Sensor or capacitance measuring with a microprocessor

• US 20060006883A1
• Filed: 06/21/2005
• Published: 01/12/2006
• Est. Priority Date: 06/25/2004
• Status: Active Grant

• Current Assignee: Kele Incorporated
• Original Assignee: Kele Incorporated
• Inventors: Foote, Steve R.
• Granted Patent: US 7,472,028 B2
• Time in Patent Office: Days
• US Class Current: 324/678
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01L 9/12 by making use of variations in capacitance , i.e. electric circuits therefor
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03K 17/955 using a capacitive detector

Abstract

An apparatus, system, or method for measuring parameters, measuring or determining capacitance, producing a digital output that is dependent upon a capacitance, or converting a variable capacitance output, of a sensor capacitor for example, into a digital format. By activating and deactivating pins, a microprocessor may form various circuits, for instance, each containing a resistor and a different capacitor, in some embodiments, without the use of intermediate switching components. The microprocessor may alternately measure the time to change the charge of each of the capacitors and then calculate the capacitance of one of the capacitors using the measured times and known capacitances of one or more reference capacitors. Certain embodiments use two reference capacitors and alternately charge and discharge the capacitors, and a simple formula may be used to calculate capacitance using times to reach a threshold voltage. A measured parameter may be humidity or pressure, for example.

Claims

1. An apparatus for measuring a parameter, the apparatus comprising:

a microprocessor having a plurality of pins;

a sensor capacitor configured to change capacitance as the parameter changes, the sensor capacitor having a first lead electrically connected to a first pin of the microprocessor, and a second lead electrically connected to a second pin of the microprocessor;

a first reference capacitor having a first lead electrically connected to a third pin of the microprocessor, and a second lead electrically connected to the second pin of the microprocessor;

a resistor having a first lead electrically connected to a fourth pin of the microprocessor, and a second lead electrically connected to the second pin of the microprocessor; and

a second reference capacitor having a first lead electrically connected to a fifth pin of the microprocessor, and a second lead electrically connected to the second pin of the microprocessor.

2. The apparatus of claim 1 wherein the parameter is a measure of the relative presence of a substance.

3. The apparatus of claim 1 wherein the parameter comprises humidity.

4. The apparatus of claim 1 wherein the parameter comprises pressure.

5. The apparatus of claim 1 wherein the parameter comprises force.

6. The apparatus of claim 1 wherein the parameter comprises acceleration.

7. The apparatus of claim 1 wherein the parameter comprises at least one of proximity and displacement.

8. The apparatus of claim 1 further comprising a comparator configured to detect whether a threshold voltage has been reached.

9. The apparatus of claim 8 further comprising a timer, wherein the apparatus is configured to use the timer to measure how long it takes for:

the sensor capacitor to reach the threshold voltage;

the first reference capacitor to reach the threshold voltage; and

the second reference capacitor to reach the threshold voltage.

10. The apparatus of claim 9 wherein the sensor capacitance is calculated using the formula:

Sensor Capacitance=[(TimerS−

Timer1)/(Timer2−

Timer1)](Ref2−

Ref1)+Ref1

wherein;

TimerS is the time for the sensor capacitor to reach the threshold voltage,

Timer1 is the time for the first reference capacitor to reach the threshold voltage,

Timer2 is the time for the second reference capacitor to reach the threshold voltage,

Ref1 is the capacitance of the first reference capacitor, and

Ref2 is the capacitance of the second reference capacitor.

11. The apparatus of claim 1 further comprising software configured to control the microprocessor so that at least the first pin, the third pin, and the fifth pin are alternately activated and when not activated, are left in a high-impedance state.

12. The apparatus of claim 1 further comprising software configured to control the microprocessor so that at least the first pin, the third pin, and the fifth pin are alternately activated and when activated, are driven as outputs to one of a first voltage and a second voltage.

13. The apparatus of claim 1 further comprising software configured to control the microprocessor so that the second pin is alternately activated as an output and as an input to a comparator, and when activated as an output, is driven to one of a first voltage and a second voltage.

14. A method of measuring the capacitance of a first capacitor, the method comprising in any order except where order is indicated, at least the steps of:

activating at least a first pin of a microprocessor, wherein the first pin is electrically connected to the first capacitor;

while the first pin is activated, measuring a time to change the charge of the first capacitor;

after the measuring of the time to change the charge of the first capacitor, deactivating the first pin into a high impedance state;

activating at least a second pin of the microprocessor, wherein the second pin is electrically connected to a second capacitor;

while the second pin is activated, measuring a time to change the charge of the second capacitor;

after the measuring of the time to change the charge of the second capacitor, deactivating the second pin into a high impedance state;

activating at least a third pin of the microprocessor, wherein the third pin is electrically connected to a third capacitor;

while the third pin is activated, measuring a time to change the charge of the third capacitor;

after the measuring of the time to change the charge of the third capacitor, deactivating the third pin into a high impedance state;

using at least the time to change the charge of the first capacitor, the time to change the charge of the second capacitor, and the time to change the charge of the third capacitor, calculating the capacitance of the first capacitor.

