Directional tap detection algorithm using an accelerometer

摘要

A directional tap detection algorithm and a single tri-axis accelerometer are employed to extend the number of unique button less input commands available for a small mobile electronic device. The algorithm analyzes acceleration data from the tri-axis accelerometer to detect the direction and number of taps imparted to any of the six sides of a housing of the device, yielding 12 unique inputs. The algorithm employs a parameter referred to as the performance index (PI) to identify tap induced movements. The PI is determined by calculating the time derivative of each acceleration signal for each axis and then calculating the sum of the absolute values of the calculated acceleration derivatives. A tap is determined to have occurred if the sum exceeds a threshold value for a predetermined amount of time. If a second tap is detected within a predetermined time after the first tap, then a double tap is determined to have occurred.