Proximity detection circuit and method of detecting capacitance changes

• US 20040160234A1
• Filed: 02/20/2004
• Published: 08/19/2004
• Est. Priority Date: 02/09/2001
• Status: Active Grant

• Current Assignee: GPCP IP Holdings LLC
• Original Assignee: Georgia-Pacific Corporation
• Inventors: Knittle, John J,, Myers, Gary Edwin, Denen, Dennis Joseph, Groezinger, Charles W.
• Granted Patent: US 7,102,366 B2
• Time in Patent Office: Days
• US Class Current: 324/679
• CPC Class Codes: A47K 10/36 with mechanical dispensing, roll switching or cutting devices
• CPC Class Codes: A47K 10/3625 with electronic control means
• CPC Class Codes: A47K 10/3687 with one or more reserve rolls
• CPC Class Codes: A47K 2010/3668 Detection of the presence of a user
• CPC Class Codes: H05F 3/02 by means of earthing connections

Abstract

Apparatus for dispensing paper from rolls which feeds continuously, roll to roll, and does not require extra procedure to bring stub roll into position. The apparatus has means for holding and positioning at least first and second rolls of paper with respect to each other; means for dispensing paper from the first roll; means for dispensing paper from the first and second rolls simultaneously when the first roll reduces to a predetermined diameter of paper, means for positioning the depleted first roll for replacement without the necessity of removing the second roll; and means for dispensing from the second and replacement rolls simultaneously when the second roll reduces to a predetermined diameter of paper. The apparatus also has a proximity sensor, which senses when a hand is placed near the dispenser, and thereupon dispenses a set amount of towel. The proximity sensor incorporates “static” and noise immunity circuitry.

Claims

1. A proximity detection circuit comprising:

an antenna;

an oscillator circuit adapted to provide charge to the antenna;

an operational amplifier being operated as a unity gain follower and receiving an antenna signal from the antenna, the antenna signal being representative of an external capacitive load on the antenna;

a detector circuit receiving the antenna signal via the operational amplifier and being adapted to output a detection signal in response to changes in the antenna signal; and

a comparator receiving the detection signal and being adapted to generate an output signal in response thereto.

2. The proximity detection circuit of claim 1 further comprising at least one static protection circuit having at least one first diode conducting away from ground and at least one second diode conducting toward a supply voltage.

3. The proximity detection circuit of claim 1, wherein the detector circuit comprises a voltage peak detector.

4. The proximity detection circuit of claim 1 further comprising a low-pass filter electrically coupled between the detector circuit and the comparator.

5. The proximity detection circuit of claim 1 further comprising an amplifier electrically coupled between the detector circuit and the comparator.

6. The proximity detection circuit of claim 1, wherein the comparator is adapted to generate the output signal when the detection signal has a predetermined voltage level as compared to a reference voltage.

7. The proximity detection circuit of claim 6 further comprising a switch electrically coupled to the comparator, the switch being adapted to adjust the reference voltage.

8. A proximity detection circuit comprising:

an antenna;

means for charging the antenna with an oscillating signal;

an operational amplifier being operated as a unity gain follower and receiving an antenna signal from the antenna, the antenna signal being representative of an external capacitive load on the antenna;

detection means electrically coupled to the operational amplifier for detecting changes in the antenna signal and for generating a detection signal in response thereto; and

means for generating an output signal in response to the detection signal.

9. The proximity detection circuit of claim 8 further comprising at least one static protection circuit having at least one first diode conducting away from ground and at least one second diode conducting toward a supply voltage.

10. The proximity detection circuit of claim 8 further comprising means for filtering alternating current interference frequencies from the detection signal.

11. The proximity detection circuit of claim 8 further comprising means for amplifying the detection signal.

12. A method of detecting capacitance changes comprising:

charging an antenna with an oscillating signal;

detecting changes in an antenna signal with a detector circuit, the antenna signal being representative of an external capacitive load on the antenna;

buffering an impedance mismatch between the antenna and the detector circuit with an operational amplifier operated as a unity gain follower;

generating a detection signal from the detector circuit in response to changes in the antenna signal; and

generating an output signal in response to the detection signal.

13. The method of claim 12, wherein generating the output signal includes comparing the detection signal to a reference voltage.

14. The method of claim 12, wherein charging the antenna with the oscillating signal includes charging the antenna with an oscillating asymmetric signal.

15. The method of claim 12, wherein detecting changes in the antenna signal includes detecting a peak voltage.

16. The method of claim 12 further comprising preventing oscillation by including a current limiting resistor at an output terminal of the operational amplifier.

17. The method of claim 12 further comprising filtering out alternating current interference frequencies from the detection signal.

18. The method of claim 12 further comprising amplifying the detection signal.

19. The method of claim 12 further comprising filtering out changes in DC voltage levels from the detection signal while passing transient portions thereof.

20. A method of detecting capacitance changes comprising:

charging an antenna with an oscillating signal;

providing protection from static utilizing at least one static protection circuit comprising at least one first diode adapted to conduct away from ground and at least one second diode adapted to conduct toward a supply voltage;

detecting changes in an antenna signal with a detector circuit, the antenna signal being representative of an external capacitive load on the antenna;

generating a detection signal from the detector circuit in response to changes in the antenna signal; and

generating an output signal in response to detection of changes in the detection signal.

21. The method of claim 20 wherein generating the output signal includes comparing the detection signal to a reference voltage.

22. The method of claim 20, wherein charging the antenna with the oscillating signal includes charging the antenna with an oscillating asymmetric signal.

23. The method of claim 20, wherein detecting changes in the antenna signal includes detecting a peak voltage.

24. The method of claim 20 further comprising preventing oscillation by including a current limiting resistor at an output terminal of the operational amplifier.

25. The method of claim 20 further comprising filtering out alternating current interference frequencies from the detection signal.

26. The method of claim 20 further comprising amplifying the detection signal.

27. The method of claim 20 further comprising filtering out changes in DC voltage levels from the detection signal while passing transient portions thereof.

28. The method of claim 20 further comprising buffering an impedance mismatch between the antenna and the detector circuit with an operational amplifier operated as a unity gain follower.