Capacitive sensor

1 . A method comprising:

measuring a first response of a guard sensor of a human machine interface using a first sensing signal having a first frequency;

measuring a second response of the guard sensor using a second sensing signal having a second frequency;

configuring a human input sensor of the human machine interface adjacent the guard sensor after measuring the first response and measuring the second response to select a sensor frequency based on the first response of the guard sensor and the second response of the guard sensor;

measuring a first response of the human input sensor using the sensor frequency; and

identifying a touch event on the human input sensor based on the first response of the human input sensor.

2 . The method of claim 1 , comprising:

determining a presence of an interference source based on the first response of the guard sensor and the second response of the guard sensor, wherein configuring the human input sensor comprises configuring the human input sensor responsive to determining the presence of the interference source.

3 . The method of claim 2 , wherein:

the interference source comprises a liquid impinging on the human machine interface; and

configuring the human input sensor comprises disabling the human input sensor.

4 . The method of claim 2 , wherein:

measuring the first response of the guard sensor and the second response of the guard sensor comprises measuring the first response of the guard sensor and the second response of the guard sensor with a shield electrode of the human machine interface enabled; and

the method comprises:

measuring a third response of the guard sensor using the first sensing signal with the shield electrode disabled; and

measuring a fourth response of the guard sensor using the second sensing signal with the shield electrode disabled; and

determining the presence of the interference source comprises differentiating between a touch event and a liquid impingement event on the guard sensor based on the third response of the guard sensor and the fourth response of the guard sensor.

5 . The method of claim 2 , wherein:

the interference source comprises a radio frequency interference source at the first frequency; and

configuring the human input sensor comprises selecting the second frequency as the sensor frequency.

6 . The method of claim 5 , comprising:

changing the first sensing signal to have a third frequency different than the first frequency; and

measuring the first response of the guard sensor using the first sensing signal with the third frequency.

7 . The method of claim 1 , comprising:

detecting a proximity event based on the first response and the second response.

8 . A human machine interface comprising:

a guard sensor;

a human input sensor adjacent the guard sensor; and

a controller configured to:

measure a first response of the guard sensor using a first sensing signal having a first frequency;

measure a second response of the guard sensor using a second sensing signal having a second frequency;

configure a sensor frequency of the human input sensor after measuring the first response and measuring the second response based on the first response of the guard sensor and the second response of the guard sensor;

measure a first response of the human input sensor using the sensor frequency; and

identify a touch event on the human input sensor based on the first response of the human input sensor.

9 . The human machine interface of claim 8 , wherein the controller is configured to:

determine a presence of an interference source based on the first response of the guard sensor and the second response of the guard sensor; and

configure the human input sensor responsive to determining the presence of the interference source.

10 . The human machine interface of claim 9 , wherein:

the interference source comprises a liquid impinging on the human machine interface; and

the controller is configured to disable the human input sensor responsive to the interference source comprising the liquid.

11 . The human machine interface of claim 9 , comprising:

a shield electrode, wherein:

the controller is configured to:

measure the first response of the guard sensor and the second response of the guard sensor with the shield electrode enabled;

measure a third response of the guard sensor using the first sensing signal with the shield electrode disabled;

measure a fourth response of the guard sensor using the second sensing signal with the shield electrode disabled; and

determine the presence of the interference source by differentiating between a touch event and a liquid impingement event on the guard sensor based on the third response of the guard sensor and the fourth response of the guard sensor.

12 . The human machine interface of claim 9 , wherein:

the interference source comprises a radio frequency interference source at the first frequency; and

the controller is configured to select the second frequency as the sensor frequency.

13 . The human machine interface of claim 12 , wherein the controller is configured to:

change the first sensing signal to have a third frequency different than the first frequency; and

measure the first response using the first sensing signal with the third frequency.

14 . The human machine interface of claim 13 , wherein the controller is configured to:

detect a proximity event based on the first response using the first sensing signal with the third frequency and the second response.

15 . A human machine interface comprising:

a guard sensor;

a human input sensor adjacent the guard sensor; and

a controller configured to:

detect an interference event on the guard sensor using a frequency hopping technique with a set of sensing frequencies;

detect a touch event on the human input sensor using a single frequency technique; and

configure a sensor frequency of the human input sensor for the single frequency technique based on the interference event after detecting the interference event.

16 . The human machine interface of claim 15 , wherein:

the interference event comprises a liquid impingement event; and

the controller is configured to disable the human input sensor responsive to the interference event comprising the liquid impingement event.

17 . The human machine interface of claim 15 , comprising:

a shield electrode, wherein:

the controller is configured to:

detect the interference event with the shield electrode enabled;

detect the interference event with the shield electrode disabled; and

differentiate between a touch event and a liquid impingement event as the interference event based on detecting the interference event with the shield electrode disabled.

18 . The human machine interface of claim 15 , wherein:

the interference event comprises a radio frequency interference event at a first frequency in the set of sensing frequencies; and

the controller is configured to exclude the first frequency from the set of sensing frequencies responsive to detecting the interference event.

19 . The human machine interface of claim 15 , wherein:

the interference event comprises a radio frequency interference event at a first frequency in the set of sensing frequencies; and

the controller is configured to exclude the first frequency from being selected as the sensor frequency responsive to detecting the interference event.

20 . The human machine interface of claim 15 , wherein the controller is configured to:

detect a proximity event using the guard sensor.