An optical trocar assembly has an elongated tubular member for receiving an endoscope which defines a longitudinal axis and has an open proximal end and a closed, optically clear distal end which is adapted for penetrating body tissue. When the output of the piezoelectric transformer is short-circuited to GND, the output detection voltage abruptly drops to almost 0 and becomes lower than a reference voltage. The substantially rigid sensor structure includes at least one capacitive pressure sensor. The processing circuit further configured to create a second acoustic fingerprint from a second signal from the microphone and compare the first acoustic fingerprint to the second acoustic fingerprint.