-1-     The Seismographic sensor.

 The seismographic sensor consists of
 a geophone and an AD converter (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 then is 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 (A/D) 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 wireless connection stored in a
 MySQL 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 Wifi Link.

 The data logger and sensor are somewhat
 remotely located, and are connected to the
 LAN via a dedicated wireless link.

 -5-    The Local Network.

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

 The computers involved are:
 - a data logger.
 - a database server.
 - a web server.
 - a display or kiosk.
 - a PC, laptop or other device.

 The data logger and the sensor can be  
 located anywhere on the Internet
 separately from the DB server and
 from kiosk and other clients

 -6-    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 applications that
 display it in a browser window.

 -7-    The Web Server.

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

 Special applications 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.

 -8-    The Kiosk or Dedicated work station

 Data can be displayed on/in a kiosk, a large TV, or  
 just a work station or other device.

 -9-    The Internet.

 The local network is connected to
 the Internet and the online seismograph
 is accessible via the World Wide Web.