This paper describes the realization of a sensor capable of measuring the volume of a drop in free fall. The sensor realized is made of a simple low-cost red laser and a photodiode and optics to focus the beam on the light sensor. In this way, when the drop is falling down, it is possible to estimate its volume from the signal generated on the photodiode while getting through the laser beam.
This system may be very useful together with a drip chamber to have accurate and low-cost volume and flow rate measurements of the infused substances.