Apparatus and method for processing capacitor sensor signals using digital frequency shift measurement techniques with floating reference

A method of object detection comprising the steps of:

• providing a field generating circuit operative to produce a sensing field signal and to generate a capacitive sensing field, said sensing field signal operative to change in response to an object moving within capacitive sensing field;
• and
• providing a monitor circuit in communication with said field generating circuit operative to monitor said sensing field signal, wherein said step of providing a monitor circuit further comprises the steps of:
• providing a reference signal counter operative to count digital pulses and store a first digital value that corresponds to the number of digital pulses counted during a first cycle of said signal field signal;
• providing a field generator signal counter operative to receive and store said first digital value from said reference signal counter, and operative to begin counting down from said first digital value at each new cycle of said sensing field signal, and operative to continue counting down until said field generator signal counter equals zero or until said new cycle ends, and operative to count to a second digital value that corresponds to the difference between the number of digital pulses occurring during said new cycle and the value stored in the reference signal counter;
• providing a threshold compare circuit operative to receive said difference value and compare it to a predetermined value, and operative to generate an object detection signal when said difference value exceeds a predetermined threshold value;
• and
• providing at least one alarm mechanism operative to receive said alarm signal and activate at least one alarm device.