Apparatus and methods for measuring and detecting variations in the value of a capacitor

A proximity sensor apparatus for determining an approach, nearness and retreat of an object with respect to itself, said proximity sensor comprising:

• a substrate defining a sensor location;
• a sensor including a transmitting electrode and a receiving electrode disposed on said substrate in electromagnetic field-defining relation to each other and forming a variable capacitive element between said electrodes;
• a detector circuit including a substantially constant load impedance R connectible in series with said sensor, means for providing a voltage input V of known wave form to said detector circuit, means for measuring an instantaneous sample voltage v across said sensor after a known time interval T has elapsed, said sampling moment being in a predetermined fixed phase relationship to the input voltage V and means for precisely controlling said time interval T;
• means for connecting said sensor to said detector circuit in series with said load impedance R;
• means for calculating and storing a numerical resultant indicative of a sampled value of the sensor, said numerical resultant being representative of a measured variable per se or of a relation expression of a combination of variables, said variables including wave form, v, V, T and R;
• means for analyzing changes in said stored resultants with respect to time in excess of an assigned variation amount and, if a change in excess of said assigned variation amount is identified, for providing a sensor activation output signal, whereby, approach, nearness, and retreat of an object into field-disturbing proximity to said sensor causes changes in the amount of field energy through the sensor, causing the value of capacitance of the sensor to vary and also its calculated and stored resultant to vary in relation to said field changes, thereby permitting the sensor to exhibit characteristics of a variable capacitive divider in respect to the said object, consisting of a pair of first and second variable capacitors in which the capacitive value of said first capacitor increases as the capacitive value of the second capacitor decreases and vice versa.

A human to machine input command interface comprising:

• a control panel defining an input interface location having a outwardly facing human contact surface;
• a plurality of proximity sensor cells arranged in an array disposed on a substrate adjacent said control panel opposite said human contact surface for detecting intentional human finger input control commands by sensing the approach and retreat of a finger with respect to a key defined on the human contact surface overlying a sensor cell location in said array, each sensor cell including an associated address in said array;
• each sensor cell including a transmitting electrode and a receiving electrode disposed on said substrate in electromagnetic field-defining relationship to each other and forming a variable capacitive element between said electrodes, and means for conditioning signals associated with said receiving electrode for providing a conditioned signal output for each sensor cell in said array;
• a detector circuit including means for providing a voltage input V having a known wave form to all the sensor cells in said array, means for measuring an instantaneous sample voltage v output from said sensor conditioning element after a known time interval T has elapsed, said sampling moment being in a predetermined fixed phase relationship to the voltage input V, and means for providing a stable and accurate time base for precisely controlling said time interval T;
• means for successively sampling each sensor cell in said array in a predetermined sequential sampling order including means for sequentially connecting the transmitting electrode and the conditioned signal output of each sensor cell to said detector circuit;
• means for calculating and storing a processed numerical resultant for each cell sampled and for each successive sampling sequence, said processed numerical resultant being representative of a measured variable per se or of a relational expression of a combination of variables, said variables including v, V, wave form and T;
• means for analyzing the stored resultants for each sensor cell address in the array with respect to time to detect changes in the value of said stored resultants over time in excess of an assigned variation amount;
• means for analyzing and storing information regarding trends of change in the stored resultants for a given sensor cell over time to identify changes in trends associated with an approach and a retreat of a finger to provide a reliable determination that an intentional finger approach input command has occurred;
• and means for forming a command signal and for communicating said command signal to said machine in response to each said finger approach input command.

A method for detecting variations in value of an analog electrical input signal in excess of an assigned variation amount in the presence of electrical noise, said method comprising:

• (a) providing a reference value for said electrical input signal and a first value for said first assigned variation amount;
• (b) sampling the analog electrical input signal and storing a processed numerical resultant representative of that sampled value of said analog input signal;
• (c) comparing the difference between the stored numerical resultant obtained in step (b) and the said reference value provided in step (a) with said first assigned variation amount;
• (d) if the compared values from step (c) for two consecutive sampling steps exceeds the first assigned variation amount thereby identifying that the signal is varying in excess of the assigned variation amount;
• (e) thereafter, reducing the value of said first assigned variation amount to a smaller second assigned variation amount;
• (f) continuing said comparing steps until two consecutive comparisons for two consecutive sampling steps are greater than said second assigned variation amount and thereby identifying that said analog signal has returned to its normal reference value;
• and
• (g) thereafter, increasing the value of said second assigned variation amount to said first assigned variation amount.

A method for reducing electrical noise associated with an analog electrical signal to provide a filtered digital representation of said analog signal, said method comprising:

• (a) providing an analog electrical signal in the added presence of noise;
• (b) providing a reversible counter;
• (c) digitizing said analog signal at a higher rate than an expected rate of variation in time of said analog signal;
• (d) providing means for storing said digitized values in memory;
• (e) storing said first said digitized value in memory;
• (f) reading a next digitized value;
• (g) comparing said next value against the stored value;
• (h) if the next value is greater than the stored value, incrementing said counter, and if the next value is smaller than the stored value then decrementing said counter;
• (i) if the counter had an overflow and generated a carry signal, then adjusting the stored value by one count in the up direction;
• (j) if the counter had an underflow and generated a borrow signal then adjusting the stored value by one count in the down directing;
• (k) thereafter, repeating steps (f)-(j) for all subsequent read cycles of said input signal, whereby, the stored value in said memory means is the filtered value of the signal.

A proximity sensor apparatus for determining an approach, nearness and retreat of an object with respect to itself, said proximity sensor comprising:

• a substrate defining a sensor location;
• a sensor including a transmitting electrode and a receiving electrode disposed on said substrate in electromagnetic field defining relation to each other and configured to form a variable capacitor between said electrodes, such that when an outside conductive object is disposed in proximity to said sensor, the capacitor formed by said electrodes exhibits the characteristics of a substantially variable capacitor and exhibits the characteristics of a capacitive divider in respect to said object in which the variable capacitance between the two electrodes is substantially reduced and a new capacitance between the receiving electrode and the object is formed;
• and
• means for detecting a drop in amplitude due to the forming of said capacitive divider and a change in shape due to the substantial variation of capacitance between said electrodes of a signal applied to the transmitting electrode and arriving at the receiving electrode.