This microbarograph was constructed by adapting the datalogging optical seismograph to measure preassure changes. The small propane tank is used as a reference volume for one end of a manometer with the other end open to atmoshpere through the 2 port manifold created from a washing machine water control valve. The reference volume vents through a pinhole in the end of the plastic tube protruding from the original safety valve hole. A copper tube is soldered into the side to connect the clear manometer tube and a small float shades the optical detector across the fluid level. The detector works very well in the range of 0.1 to 1.0 hz. Above 1.0 hz the inertia of the fluid seems to cause a low pass filter and below 0.1 hz the reference vent system provides high pass filtering. In testing, raising the instrument in steps yielded a calibration of 845 ad counts per inch of elevation change. Bouncing on an exercise ball anywhere in the house causes pressure waves to spike the indicator record.
This is FFT of wind with house door open.
This is FFT of model helicopter shadow on optical pickup. Note the higher frequencies are not lost by the electronics.
This is FFT of electronic system with no physical input.
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