 plus whatever the Arduino board costs. My guess is that with packaging, you'll blow the "under $100" budget.

Dunno. My uniformed wild guess is that the MEMS sensor is quite similar to the one in the various cell phones. I vaguely recall the

Googling: The largest earthquake forces that have been measured are about 1 to 2 g ...

Looks like the 2011 earthquake in Japan, magnitude 9.0, was only good for 2.99g (vector sum of 3 axes). Methinks more sensitivity than a commodity MEMS sensor will be needed.

Gone to vote for the losing candidates... It's a tough job, but someone has to do it.

I don't think you would want to detect movement, you would want to measure the changes in current required to keep it stable.

All you need is a sound meter that detects utterances such as, "What the f*** was that?!?!?!" That's what I said during the Long Island earthquake last year... almost knocked me out of my desk chair. (Since a commuter train goes right by the TLSI building I thought the train had jumped the tracks ;-) ...Jim Thompson

apparently it has four electro magnets inside controlling the hover I guess you could just hack into it and measure the currents

-Lasse

BG Micro has them for $39.95, or just the sensor for $22.20

RT Clark sells a 3 component (X,Y,vertical) for $135. Like I said in my other post, don't screw with the surplus junk. New doesn't cost that much more, and you get specs and support.

If the original poster wants to detect distant quakes, he is better off with a 4.5Hz model than a 10Hz natural frequency. The lower frequency geophones cost a bit more.

RT Clark sells new geophones on ebay, though I don't think they are any cheaper than just calling them up and ordering what you want.

All these geophones have spurious frequencies. That is something to take into account. That is why I really think buying surplus stuff like old geophones from mil surplus is the wrong way to go. They were used in intruder detection systems.

Use a dynamic mike..

On a sunny day (Tue, 06 Nov 2012 11:51:19 -0800) it happened Jeff Liebermann wrote in :

No, no As I pointed out, I wrote some soft to test it from the PC par port. If you happen to have a PC running 24/7 all you need is a connector, and wires, it gets powered from the parport too. Then you can have it log 24/7, for years. A plasic box is about 1 Euro here, cement it to a wall, so for less then

Well, of course I do not know if it is usable as earth quake detector, the other links to real detectors here are probably the real stuff, but to log via the PC is an interesting feature. I have not used Arduino ever, do not like it. something to do with C++ perhaps, you could use that 30$ other computah perhaps.

There was an article in 'Wireless World' many years ago describing a capacitance tiltmeter using mercury. Two containers of Hg joined with a long flexible pipe with plates which you could adjust to sit just above the Hg. Very sensitive.

There were also 'Mercury heave gauges' commercially available somewhat later for use in (vertical) ground movement monitoring, but I never saw one in real life.

As for the OP, what do you need? A geophone for local events at 10Hz or so, or a seismometer for global events at 10mHz or so? There's a big difference.

Cheers

Nuts & Volts magazine had a construction article a few months back:

Build the Poor Man?s Seismograph

( You'll need to click on the link. )

Available in kit form here for $85:

Enjoy...

Frank McKenney

$35 for an earthquake alarm. It has a one-bit digital output. 0 = no earthquake 1 = run for your life While the output may be insufficiently granular, it might be useful for confirming that the reason the building is collapsing around you was caused by a genuine earthquake, and not the result of foot stomping and head banging after last nights election results were broadcast.

More quake detectors:

A shelf full of wine bottles can do that.

The difficult part is finding the mercury. Fortunately, I have some: For a while, I was making ecologically incorrect mercury tilt switches for laptop theft alarms.

Take a look here:

The web site mangles the frames in Firefox. No frames works better:

Adding mass to any microphone, speaker, record player pickup,.. I like the higher impedance of the pickups.

Greg