-1-     The Seismographic sensor.

 The seismographic sensor consists of
 a geophone and an analog to digital
 converter.

 The geophone continuously generates
 analog data by picking up vibrations
 from the surface it is mounted on. The
 vibrations are transformed into
 an analog electric signal.

 The analog signal can be digitized
 by the sensor's A/D converter.

 -2-     The A/D converter.

 The analog signal generated by the
 geophone needs to be converted
 to a stream of digital data so it can
 used and processed by a computer.

 This is done by using a so called
 Analog to Digital converter.

 This converter digitizes the signal
 to a BCD (Binary Coded Decimal)
 value and buffers the digitized data.

 The binary data can now be accessed
 and read from the sensor with a computer. 

 -3-    The Data Logger.

 The data logger is a computer that is
 connected to a sensor and logs the data.

 The seismograph's data logger also controls
 the sensor and sends commands to the A/D
 converter to continuously check and validate  
 the data that was digitized.

 The logger timestamps the raw data and
 stores it locally.

 The last 2 minutes of data are formatted
 and via a network connection stored in a
 database server for easier access.

 The logger continously retrieves data
 from the sensor and adds some extra
 information that shows the sensor status
 at the moment the data was retrieved.

 -4-    The Campus Network.

 All computers that are used for
 retrieving, processing and displaying
 the seismic data from the sensor are
 connected to the DePauw campus
 network.

 The computers involved are:
 - a data logger.
 - a database server.
 - a web server.
 - the Geosciences kiosk.

 The data logger and the sensor can be
 located anywhere on the Internet.

 -5-    The Database.

 The last 2 minutes of data retrieved by the
 data logger are stored in a simple via the
 web accessible database.

 Not all data is permanently stored in this
 database since a lot of data is so called
 back ground noise. All the raw data is stored  
 in a different location in a more efficient
 and more compact data format.

 The data stored on this database server is
 used by web based Java applications that
 display it in a browser window.

 -6-    The Web Server.

 The seismic data is displayed with web based
 applications on the World Wide Web.

 Special applications (in Java) are developed to display  
 the continuous stream of data in a browser window.

 The webpages of this seismograph can be accessed
 by anyone from anywhere on the internet.

 The Geosciences seismograph kiosk accesses the data
 via the web also, however it does use software that is
 custom built for the kiosk.

 -7-    The Geosciences Kiosk.

 The Geosciences department's kiosk where the seismic
 data is displayed is a 42" plasma monitor that shows a
 seismograph drum written in Java running in a web page.

 The computer for the kiosk is a custom built embedded
 system that only uses 20 Watts. (a typical desktop
 computer uses approximately 350 Watts). The plasma
 display is switched to a power saving mode by the
 computer during the late evening and night.

 The kiosk displays details of recent seismic events and
 also plots these events on two maps.

 Visit the kiosk on the 2nd floor of the Julian Science Center
 near the Geosciences suite's main entrance or click on the
 image (your mouse pointer is on it) to visit the online version.  

 The Java Runtime Environment (JRE) plug-in  
 needs to be installed to view the online kiosk

 -8-    The Internet.

 The DePauw campus network is connected
 to the Internet and the online version of the 
 kiosk is accessible via the World Wide Web.