Hi Ted,

I'm curious how your recording is going?  Did you catch the M 9 Sumatra event?

I'm working with some students that the Colorado School of Mines who are 
interested
in photo detection.  Would you be willing to share your electronic circuit 
with them?

I've been recommending using one light source and two detectors arranged so 
that
when a flag is centered, both sensors are equally illuminated.  Any 
movement increases
the light to one and decreases it to the other.  Since the output of 
interest is the difference
between the two sensors, slight variations in the brightness of the light 
will not cause
a false signal.

Cheers,
John


At 03:52 PM 4/7/2004, you wrote:
>Hi
>
>John has kindly posted my attempt at a 'mini horizontal' seismograph, if you
>are interested please go to:
>
>                      http://jclahr.com/science/psn/rogers/
>
>I would be grateful for an comments or improvements you may think I might
>incorporate in the unit, especially in the area of feed back to the light
>source.
>
>Regards
>
>Ted Rogers
>
>
>
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