Micropower capacitance-based proximity sensor

A proximity detector for detecting the presence of a user in a predetermined location adjacent to an electronic device, comprising:

• a housing, the housing containing the electronic device;
• a power supply, the power supply providing power to the electronic device, and mounted within the housing;
• a first electrode, a second electrode and a third electrode mounted in an outer wall of the housing;
• a first capacitor comprised of the first electrode and the second electrode;
• a second capacitor comprised of the second electrode and the third electrode, the first electrode, second electrode and third electrode positioned within the housing such that the presence of the user at the predetermined location will effect either the first capacitor or the second capacitor, but not both;
• a proximity detection circuit coupled to the electronic device, the first capacitor, the second capacitor, and to the power supply, the proximity detection circuit including:
• a logic gate driven by a clock, the logic gate coupled to the first capacitor and the second capacitor, and receiving power from the power supply, the logic gate and clock providing an input signal into the first capacitor and the second capacitor;
• a first amplifier and filter coupled to the first capacitor for receiving a first signal from the first capacitor, and providing a first output;
• a second amplifier and filter coupled to the second capacitor for receiving a second signal from the second capacitor, and providing a second output;
• an inverter coupled to the second amplifier and filter, for inverting the second output;
• and
• a summing circuit, the summing circuit coupled to the inverter and the first amplifier and filter, wherein the summing circuit produces a first control signal when the first output is equal to the second output, and produces a second control signal when the first output is not equal to the second output;
• wherein, the electronic device only receives full power from the power supply when the summing circuit generates the second output.

A proximity based power system for use in automatically activating an electronic device in response to the presence of a user at a predetermined location relative to the electronic device, the power system comprising:

• a first electrode mounted within a housing;
• a second electrode mounted with the housing on a first side of the first electrode;
• a third electrode mounted within the housing on a second side of the first electrode, the second side being opposite the first side;
• a capacitance mismatch detection circuit for monitoring a first capacitance level between the first electrode and the second electrode, and for monitoring a second capacitance between the first electrode and the third electrode, the capacitance mismatch detection circuit for producing a first output signal when the first capacitance and the second capacitance are substantially equal, and producing a second output signal when the first capacitance and the second capacitance are mismatched due to the presence of the user at the predetermined location;
• a power supply;
• and
• a power controller coupled to the output of the power supply and the mismatch detection circuit, wherein the power controller will allow power to be applied to the electronic device when the second output signal is present.

A power up system for activating an electronic device when the user is detected to be using an eyepiece of the electronic device and deactivating the electronic device when the user is no longer using the eyepiece, the power up system comprising:

• a clocking circuit for providing an driving signal;
• a first capacitor positioned adjacent the eyepiece and attached to the clocking circuit so as to receive the driving signal;
• a second capacitor positioned adjacent the eyepiece and opposite the first capacitor, the second capacitor is attached to the clocking circuit so as to receive the driving signal, the first capacitor and the second capacitor having substantially equal capacitance values when a user is not using the eye piece, but having different capacitance values when the user is using the eyepiece;
• a first amplifier coupled to the first capacitor to receive a first capacitor signal from the first capacitor and produce a first amplifier output signal proportional to the first capacitor signal;
• a second amplifier coupled to the first capacitor to receive a second capacitor signal from the second capacitor and produce a second amplifier output signal proportional to the second capacitor signal;
• an inverter coupled to the second amplifier to receive the second amplifier output signal and produce an inverted signal;
• and
• a summing circuit for receiving the first amplifier output and the inverted signal and producing a summing output equal to the sum of the first amplifier output and the inverted signal, wherein the summing output is substantially zero when the first capacitance and second capacitance are substantially equal, and wherein the summing output is a non-zero value when either the first capacitor or the second capacitor are occluded by the user, the non-zero value being output to the electronic device causing the electronic device to be activated.