Using smartphone pressure sensors to measure vertical velocities of elevators, stairways, and drones

Abstract

We measure the vertical velocities of elevators, pedestrians climbing stairs,\nand drones (flying unmanned aerial vehicles), by means of smartphone pressure\nsensors. The barometric pressure obtained with the smartphone is related to the\naltitude of the device via the hydrostatic approximation. From the altitude\nvalues, vertical velocities are derived. The approximation considered is valid\nin the first hundred meters of the inner layers of the atmosphere. In addition\nto pressure, acceleration values were also recorded using the built-in\naccelerometer. Numerical integration was performed, obtaining both vertical\nvelocity and altitude. We show that data obtained using the pressure sensor is\nsignificantly less noisy than that obtained using the accelerometer. Error\naccumulation is also evident in the numerical integration of the acceleration\nvalues. In the proposed experiments, the pressure sensor also outperforms GPS,\nbecause this sensor does not receive satellite signals indoors and, in general,\nthe operating frequency is considerably lower than that of the pressure sensor.\nIn the cases in which it is possible, comparison with reference values taken\nfrom the architectural plans of buildings validates the results obtained using\nthe pressure sensor. This proposal is ideally performed as an external or\noutreach activity with students to gain insight about fundamental questions in\nmechanics, fluids, and thermodynamics.\n