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Picture of This Seismometer is no toy!
This is an image of the computer recording "drum" that shows four events recorded on the same day at my station in Denver, CO; two in Mexico and two on the opposite side of the world in Sumatra. The vertical short-period instrument that recorded these events can be made in a home shop.

Smart phone "earthquake" apps that use the built-in screen-tilt accelerometers can only detect gross movements that can be felt. The seismometer in this Instructable can detect ground motion of less than 50 microns/sec. (a human hair is about 100 microns), way below what can be felt or seen. This makes it sensitive enough to detect earthquakes from anywhere in the world greater than magnitude 6.5 and much smaller for closer events. Yet, mechanical and electronic filtering limits local signal noise.
 
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Step 1: Comparison With Professional Instrument

Picture of Comparison With Professional Instrument
This instrument rivals those of the USGS Mobile Seismic Array if placed in a suitably quiet and environmentally stable location like a basement and you will be able to gather data in the background through a USB port using free software that requires very few cpu resources while performing other tasks on your computer.

Note that like the professional instrument it nicely differentiates between Primary and Secondary body waves as well as the larger surface (L) waves allowing distance to an event and even magnitude to be accurately measured.

Step 2: Seismometer (seismograph) System Components

Picture of Seismometer (seismograph) System Components
The seismometer consists of four basic components each of which I will describe in detail. The total cost will be between $300 and $350 U.S.. Free software to display and manipulate data is available online.

Step 3: Mechanical Component

Picture of Mechanical Component
This design is a vertical short-period unit that is tuned to wave frequencies of about 1 1/2  - 2 sec which gives strong response to the  P and S waves of an earthquake.
There is room for some design latitude, but the arm dimensions, spring slope and especially spring tension characteristics are critical.

Wood base and post are sufficient in relatively stable moisture conditions, but pores should be sealed with at least two coats of paint.
Aluminum can be used also, but presents its own thermal expansion issues. The metal must be non-magnetic.

Step 4: Overview of Mechanical Sensor

Picture of Overview of Mechanical Sensor
Major dimensions shown. Individual parts will be detailed in subsequent steps.

Step 5: Knife Edge

Picture of Knife Edge

A box cutter blade is used for the contact point of the arm "hinge". It fits into a piece of the aluminum arm material with a V-shaped notch that allows free motion of the arm up and down. The arm is made of 1 1/4 in (3.2cm) strap aluminum 1/8 in (.32cm) thick. The arm is aluminum and not steel because it must be non-magnetic so as not to generate a secondary magnetic field with the horseshoe magnet.

The post is held in place by wood glue and a large lag bolt inserted through a pilot hole from the bottom. The leveling screws will need to protrude through the bottom far enough for the lag bolt head to clear the floor.

Step 6: Springs

Picture of Springs
The spring parameters are CRITICAL. If they are too stiff the horseshoe magnet will not be heavy enough to lower the arm to horizontal without adding weights to the end of the arm. The springs below are what I used and are ideal. You will need three springs hooked end-to-end so you will need two packages.

I purchased these at Lowes Home Improvement in the U.S. Manufactured by The Hillman Group - Utility Extension Spring #208
Item #: 199346 |  Model #: 543004   $3.48 U.S.
http://www.lowes.com/pd_199346-37672-543004_0__?Ntt=199346&UserSearch=199346&productId=3115821&rpp=32

Adjust the arm to horizontal (using the bubble level) by adjusting where the upper spring hooks onto the fixed hook (see image in step 3).

Fasten the lower spring to the arm with a non-magnetic angle connector.

Step 7: Coil and Magnet

Picture of Coil and Magnet
I used a 30 lb. pull Alnico horseshoe magnet from ALL Magnetics Inc. Item # 07272. $35 U.S.
http://www.allmagnetics.com/hardware/horseshoe.htm
Fasten the magnet to the arm with a non-magnetic brass or aluminum machine bolt and nut.

