earthquake alarm circuit

 (1) The circuit working principle diagram is the electrical principle diagram of the annunciator
. In the figure, A is a copper cylinder, and B is a copper
plate with a hole in the middle. A and B are fixed on the seismic detection frame. Since the round hole of the copper plate
is insulated from the copper cylinder, the relay is usually in the released state and the power supply
does not consume power, but the alarm maintains the monitoring state.
    When an earthquake of magnitude 4 or above occurs, copper cylinder A tilts and
swings (the gap between A and B is 2mm). A and B collide, causing
the relay coil to connect to the power supply , its normally open contact closes, and the speaker sounds
an alarm. At the same time, it closes and turns on the lights in the passage, allowing
people to move quickly.
    In the circuit, VT1, VT2, etc. form an ultra-low-frequency sine wave oscillator, and VT3, VT4, etc. form an audio oscillator. These two oscillators
are modulated through the resistor R. Therefore, the output potential of the ultra-low frequency sine oscillator directly affects the working state of the VT3 base.
    SB in the picture is the release button of the earthquake alarm.