PSN-L Email List Message

Subject: Re: BasicStamp question
From: Ed Thelen ethelen@........
Date: Thu, 15 Feb 2001 23:02:16 -0800

Steve Hammond wrote:
> Has anybody incorporated a BasicStamp micro in the 
> construction of their seismograph, tools, amplifiers, 
> or A/D?
> Regards, Steve Hammond -- PSN Aptos, California

About 10 years ago I got tired of re-leveling a 
garden-gate type seismograph (a one vertical post "Lehman")
that was more stable than its base.  (A machine adjusted
to 20 second period on a house slab needs daily
re-leveling in changeable weather.)

I used the BasicStamp to:
  a) send a re-leveling indication to the ADC
  b) short the sense coil
  c) turn on 2 infra-red LEDs used to help sense the pendulum position
  d) sense the relative outputs of two infra-red photo cells
      using an RC circuit BasicStamp AtoD recommended at the time
  e) operate a highly geared down stepping motor to
      move the leveling more toward nominal pendulum position
  f) undo c) above, then b), then a)
  g) go back to sleep for a day

Results of the experiment.
  a) BasicStamp ALMOST had the drive to operate the
     stepping motor reliably - had to go to higher current
     drive to gain 100% drive reliability
  b) photo sensing using the old recommended BasicStamp
     circuit is a bitch !!
       - temperature sensitivity
       - sensitivity to ambient light
       - sensitivity to everything
     even using differential circuitry did not yield
     the kind of reliability and stability and 
     demonstratability that I wanted.

Then I discovered the Internet,
and my interests changed.

If I were going to do it again -
  a) more conventional AtoD than offered
      by the old BasicStamp - like a real amplifier
      and a real ADC (or a more modern BasicStamp?)
  b) pay more attention to the optics so that I
      can show the thing working to my friends
      in normal light.
  c) tap into the data from a professionally 
     operated machine installed in a quiet location
     (2000 miles from a sea coast OR install a
      0.2 to 0.1 Hertz notch filter).
  Ed Thelen - Fremont, CA  ethelen@........

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Larry Cochrane <cochrane@..............>