Jim wrote:

> It depends on what exactly you want to record.

I want to record only local events, and I'd like to get as much useful 
data on these events as reasonably possible without spending thousands
on individual sensors. I guess the real question I have is this: what 
would be a good combination of sensors for this purpose? I am getting 
both the 1hz and 4.5hz geophones as per the group buy. This leaves me
one extra channel on the amp/filter board, so I am wondering which 
type of additional geophone would be good to add as a third? Then, in
addition to geophones, I am looking for other strong motion sensors 
that would be good for local recording, as a complement to the geos.

> Your geophones should be good for most local events up to the point 
> of felt shaking.

Okay, that is good, since I should detect the smaller local activity.

> The Analog Devices accelerometers overlap this a little bit and would 
> then be good up to the point of total destruction.

Well I think they are fine for me then. I understand that they will 
not be useful at all for teleseismic events, and therefore are not 
what most amateurs would want to use. But in my case they might be 
good for local activity (only during large events). Let's hope I 
don't get to the point of total destruction any time soon :)

Since I can get the ADXL202s and ADXL105s in the form of cheap and 
easy eval boards, I think I'll set up a few of them here, and work 
towards connecting them to a microcontroller with ethernet as I
described earlier. Analog also provides free samples so I already 
have some of these freebies on the way. If anything it should help 
me to learn about accelerometers, and sanity test the sensor <--> 
ethernet idea. It sure would be neat to have say 16 of these 
plugged directly into a 10-base-T hub, each with their own IP 
address and embedded web server. I could have one of my unix 
boxes run a cron job and grab the data logs. Also, I could use 
flash ROM on the microcontrollers to aid in saving data in the 
event of a complete power outage. One thing I like about the 
ADXL202 is that it has digital output, therefore requiring no A/D 
conversion, and easy to connect to a microcontroller or other host.

In the meantime I got some suggestions for sources other more 
sensitive accelerometers. Thanks everyone for all the help. This
stuff is very, very interesting.

  -- Doug 



 

   


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