The 2 3/4 in (7 cm) coil discs are 1/8 in. (3 mm) hardboard because it is non-magnetic. It needs to be quite stiff so as not to spread at the edges when the magnetic wire is wrapped.
http://www.dickblick.com/products/hardboard-panels/The spacer core of the spool is a 1in (2.54cm) wood dowel 7/16 in (1.1cm) long. It is important to get your magnet first and calculate how wide the spool can be so it provides a small clearance inside the magnet gap. Add wood dowel "washers" to the outsides of the to the spool to give it more strength (they are not protruding through the hardboard as part of the inner spool). Drill a hole through the dowel for a non-magnet machine bolt to keep the spool together against the outward pressure of the magnetic wire windings.

The magnet wire should be 26 or preferably 30 guage.
http://www.amazon.com/b?ie=UTF8&node=310354011

Drill a small hole through the spool core to the outside and feed a1 ft. (30.5cm) length through it to the outside. Alternatively you can tape the beginning end to the inside of the spool and let a 1 ft "tail" drape over the edge to the outside. Curl up the tail and tape it to the outside of the spool so as not to get it tangled and broken during the winding process. (You can see two ends coming from the coil). The wire is coated with lacquer so any final connections must be sanded.

After securing the spool with the bolt and nut, insert the end of the bolt into a drill press chuck and wind the wire from the purchased spool to the seismometer spool on the slowest speed. A hand drill can be used, but take care not to let the wire jump the spool and begin winding around the bolt. This can be tricky, but if you take your time and go slow there shouldn't be a problem.

Step 8: Magnetic Damper

Picture of Magnetic Damper
If the arm is set in motion without damping it would continue to move up and down for several seconds or even minutes. Since earthquake waves are in the 1 sec. to 25 sec. range, different arriving waveforms would be obscured by the arm's continued reaction to the initial wave. Therefore the arm must be dampened to return to its resting state rather quickly. This can be done with oil, but it is messy and viscosity varies with temperature.

The magnetic damper consists of a copper blade that moves through a strong magnetic field produced by 4 very powerful neodymium magnets. The blade and brass bolt are non-magnetic, but the housing IS MAGNETIC so the magnets can stick to it as are the spacer bolts and nuts.

Since the damper simply sits on the base so it can be moved in and out of the blade for adjustment, the housing must be heavy enough to prevent it from moving in the strong magnetic field produced by its interaction with the blade. You can buy 1/4 in 6.5mm) nickel-plated mild steel but I bought an inexpensive steel carpenter's square 2 ins (5.1cm) wide and cut it into six 2 3/4 in (7 cm) lengths with a hacksaw - three for each side of the housing. See the next step.

Step 9: Magnetic Damper Rear View

Picture of Magnetic Damper Rear View
I clamped all six pieces together and drilled the holes for the 1/4 in (6.5mm) bolts in 3 corners.
Neodymium magnets were purchases from K&J Magnetics, Inc.
http://www.kjmagnetics.com/

Four 1 in x 3/4 in x 1/4 in (Part No. BX0C4)  $5.63 U.S. ea.
They are arranged in opposite polarity on the same side and on facing sides.
S | N
N | S
Be careful with these rare earth magnets. They can raise a blood blister if you get skin caught between them.

The blade is made of 24 guage copper sheet. Heavier gauge can be used, but not lighter. It is 1 3/4 in (4.5 cm) long not including the shoulder and neck and 1 1/4 in (3.2 cm) wide. The blade can be soldered or glued into a notch in the bolt.
Clearance  for the blade should be about an 1/8 in (3 mm) on each side.

Step 10: Amplifier

Picture of Amplifier
I have tried several amplifier configurations for my seismometers, but the one below designed by Andy Loomis is by far the best.
It is very stable and features a commutating auto-zero (CAZ) op amp (Maxim MAX420CPA) which protects against low frequency noise resulting in baseline drift common in most other op amps. There are several online sources for the CAZ chip. They aren't cheap, but you will be making a mistake by going with a non-auto zero chip. TL082 JFET op amp can be purchased at Radio Shack 


You can see a detailed discussion of his amp and a slightly more complex version (Fig. 3.2) that I did not find necessary at
http://jclahr.com/science/psn/epics/reports/folded/

The time signal input terminal is optional and unnecessary when outputting to a pc as in my design. The connection from the 100k pot and the TL082  with the 68k resistor is still necessary.


