It is possible to add a Piezo Alarm to the detector circuit to tell you that a "seismic event", is being detected by the seismograph. There is no way of knowing if the seismic event is likely to generate a Tsunami; even Tsunami Warning Centres cannot tell. If the alarm sounded and I lived at sea level near the coast, I know which way I would run.
The alarm circuit can easily fit on the right hand end of the detector board. A 5k or 10k trimpot or variable resistor is wired from the op amp output to the earth wire. It is in parallel with the resistors that make the output voltage divider. The high and low outputs still work and can feed the signal to the data logger as before. The middle leg of the trimpot or variable resistor is connected to the base leg of a BC547 transistor. When a quake is detected the voltage on the base leg will rise above 0.6 volts, switching the transistor on and allowing current to flow through a 90dB piezo siren. A 1k resistor from the positive line limits the maximum current flow through the transistor and siren.
You need to set the trimpot or variable resistor so that the siren is just off when the bar is still. If you don't have a data logger and computer it is possible to just use the alarm to tell you that an earthquake has occurred. It might also be an option for teachers who have the seismograph set up in storeroom or prep room where you are unlikely to see an earthquake live on the computer. The alarm circuit will alert you to look at the monitor.
Like the trigger option for some of the data loggers it might take a while to set the trigger level so that it si sensitive enough but not too "trigger happy".
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Last Update: Monday, 30-Apr-2012 15:05:52 EST