15. The method of claim 14 wherein the second capacitor and third capacitor are reference capacitors having known capacitances and the step of calculating the capacitance of the first capacitor includes finding the difference in capacitance between the second capacitor and the third capacitor.

16. The method of claim 14 wherein the second capacitor and third capacitor are reference capacitors having known capacitances and the step of calculating the capacitance of the first capacitor includes adding the capacitance of the second capacitor.

17. The method of claim 14 wherein the step of calculating the capacitance of the first capacitor includes finding the difference between the time to change the charge of the first capacitor and the time to change the charge of the second capacitor.

18. The method of claim 14 wherein the step of calculating the capacitance of the first capacitor includes finding the difference between the time to change the charge of the second capacitor and the time to change the charge of the third capacitor.

19. The method of claim 14 wherein the step of calculating the capacitance of the first capacitor includes finding the difference between the time to change the charge of the first capacitor and the time to change the charge of the second capacitor, and dividing this quantity by the difference between the time to change the charge of the second capacitor and the time to change the charge of the third capacitor.

20. The method of claim 14 wherein the step of calculating the capacitance of the first capacitor comprises using the formula:

Sensor Capacitance=[(TimerS−

Timer1)/(Timer2−

Timer1)](Ref2−

Ref1)+Ref1

wherein;

TimerS is the time to change the charge of the first capacitor,

Timer1 is the time to change the charge of the second capacitor,

Timer2 is the time to change the charge of the third capacitor,

Ref1 is the capacitance of the second capacitor, and

Ref2 is the capacitance of the third capacitor.

21. The method of claim 14 wherein the step of measuring of the time to change the charge of the first capacitor includes detecting when a threshold voltage is reached and measuring the time to reach the threshold voltage.

22. The method of claim 14 wherein the steps of measuring a time to change the charge of the first capacitor, measuring a time to change the charge of the second capacitor, and measuring a time to change the charge of the third capacitor are repeated, in any order, alternating between charging and discharging the first, second, and third capacitors.

23. An apparatus for determining the capacitance of a sensor capacitor, the apparatus comprising:

a first reference capacitor;

a voltage comparator;

a timer; and

a microprocessor comprising;

a first pin electrically connected to the sensor capacitor, wherein the microprocessor is configured to activate the first pin as an output and drive the first pin to a first voltage, the microprocessor is configured to activate the first pin as an output and drive the first pin to a second voltage, and the microprocessor is configured to deactivate the first pin into a high-impedance state,

a second pin electrically connected to the first reference capacitor, wherein the microprocessor is configured to activate the second pin as an output and drive the second pin to the first voltage, the microprocessor is configured to activate the second pin as an output and drive the second pin to the second voltage, and the microprocessor is configured to deactivate the second pin into a high-impedance state,

at least one third pin electrically connected to at least one of the sensor capacitor and the first reference capacitor, wherein the microprocessor is configured to activate at least one third pin as an output and drive the at least one third pin to the first voltage, the microprocessor is configured to activate at least one third pin as an output and drive the at least one third pin to the second voltage, and the microprocessor is configured to activate at least one third pin as an input to the comparator;

wherein the microprocessor is configured to use the timer to measure a first time for the sensor capacitor to change from the first voltage to a first threshold voltage, the microprocessor is configured to use the timer to measure a second time for the first reference capacitor to change from the first voltage to the first threshold voltage, and the microprocessor is configured to use at least the first time, the second time, and a capacitance of the first reference capacitor to calculate a capacitance of the sensor capacitor.

24. The apparatus of claim 23 wherein the first threshold voltage is between the first voltage and the second voltage.

25. The apparatus of claim 23 further comprising a second reference capacitor, wherein the microprocessor further comprises a fourth pin electrically connected to the second reference capacitor, wherein the microprocessor is configured to activate the fourth pin as an output and drive the fourth pin to the first voltage, the microprocessor is configured to activate the fourth pin as an output and drive the second pin to the second voltage, the microprocessor is configured to deactivate the fourth pin into a high-impedance state, the microprocessor is configured to use the timer to measure a third time for the second reference capacitor to change from the first voltage to the first threshold voltage, and the microprocessor is configured to use at least the first time, the second time, the third time, a capacitance of the first reference capacitor, and the capacitance of the second reference capacitor to calculate the capacitance of the sensor capacitor.

26. The apparatus of claim 23 wherein the microprocessor is configured to use the timer to measure a fourth time for the sensor capacitor to change from the second voltage to a second threshold voltage, the microprocessor is configured to use the timer to measure a fifth time for the first reference capacitor to change from the second voltage to the second threshold voltage, and the microprocessor is configured to use at least the fourth time, the fifth time, and the capacitance of the first reference capacitor to calculate the capacitance of the sensor capacitor.

27. The apparatus of claim 23 further comprising a resistor, wherein the microprocessor further comprises a fifth pin electrically connected to the resistor, wherein the microprocessor is configured to drive the fifth pin to the first voltage, the microprocessor is configured to drive the fifth pin to the second voltage, and the microprocessor is configured to pass electrical current through the resistor when measuring at least the first time and the second time.

