Tap detection
First Claim
1. An acclerometer system for determining if a device has been tapped, the system comprising:
- accelerometer circuitry outputting a temporal acceleration signal;
an input for receiving a jerk select signal;
a register for storing the temporal acceleration signal at time N−
1;
a subtraction circuit receiving from the register the temporal acceleration signal at time N−
1 and subtracting the temporal acceleration signal at time N−
1 from the temporal acceleration signal at time N producing a jerk signal;
a multiplexor for receiving the jerk select signal from the input, the temporal acceleration signal from the accelerometer circuitry, and the jerk signal from the subtraction circuit and for outputting a multiplexor output signal of either the temporal acceleration signal or the jerk signal dependent on the jerk select signal; and
a computation module receiving the multiplexor output signal and comparing the multiplexor output signal to at least one threshold to determine if the device has been tapped.
3 Assignments
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Accused Products
Abstract
Methodology and circuitry for determining if a device, such as a cellular phone or personal digital assistant has been tapped is disclosed. The device includes an accelerometer and in response to an acceleration, the accelerometer outputs an acceleration signal. The accelerometer may continuously output an acceleration signal even if no acceleration occurs. A tap detection device receives the temporally sampled acceleration signal and takes the first derivative of the temporally sampled acceleration signal producing one or more derivative values. The tap detection system compares each derivative value to a threshold value and if the derivative value exceeds the threshold a tap is detected. By taking the derivative of the acceleration signal, the noise floor for the acceleration signal is reduced leading to more accurate results with less false positives and less positive negatives.
17 Citations
8 Claims
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1. An acclerometer system for determining if a device has been tapped, the system comprising:
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accelerometer circuitry outputting a temporal acceleration signal; an input for receiving a jerk select signal; a register for storing the temporal acceleration signal at time N−
1;a subtraction circuit receiving from the register the temporal acceleration signal at time N−
1 and subtracting the temporal acceleration signal at time N−
1 from the temporal acceleration signal at time N producing a jerk signal;a multiplexor for receiving the jerk select signal from the input, the temporal acceleration signal from the accelerometer circuitry, and the jerk signal from the subtraction circuit and for outputting a multiplexor output signal of either the temporal acceleration signal or the jerk signal dependent on the jerk select signal; and a computation module receiving the multiplexor output signal and comparing the multiplexor output signal to at least one threshold to determine if the device has been tapped. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification