On 7/18/2013 5:34 AM, Ravi wrote:
> Hello all,
>
> Is there any method to detect an oncoming train about 2 KMs away?
>
I found a method that works but it requires a bit of DIY.
Parts:
  1/4 inch PVC pipe 3 inches long
IR LED
IR photo-transistor
opamp of your choosing, 741 , 324 will work

Put the IR led in the PVC pipe and attach the photo-transistor pointing=20
in the same direction as the IR led, but on the outside of the pipe.=20
Point both at the surface of a liquid in a shallow container and put=20
that container on the ground, or slightly below it.  Needs to be in=20
light tight enclosure.

Whenever there is even slight vibrations in the earth a wave pattern=20
will appear on the surface of the liquid. The IR sensor will pick up the=20
reflections from the wave pattern on the liquid , amplify that with the=20
opamp.

I stumbled upon this while working with optical liquid level sensing and=20
noticing a lot of noise in the results whenever the train passed through=20
the area  miles away. The wave pattern may not be obvious to your eyes=20
but look at it on a scope and it is very good at picking up seismic stuff.

You an use vegetable oil or water or whatever suits your situation best=20
for the liquid.
I didn't experiment enough to determine what would be the optimum size=20
for the liquid in the container surface area, I would guess the larger=20
the diameter the more sensitive it could be.

Think Jurassic Park and the coffee cup in the vehicle scene.

Mark



--=20
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