28. An apparatus for producing a digital output that is dependent upon a capacitance of a sensor capacitor, the apparatus comprising:

a microprocessor having a plurality of pins;

a sensor capacitor having a first lead electrically connected to a first pin of the microprocessor, and a second lead electrically connected to at least one common pin of the microprocessor;

a first reference capacitor having a first lead electrically connected to a second pin of the microprocessor, and a second lead electrically connected to at least one common pin of the microprocessor; and

a resistor having a first lead electrically connected to a third pin of the microprocessor, and a second lead electrically connected to at least one common pin of the microprocessor; and

wherein the microprocessor is configured to;

activate the first pin and at least one common pin as voltage outputs to apply a first voltage across the sensor capacitor;

activate the third pin as a voltage output to establish a first current through the resistor;

deactivate at least one common pin as a voltage output;

activate at least one common pin as a comparator input;

measure the time for a voltage across the sensor capacitor to reach a threshold voltage using the comparator input;

deactivate the first pin to a high-impedance state;

activate the second pin and at least one common pin as voltage outputs to apply the first voltage across the first reference capacitor;

activate the third pin as a voltage output to establish the first current through the resistor;

deactivate at least one common pin as a voltage output;

activate at least one common pin as a comparator input;

measure the time for the voltage across the first reference capacitor to reach the threshold voltage using the comparator input;

deactivate the second pin to a high-impedance state; and

calculate a digital output that is dependent upon the capacitance of the sensor capacitor using at least the time for the voltage across the sensor capacitor to reach the threshold voltage and the time for the voltage across the first reference capacitor to reach the threshold voltage.

29. The apparatus of claim 28 further comprising

a second reference capacitor having a first lead electrically connected to a fourth pin of the microprocessor, and a second lead electrically connected to at least one common pin of the microprocessor;

wherein the microprocessor is further configured to;

activate the fourth pin and at least one common pin as voltage outputs to apply the first voltage across the second reference capacitor;

activate the third pin as a voltage output to establish a first current through the resistor;

deactivate at least one common pin as a voltage output;

activate at least one common pin as a comparator input;

measure the time for the voltage across the second reference capacitor to reach the threshold voltage using the comparator input;

deactivate the fourth pin to a high-impedance state; and

calculate the digital output that is dependent upon the capacitance of the sensor capacitor using at least the time for the voltage across the sensor capacitor to reach the threshold voltage, the time for the voltage across the first reference capacitor to reach the threshold voltage, and the time for the voltage across the second reference capacitor to reach the threshold voltage.

30. A method of converting the variable capacitance output of a sensor capacitor into a digital format, the method comprising in any order at least the steps of:

using a microprocessor, without the use of intermediate switching components, forming a circuit to facilitate changing the charge of the sensor capacitor;

using the microprocessor, without the use of intermediate switching components, changing the charge of the sensor capacitor while measuring the time required to change the charge of the sensor capacitor;

using the microprocessor, without the use of intermediate switching components, reconfiguring the circuit to facilitate changing the charge of a first reference capacitor;

using the microprocessor, without the use of intermediate switching components, changing the charge of the first reference capacitor while measuring the time required to change the charge of the first reference capacitor;

using the microprocessor, without the use of intermediate switching components, reconfiguring the circuit to facilitate changing the charge of a second reference capacitor;

using the microprocessor, without the use of intermediate switching components, changing the charge of the second reference capacitor while measuring the time required to change the charge of the second reference capacitor; and

using the microprocessor and at least the time required to change the charge of the sensor capacitor, the time required to change the charge of the first reference capacitor, and the time required to change the charge of the second reference capacitor, calculating a digital output that is dependent upon the capacitance of the sensor capacitor.

31. The method of claim 30 wherein the steps of changing the charge of the sensor capacitor, changing the charge of the first reference capacitor, and changing the charge of the second reference capacitor are all accomplished by passing current through a common resistor electrically connected to the microprocessor without any intermediate switching components there between.

32. The method of claim 30 wherein the steps of changing the charge of the sensor capacitor, changing the charge of the first reference capacitor, and changing the charge of the second reference capacitor are all accomplished by changing the charge from a common first voltage to a common threshold voltage.

33. The method of claim 30 wherein the changing the charge of the sensor capacitor and the changing the charge of the first reference capacitor are repeated, alternating between changing from a lower potential to a higher potential, and changing from a higher potential to a lower potential.

34. The method of claim 30 wherein the step of calculating a digital output comprises using the formula:

Sensor Capacitance=[(TimerS−

Timer1)/(Timer2−

Timer1)](Ref2−

Ref1)+Ref1

wherein;

TimerS is the time to change the charge of the sensor capacitor,

Timer1 is the time to change the charge of the first reference capacitor,

Timer2 is the time to change the charge of the second reference capacitor,

Ref1 is the capacitance of the first reference capacitor, and

Ref2 is the capacitance of the second reference capacitor.