The below is a forwarded reply to Raul (and all) on PSN email from David Lamb:
 
Raul; this is David.  Just have part of the amplifier design and tilt control
circuitry on paper.  Our designs keep changing with improvements. Just
recently got computerized thanks to Meredith.  Did not even have the time
set precisely on the SDR readout.  Computer time was set to a cheap
wall clock.  Could be a minute or two off.
 
The current working unit design of the SDR readout can fit in the palm of
your hand, as far as the magnets/iron structure for the magnets and the
graphite structure.  But; this design is soon to be replaced by a new design
that already has a 30 second (if undamped) oscillation period.
 
The amplifier consists of 3 very low noise op-amps.  The tilt control
circuitry is an additional op-amp.  The sensing optics uses special  heat
sink LEDs and gallium arsenide photodiodes from Hammamatsu, which
operate at a very low power for a quiesent, no noise, long life operation.
The low power of the LED has no thermal heating effect influences on
the optical flag of the 3 gram floating graphite structure.
 
So, this is the basis of the seismometer.
 
David Lamb