An apparatus for determining the volume of fluid dispensed comprising: an acoustic volume sensor comprising: a structure containing a fixed-volume chamber , a first port , and a measurement chamber , wherein the first port acoustically couples the fixed-volume chamber to the measurement chamber to form an acoustically contiguous region; a dispensing diaphragm arranged to define a boundary of the measurement chamber; a dispensing chamber containing a variable fluid volume, wherein the dispensing chamber and measurement chamber share a boundary defined by the dispensing diaphragm; and characterized by a printed circuit board disposed within the structure, between the reference chamber and the fixed volume chamber such that the printed circuit board is arranged to define a boundary of the reference chamber within the structure that separates the fixed volume chamber from the reference chamber, the printed circuit board including an electronics assembly arranged on the printed circuit board, the electronics assembly comprising: a loudspeaker acoustically coupled to the fixed-volume chamber , wherein the loudspeaker excites the acoustically contiguous region; a sensing microphone acoustically coupled to the measurement chamber via a second port , the sensing microphone producing a first signal based on the response of the measurement chamber to excitement by the loudspeaker; and a reference microphone acoustically coupled to the reference chamber , the reference microphone producing a second signal based on the response of the reference chamber to excitement by the loudspeaker. a structure containing a fixed-volume chamber , a first port , and a measurement chamber , wherein the first port acoustically couples the fixed-volume chamber to the measurement chamber to form an acoustically contiguous region; a dispensing diaphragm arranged to define a boundary of the measurement chamber; a dispensing chamber containing a variable fluid volume, wherein the dispensing chamber and measurement chamber share a boundary defined by the dispensing diaphragm; and characterized by a printed circuit board disposed within the structure, between the reference chamber and the fixed volume chamber such that the printed circuit board is arranged to define a boundary of the reference chamber within the structure that separates the fixed volume chamber from the reference chamber, the printed circuit board including an electronics assembly arranged on the printed circuit board, the electronics assembly comprising: a loudspeaker acoustically coupled to the fixed-volume chamber , wherein the loudspeaker excites the acoustically contiguous region; a sensing microphone acoustically coupled to the measurement chamber via a second port , the sensing microphone producing a first signal based on the response of the measurement chamber to excitement by the loudspeaker; and a reference microphone acoustically coupled to the reference chamber , the reference microphone producing a second signal based on the response of the reference chamber to excitement by the loudspeaker. a loudspeaker acoustically coupled to the fixed-volume chamber , wherein the loudspeaker excites the acoustically contiguous region; a sensing microphone acoustically coupled to the measurement chamber via a second port , the sensing microphone producing a first signal based on the response of the measurement chamber to excitement by the loudspeaker; and a reference microphone acoustically coupled to the reference chamber , the reference microphone producing a second signal based on the response of the reference chamber to excitement by the loudspeaker. <EOS>