Estimating Touch Force with Barometric Pressure Sensors

Abstract

Finger pressure offers a new dimension for touch interaction, where input is defined by its spatial position and orthogonal force. However, the limited availability and complexity of integrated force-sensing hardware in mobile devices is a barrier to exploring this design space. This paper presents a synthesis of two features in recent mobile devices-a barometric sensor (pressure altimeter) and ingress protectionto sense a user's touch force. When a user applies force to a device's display, it flexes inward and causes an increase in atmospheric pressure within the sealed chassis. This increase in pressure can be sensed by the device's internal barometer. However, this change is uncontrolled and requires a calibration model to map atmospheric pressure to touch force. This paper derives such a model and demonstrates its viability on four commercially-available devices (including two with dedicated force sensors). The results show this method is sensitive to forces of less than 1 N, and is comparable to dedicated force sensors. CCS CONCEPTS • Human-centered computing → Ubiquitous and mobile computing systems and tools; Touch screens; • Hardware → Sensors and actuators.

Barometers Can Hear, and Sense Finger Taps

“…Detecting taps. Quinn [7] recently showed that, in devices with ingress protection, forces on touchscreen can be detected using the device's internal barometer. To this end, a robotic arm was programmed to perform five second touch contacts with three different force levels (1, 3, and 5N).…”

“…Unlike the 5-second robotic arm touch contacts in [7], finger taps have a short touchscreen contact time. In our experiment, the touchscreen contact time of a finger tap ranged from 24ms to 183ms, with the average of 85ms.…”

“…In our experiment, the touchscreen contact time of a finger tap ranged from 24ms to 183ms, with the average of 85ms. As stated in [7] if a 2 Over-the-horizon ringtone, extracted from Samsung Galaxy S10 Plus. user's input force changes too quickly, it may not be captured by the barometer.…”

“…In a recent work, Quinn [7] proposed to use barometers to estimate touch forces in an attempt to provide force sensing functionality in smartphones that lack an integrated forcesensing hardware. To this end, Quinn showed that barometers on smartphones with ingress protection can estimate robotic forces on their touchscreen.…”

“…Finally, the flow rate of the barometric vent can also become a limiting factor. As stated in [7], if a user's input force changes either too quickly or too slowly, it may not be captured by the barometer.…”