Detection of a conductive object during an initialization process of a touch-sensing device
A method and system for detecting a presence of a conductive object proximate to a capacitive sense element during an initialization process of a touch-sensing device. A reference sense element is calibrated to produce a sensing parameter value. A capacitance of a plurality of capacitive sense elements is measured based on the sensing parameter value, and compared to a baseline capacitance value stored in a non-volatile memory of the touch-sensing device. The presence of a conductive object proximate to a capacitive sense element is detected when a difference between the measured capacitance and the stored baseline capacitance value is greater than a threshold value.
1. A method, comprising:
during an initialization process of a touch-sensing device:
measuring a capacitance of a reference sense element disposed on a second side of a printed circuit board of the touch-sensing device, wherein the measured capacitance is responsive to an environmental condition and is not responsive to a conductive object,
comparing the measured capacitance of the reference sense element to a target measurement output value, and
calibrating a capacitance measurement of the reference sense element to produce a sensing parameter value;
comparing a capacitance measured on each of a plurality of capacitive sense elements disposed on a first side of the printed circuit board based on the sensing parameter value to a baseline capacitance value for each of the plurality of capacitive sense elements to determine a capacitance difference value; and
detecting a presence of the conductive object proximate to a capacitive sense element when the capacitance difference value for the capacitive sense element is greater than a threshold value.
2. The method of claim 1 , wherein calibrating the capacitance measurement of the reference sense element further comprises adjusting a sensing parameter to the sensing parameter value to set the measured capacitance of the reference sense element to the target measurement output value.
3. The method of claim 2 , wherein the sensing parameter is a current of a current source connected to a capacitance sensor of the touch-sensing device.
4. The method of claim 2 , wherein the sensing parameter is a voltage of a voltage source connected to a capacitance sensor of the touch-sensing device.
5. The method of claim 2 , wherein the sensing parameter is programmable by a processing device.
6. The method of claim 1 , wherein the presence of the conductive object proximate to the capacitive sense element is detected during the initialization process of the touch-sensing device.
7. The method of claim 1 , wherein the baseline capacitance value for each of the plurality of capacitive sense elements is stored in a non-volatile memory.
8. A system, comprising:
a processing device coupled to a capacitance sensor, the capacitance sensor comprising:
a printed circuit board comprising a first side including a plurality of capacitive sense elements disposed thereon, and a second side including a reference sense element disposed thereon, and
a sensing parameter,
wherein the processing device is to:
measure a capacitance of the reference sense element, wherein the measured capacitance is responsive to an environmental condition and is not responsive to a presence of a conductive object,
compare the measured capacitance of the reference sense element to a target measurement output value,
adjust the sensing parameter to a sensing parameter value to set a measured capacitance of the reference sense element to the target measurement output value,
compare a capacitance of each of the plurality of capacitive sense elements to a baseline capacitance value for each of the plurality of capacitive sense elements to determine a capacitance difference value, and
detect a presence of the conductive object proximate to a capacitive sense element when the capacitance difference value for the capacitive sense element is greater than a threshold value.
9. The system of claim 8 , wherein the capacitance sensor is to measure the capacitance of each of the plurality of capacitive sense elements based on the sensing parameter value.
10. The system of claim 8 , wherein the baseline capacitance value for each of the plurality of capacitive sense elements is stored in a non-volatile memory of the touch-sensing device.
11. The system of claim 8 , wherein the presence of the conductive object proximate to the capacitive sense element is detected during an initialization process of the touch-sensing device.
12. The system of claim 8 , wherein the reference sense element is not responsive to the presence of the conductive object during an initialization process of the touch-sensing device.
13. The system of claim 8 , wherein the sensing parameter is a programmable current.
14. The system of claim 8 , further comprising a printed circuit board comprising an overlay covering the reference sense element such that the reference sense element is not responsive to a presence of a conductive object proximate to the reference sense element during an initialization process of the touch-sensing device.
15. A non-transitory computer-readable medium including data that, when accessed by a processing device, causes the processing device to perform operations comprising:
during an initialization process power up of a touch-sensing device, measuring a capacitance of a reference sense element disposed on a second side of a printed circuit board of the touch-sensing device, wherein the measured capacitance is responsive to an environmental condition and is not responsive to a presence of a conductive object, comparing the measured capacitance of the reference sense element to a target measurement output value, and calibrating a measurement of a reference sense element to produce a sensing parameter value;
comparing a capacitance measured on each of a plurality of capacitive sense elements disposed on a first side of the printed circuit board based on the sensing parameter value to a baseline capacitance value stored in a non-volatile memory for each of the plurality of capacitive sense elements to determine a capacitance difference value; and
detecting a presence of the conductive object proximate to a capacitive sense element during the initialization process power up of the touch-sensing device when the capacitance difference value for the capacitive sense element is greater than a touch threshold value.
16. The non-transitory computer-readable medium of claim 15 , wherein the operations further comprise adjusting a sensing parameter to a sensing parameter value to set a capacitance of the reference sense element to a target measurement output value.
17. The non-transitory computer-readable medium of claim 16 , wherein the sensing parameter is a current of a current source connected to a capacitance sensor of the touch-sensing device.
18. The non-transitory computer-readable medium of claim 15 , wherein the capacitance on the capacitive sense element is measured by a capacitance sensor.