It is obvious you are more into the fine details of
physics/math than I.

I do like your photocell idea.

I am simply searching high tech alternatives which
may currently be in existence but which no one speaks about
either due to proprietary laws or whatever.

If finding such a thing you might make or use a sensor
easily which is already out there but used for
other purposes.

Like take something from the world of amateur astronomy
and apply it to the world of US here.

It is kind of like knowing that the science of THAT
can also be applied and used within the science of THIS.
But it has never been tried before.

It may create a better WIDGET than any amateur has used or built before.

I may not understand the physics like you do,
But I do know the general idea of what I am seeking.

It may already be cheaply out there, we just don't know of it
due to forces trying to keep a technological secret.

It is wrong for the spy world to destroy human imagination
by spreading ancient technology to developing nations.
It is an insult to human intelligence.
But i seem to see such a thing happening even within this group.
We could all benefit as amateurs if human imagination were
allowed to be free. Developing technologies alien to
that which we are familiar.

Is it possible to get some electronics firm to dedicate
a bit of R&D to developing a decent new seismic sensor
to be used by Amateurs ?
Like Texas Instruments or Advanced Micro Devices or Motorola ?
Maybe the three could have a contest amongst its Engineers/Scientists ?
Create something no individual can do him/herself.

Regards,
geoff







On 3/28/2013 8:40 PM, chrisatupw@....... wrote:
> From: Brett Nordgren 
> To: psnlist 
> Sent: Wed, 27 Mar 2013 12:29
> Subject: Re: Seismic Sensors
>
> Hi Geoff,
>
>    The amplitude of Microseisms may be from ~0.5 micron to a maybe
> 20 microns. For Earthquakes, you may want to measure movements
> of ~10 nano metres upwards.
>     The size of the pixels in a good photo detector maybe ~10 microns
> minimum. This is a 'difficult / expensive technique' for trying to 
> measure
> earthquake signals. You may require costly optical components.
>    But you can use a couple of BPW34 photocells (87 cents each) for
> measuring movements down to ~10 nano metres OK, with a movement
> range of ~+/-1mm.
>    This is both cheap and quite easy to do. Have a look at
> http://jclahr.com/science/psn/chapman/photo_detect/index.html
> A good free filter design program is FilterPro from Texas Instruments
>    Regards,
>    Chris Chapman
>
> The only problem I can see is that the sensitivity you typically find
> in a good instrument may be somewhat higher than what you are
> considering.  For example, with the FBV instruments being operated by
> Dave Nelson, a 2 Hz sinusoidal ground motion which registers 10
> counts peak-peak on Larry's A/D would represent a ground motion of
> ~8nm p-p or about 18x the 0.44nm diameter of a large atom
> (Potassium).  So one A/D count at 2Hz represents a motion of about
> 1.8x an atomic diameter.  And most seismic observatories using 24-bit
> A/Ds are about 5x more sensitive.
>
> For a really good instrument, one needs to be thinking in terms of
> devices which can detect very small motions, though, in practice, an
> instrument's true sensitivity will be determined by its internal
> noise, not simply its bit-resolution.
>
> Regards,
> Brett
>
> At 06:47 PM 3/26/2013, you wrote:
>> On 26/03/13 23:56, Geoff wrote:
>>> I like the idea of using a WEBcam or something to look at the red dot
>>> then use a custom program to read the video and turn the graphic data
>>> into rectangular coordinates of a standard four quadrant graph
>>> with the point resting in the center of the graph
>>> But to do this in near real time may not be possible for myself to do.
>>> The max rate will be like 30Hz to 60Hz which is a video frame rate.
>>> Video is usually encoded and needs to be uncompressed.
>>> Uncompressing video takes lots of time to do so like a
>>> series of BMP captures at whatever rate would be the thing to do.
>>> You would take screenies at like 30 per second in a modulo fashion
>>> then save all after an alarm and the series of like
>>> 108000 BMP images would be decoded into a series of (X,Y) coordinates
> ??
>>
>> This sounds a bit like a modified optical mouse.
>
>
>
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