Step 11: Amp Mockup

Picture of Amp Mockup
I created my amp on a solderless breadboard and stuck it to the bottom of a plastic project box. This setup is fine since the amp is going to be in an undisturbed location near the seismometer. In fact, it should be right next to the seismometer in any case. I added connectors to the back and the 100k pot as a panel pot to the front.

Step 12: Power Supply

Picture of Power Supply
The amplifier requires a regulated +12/-12v power supply. There are several designs you can find on the web and other options for this including two 6v lantern batteries. Here is the schematic for the power supply I used. Note that the PIN numbers on the positive and negative regulator chips are different. All of these parts can be purchased at RadioShack.

Step 13: Analog/Digital Converter

Picture of Analog/Digital Converter
I use the Dataq DI-158U Analog/Digital converter, but it is an obsolete model. It has12 bit resolution.
Both the DI-145 ($29) and DI-149 ($59) have 10 bit resolution (2^10 divisions = 1024 divisions over the +/- 10V input range which would give a 19.4 mV resolution over the 20V). This might produce some noticeable "stair-stepping" in the display trace and unwanted noise in the signal.

The DI-155 is pricy at $159 but it is >13 bit (2^13 divisions of the input voltage) and voltage programable. So at +/- 5V you would get 10V /8192 divisions = 1.2mV resolution, 16 times better than the less expensive models and will also produce less signal noise. Sampling rate doesn't much matter in low frequency earthquake data, but resolution does. It is up to you, but if you can afford it, go with the DI-155. Alternatively you could buy the DI-145 starter kit and see if you can live with the resolution.
Dataq website.
http://www.dataq.com/data-acquisition-starter-kits/data-acquisition-starter-kits.htm

Step 14: Software Options

Picture of Software Options
As mentioned above, you can use the Dataq Acquisition software that comes with the A/D converter kit. It will definitely collect seismic data, but there are programs dedicated specifically for seismic data collection, display, mainipulation, filtering and storage.

I use the free program called AmaSeis AS-1 developed by Alan Jones for IRIS.
I notice that he has not updated it to use the Dataq DI-149 A/D or the DI-155, but I am sure he would if he were contacted.
http://bingweb.binghamton.edu/~ajones/AmaSeis.html

It has recently been replaced by a Java-based program called JAmaSeis which is still in beta development. I haven't tried it yet and I don't know if it has all of the filtering capability as Alan Jones's original version. It is compatible with the DI-145 and DI-149 so far. I am sure they will be adding new A/D converters as requests come in.
http://www.iris.edu/hq/programs/education_and_outreach/software/jamaseis

Step 15: Cover the Instrument

Picture of Cover the Instrument
Your mechanical unit MUST BE COVERED and sealed against air currents which would create a great deal of signal noise.
I used part of a styrofoam insulation sheet taped at the four corners and used a heavy piece of particle board for the lid which holds the cover tightly to the floor.

Step 16: Magnetic Damper Adjustment

Picture of Magnetic Damper Adjustment
Once you are getting a signal display on your screen it is time for the "lift" test to adjust the magnetic damper.
Cut out a small piece of file card 1/2in x 3/4in (1.3cm x 2cm) and attach it to a thread or fine string about 1 meter long and attached the other end of the thread to a stick or dowel of equal length.

Open the lid of the unit cover and lower the file card cutout onto the arm just behind (closer to the post) the damper attachment bolt. Make sure the string does not tangle in the spring. Drape the string over the edge of the box and close the lid. Stand quietly for a minute or two to let it settle down. Then raise the stick or dowel suddenly so the card lifts off the arm without disturbing the box.

