Unlike laptops, desktops do not have accelerometers inside. So we connect
inexpensive universal serial bus (USB) accelerometers to
desktops. The USB sensors use a similar
accelerometer to the Sudden Motion Sensor that comes in Macintosh laptops. USB
accelerometers connected to desktops have several advantages over laptop
sensors
Desktops are not usually moved around as much as laptops.
Desktops are usually placed on the floor or on sturdy desks, but laptops are often on peoples laps.
Third, the USB accelerometer is physically separated from the keyboard, so typing does not effect the sensor and the USB sensors can be monitored continuously rather than when the computer is otherwise unused.
A USB sensor can be attached to any desktop with a USB port, not just certain ones.
The sensors can measure acceleration in three directions. The easiest way to think of these directions is as the 1) up/down 2) front/back, and 3) side to side motions bobbing motions of a boat. With these three components of direction, it is possible to find the direction of the acceleration. If your desktop is not level (or horizontal), the directional acceleration may not return a zero value when it really should. This is why our software zeros each directional acceleration before it begins to monitor the sensor.
Desktops connect to the Quake Catcher Network over the internet. Typically, when the QCN software is running, there isn't much need to transfer the data to our headquarters. Instead, the Desktop monitors the data localy for new high-energy signals and only sends a single time and a single significance measurement for high energy signals. If our server receives a bunch of these times and significance measurements all at once, then it is likely that an earthquake is happening. If the server receives only a time and significance measurement from one desktop, then the server knows the USB sensor was shaken by something smaller and more local (like your sister running by, or the door slamming).
Soon teachers will be able to request USB sensors for their classrooms. These are not yet available for the public. Once you have a USB sensor, you can download the software that will turn your computer into a Desktop whenever it is connected to the internet and you are not using it.
When installing the desktop software, please tell us where
the desktop is located (Address is okay, but exact latitude and longitude are
better). Otherwise, the sensor will be less useful. The easiest way to get the
latitude and longitude is from Google Earth.
Type in your address, and then move the cursor to the exact location of your
desktop. The latitude and longitude should be displayed at the bottom of the
screen.
Every hour or so the Quake Catcher software checks to make sure your
Desktop's clock is synchronized with the clock here at the Quake Catcher Network.
The clock here at the Quake Catcher Network is synchronized with an atomic
clock, so the the whole network is always on time.
The power sometimes goes out for a short period after earthquakes because of
broken power lines. If the power goes out, your Desktop will usually crash. You
can avoid this if you plug your computer to a Uninteruptable Power
Supply. The uninteruptable power supply will keep your computer running for
several minutes. This will provide enough time to save the seismic data to disk and turn
off the computer. When the computer is turned back on, the QCN server can then
request the seismic data for the earthquake.