Touchpad force calculation using no-touch capacitance

A computing device, comprising:

• a force sensing touchpad comprising:
• a base plate comprising a base electrode;
• and
• a printed circuit board (PCB) resiliently spaced from the baseplate and comprising a capacitive force sensing electrode and a shielded electrode located between a first shielding layer and a second shielding layer to substantially isolate the shielded electrode from changes in capacitance caused by movement of the PCB;
• a processor;
• and
• a memory storing instructions executable by the processor to:
• determine that the touchpad is not being touched;
• at least on condition of determining that the touchpad is not being touched, calculate a no-touch capacitance value of the PCB;
• after calculating the no-touch capacitance value, determine that the touchpad is being touched;
• while the touchpad is being touched, calculate a measured change in capacitance by subtracting the no-touch capacitance value from a touch-based capacitance value;
• calculate an environmental change in capacitance at the shielded electrode;
• use the environmental change in capacitance to adjust the measured change in capacitance to an adjusted measured change in capacitance;
• and
• at least on condition that the touchpad is being touched, use the adjusted measured change in capacitance to estimate a force F exerted on the touchpad.

A computing device, comprising:

• a force sensing touchpad comprising:
• a base plate comprising a base electrode;
• and
• a printed circuit board (PCB) resiliently spaced from the baseplate and comprising a capacitive force sensing electrode;
• a processor;
• and
• a memory storing instructions executable by the processor to:
• determine that the touchpad is not being touched;
• at least on condition of determining that the touchpad is not being touched, calculate a no-touch capacitance value of the PCB;
• after calculating the no-touch capacitance value of the PCB, determine that the touchpad is being touched;
• while the touchpad is being touched, calculate a first measured change in capacitance by subtracting the no-touch capacitance value of the PCB from a first touch-based capacitance value;
• use the first measured change in capacitance to estimate a first force F exerted on the touchpad;
• after determining that the touchpad is being touched, determine the touchpad is not being touched;
• at least on condition that the touchpad is not being touched, recalculate the no-touch capacitance value to a recalculated no-touch capacitance value;
• after recalculating the no-touch capacitance value, determine the touchpad is being touched;
• while the touchpad is being touched, calculate a second measured change in capacitance by subtracting the recalculated no-touch capacitance value from a second touch-based capacitance value;
• use the second measured change in capacitance to estimate a second force F exerted on the touchpad.