If the lift test looks like this image, then the arm is properly dampened. If the initial deflection goes up instead of down, reverse the leads from your unit to the amplifier. If the deflection:rebound ratio is between 12:1 and 15:1, it is properly dampened.

If the ratio is less than 12:1 move the damping housing with the magnets to cover more of the blade. If the ratio is greater than 15:1 or if there is no rebound, move the damping housing back to cover less of the blade. Damping can also be controlled by changing the distance between the copper blade and the neodymium magnets.

Step 17: The Moment of Truth

Picture of The Moment of Truth
Once you have adjusted the unit's damping you are ready to troll for earthquakes.
Be patient, it may take several days to a week or more for you to record your first earthquake. It takes one close enough or large enough if it is far away to move the floor literally a hair's bredth.  Depending on where you live you can expect a event every 3 to 10 days on average. More often if you live on a tectonic plate boundary.
Maybe you will get lucky and record the "Big One" like I did with the Great 9.0 magnitude Japan earthquake March 11, 2011 that caused a devastating tsunami. I recorded waves from this earthquake for more than four hours. The earth rang like a bell.

Good Luck and Good Hunting!
joaniehook6 days ago

Anyone out there using Linux Distributions for the software for this unit? I am currently running Linux Ubuntu 14.04LTS and intend to stay with it.

hi is there any way to don't make the amp or buy it because I don't know how to make the amp and why we should use amp in this device

Alderin10 months ago

Very cool stuff. I'm also of the opinion that an Arduino could make
some improvements on the electronics side of the project. Capable of
low-power long-term logging to an SD card, and A/D up to 10 bits without much expensive hardware (other than the amplifier). A/D converter modules aren't too expensive to increase the resolution, I found a 24bit dual-channel A/D module on ebay for $6 US.

The Arduino software for datalogging to an SD card is already everywhere. I might even add a "run-length-encoding" compression to allow the log to cover longer periods. Could be done, might lower cost a lot. I'll have to do more digging.

And just for clarification, your pickup coil is 1 3/4" thick from outer edge to spool core? How much magnet wire is that?

barkergk (author)  Alderin10 months ago

Thanks Alderin. I don't really have experience with arduino, but there is no reason why it won't work. I would avoid 10 bit resolution and keep in mind that any design needs to have a low pass filter and should have a comutating auto zero (CAZ) function (see step 13). There is a link to magnet wire in step 7. Item 9 on that list should do the job (30 gauge, 1606 ft.)

auschwitz1 year ago

will the a/d converter work on windows 8 or 8.1?

barkergk (author)  auschwitz12 months ago

I don't know but I don't see why not. It is read through a USB port. Go to DataQ's website and see what you can find out.

