> From:    David russel 
> Date:    Sun, 29 Apr 2001 07:38:50 -0700
> 
> Does anyone, or rather has anyone done any experimenting with the Analog
> Devices ADXL-202 accelerometer ? If so any luck ?

I am working on single board systems using the ADXL202 and 
ADXL105 accelerometers.  Here are some links I have collected
on programming and soldering these surface mount chips:
http://www.infiltec.com/seismo/#links

The good news about the ADXL202 is that it is 2 axis and 
it can be interfaced to a microprocessor counter to read it
out.  The bad news is that its noise spec is the same as
the old ADXL05 chip that Larry Cochrane showed to
be too noisy for most seismic work.  My experiments
with the ADXL202 show noise levels similar to Larry's.
http://psn.quake.net/strongmotion.html

If we could reduce the ADXL noise level by ~10x then it would
be more like the Kinemetrics three component FBA-23A
commercial strong motion sensor that Larry compared
the ADXL05 to.  The newer ADXL105 has half the noise
level of the ADXL202, so that is a start.  I notice that Larry's
data spectra shows that most of the seismic signal he recorded
was below 5 Hz, so we could reduce the noise further by
by lowpassing the ADXL105 to ~5 Hz rather than the 10Hz LP
that Larry used.  I am working on an ADXL105 board that does
this.  It should have a noise level of ~ 0.5mg versus the
~1.6mg of Larry's ADXL05 system.  We will probably have to wait
for an improved accelerometer chip to get much lower noise.

To get some idea of what you might detect with an ADXL based
seismic system take a look at some the quake shake maps on the 
web. Here is a map of peak acceleration from a recent 5.1m quake.
http://www.trinet.org/shake/9627721/pga.html
If you click on the sensors located in LA (about 150km
away), they felt  ~0.15%g = ~1.5 mg.  That might be
just detectable with an ADXL system that had a noise
level of ~0.5mg.  

Since I am in quake impaired VA, I plan to send my
ADXL105 board to Jim ODonnell in NV to see how it
does against real quakes. 
   
Hope this helps,

Dave 
The Inexpensive Seismometer Project
http://www.infiltec.com/seismo/


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