Added a PCB for a piezo electric element

Hardware/Microphone-piezo/README

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+A impedance buffer and amplifier for the xSoundsMicrophones project.
+
+The problem with piezoelectric and contact mics is that they are not well matched to typical audio inputs. 
+The reason why these devices often sound tinny is because the piezo sensor presents its signal through a series capacitance which is small, typically 15nF or less. When wired to a normal 50 kilohm line input this forms a 200Hz high-pass filter, which eliminates the bass. 
+Because the piezo disc has a very high impedance (1 MΩ typical), it should be buffered to avoid possible impedance mismatch with an existing audio system. This circuit acts as a impedance buffer, and some amplification does not hurt as long as it is around 40dB. 
+The best piezoelectric sensors for listening is based on Aluminum Nitride and molybdenum. PZT-5 also known as SensorTech BM500,Channel 5500,Morgan PZT5A1 is widely used.
+
+The diodes are there to avoid overloading the circuit if it is dropped or bumped in to something hard.
+
+NOAA technical memorandum NMFS 2008NOAA-TM-NMFS-SWFSC-417 also known as
+A guide to constructing hydrophones and hydrophone arrays for monitoringmarine mammal vocalizations,
+describes how to build a single crystal hydrophone.
+
+If the piezo electric crystals are a suitable distance and 45° degrees apart from each other in a flat circular array with 8  piezoelectric sensors,
+they should be compatible with Manyears or ODAS.
+
+Approximate values for fresh water and seawater, respectively, at surface pressure are 1450 around 1500 m/s.
+The speed of sound in water increases with increasing pressure, temperature and salinity.
+
+Also, read: https://github.com/Supermagnum/passiveSonar
+
+
+PCB:
+https://oshpark.com/shared_projects/I4DribPA