http://www.dataq.com/

barkergk (author) 2 years ago
Here is a "Great" Earthquake I just recorded on 2013-05-23 using the seismometer described in this Instructable
Mag. 8.3 Sea of Okhotsk SW of Esso Russia.
54.874°N 153.280°E depth = 608.9km (378.4mi)
EQ 8.2.JPG
Shreddi2 years ago
That is so cool. Thanks for sharing. Man, you have some patience. Great Job. thanks again.
JTomM1292 years ago
Nice 'ible. Looks a lot like a Scientific American project from about 1957 but of course back then no A/D converters or USB interface. It would be nice to use Aduino with a TCP/IP net sheild and get remote data downloads so you coul put this way away from man made activity. My $0.02 worth.
barkergk (author)  JTomM1292 years ago
Re: Scientific American Article, see my exchange with joen below. I would love to see someone (you?) give the Aduino idea a try.
panic mode2 years ago
this is one amazing instructable, an example how project should be documented. don't hink i will build one soon but still must thank you...
barkergk (author) 2 years ago
Below is an extra Instructable 3 month Pro membership.
First come, first serve.
redeem it here: http://www.instructables.com/go/pro?code=involved11rocky
Your gift code: involved11rocky
baudeagle2 years ago
Do you record any false readings from large trucks, mowing the lawn or just walking about the house?
barkergk (author)  baudeagle2 years ago
The raw data can be filtered on three levels.
The mechanical unit itself is tuned to relatively low frequency waves, the electronics have built-in filtering and the software can further filter the digital data. Having said that, it is best to have the unit in a quiet, thermally stable location at least six feet away from any foot traffic. Road traffic does not seem to be a significant issue. You are always going to get some "microseisms", but these are usually caused by the normal moans and groans of the earth, strong winds and even ocean storms causing large wave crashes on the coastline believe it or not.
joen2 years ago
Is the magnet holder for the magnetic damper attached to the base in any way or is it just sitting there the base unattached? This instructable reminds me of a column that appeared many years ago in Scientific American magazine called "The Amateur Scientist" where Martin Gardner presented many science projects like this in various fields of science.
Well done!
barkergk (author)  joen2 years ago
Yep! Good memory. The Scientific America Article featured Jim Lehman's horizontal long-period design in 1981 which I made and it is still running.
The magnetic damper just sits on the base so that it can be moved in and out of the blade easily for damping adjustment.
joen barkergk2 years ago
Well... maybe my memory isn't so good after all. Martin Gardner wrote the column "Mathematical Games" for Scientific American. "The Amateur Scientist" was written by several writers including C. L. Stong, Jearl Walker and others. I remember the article you mentioned which prompted my comment. Wow! Your original setup is still running 30+ years later! Have you had to redo or repair worn parts or electronics? Wonder if this one will last another 30+ years.
barkergk (author)  joen2 years ago
I ran the Lehman seismometer at my school for my students for 25 years. We recorded hundreds of events including the Loma Prieta (World Series) earthquake.
I made sure that my students were well versed in seismology. A seismogram is worth a thousand words :)
kelseymh2 years ago
What an outstanding project! Like all good instruments, you have to spend some amount of money on it, but I am really impressed at how inexpensive it is. There's a part that I think I must have missed, though. How do you calibrate the amplitude?

One minor criticism -- you refer to "acceleration" of 50 um/s. Either you meant "ground motion" or "velocity", or you missed out a "2" on your units.
barkergk (author)  kelseymh2 years ago
Amplitude calibration can be done using the AS-1 software with the data from the lift test if you know the mass of the filecard cutout and the distance from the hinge when it is lifted off the arm. A more practical way to do it is to graph the p-wave amplitude of your trace against the reported magnitude of the earthquake. There are a lot of variables in extracting magnitude from a single seismometer. The USGS collects data from hundreds of seismometers and feeds it into a super computer at the Earthquake Information Center on the Campus of the Colorado School of Mines in Golden, Co.
Regarding your acceleration correction, you are of course correct and I will update the page. Thanks for your input. Always appreciated.
Ah, thank you! That first sentence answered my question. The lift test, with a known load, gives you the vertical scale.

Of course, you can't properly get an earthquake magnitude out of a single seismometer trace, unless you just happen to have been sitting at the epicenter (and your collapsing house didn't break the instrument :-). You need to know the distance to the hypocenter, you need to know something about the different formations the waves traversed, and so on.

With a sufficently large number of stations, over a large enough area, you can not only solve for the magnitude, but you can even invert the transport problem and derive the internal structure of the Earth from the pattern of signals.

(Yes, it's clear you already know that stuff! I'm writing for the same reason you did -- for the benefit of anyone else reading this.)
barkergk (author)  kelseymh2 years ago
Thanks kelseymh. Yes seismic tomography I think it is called. As you probably know, moment magnitude is used today which is based on the seismic moment, a function of the surface area of the slippage interface, the distance it slips and the rigidity of the rock involved. I also have a horizontal long-period unit running simultaneously that gives me two legs of an x,y,z monitoring station that would allow me to not only determine distance, but direction as well. Sigh! So little time, so much to do.
flavrt2 years ago
Outstanding project. I need this to monitor my neighbors' activities.
Kiteman2 years ago
I always love real science projects.