Micropower differential sensor measurement

A sensing device includes a Wheatstone bridge and a source of a stimulation configured to apply the stimulation across two electrodes of the Wheatstone bridge. The device also includes a timing sensitive circuit configured to detect timing of a signal appearing across one of the other electrodes of the bridge as a result of the stimulation being applied. The timing provides a way to read the sensor. The device can be powered remotely and data so read can be transmitted using the remote power. The timing sensitive circuit includes a comparator. The comparator provides a high logic signal for a time related to the reactance of one leg of the Wheatstone bridge, and that provides a reading of a differential sensor having elements in each leg of the bridge.

What is claimed is:

1. An electronic circuit, comprising:

a first electrode, a second electrode, a third electrode and a fourth electrode;

a sensor comprising a first variable element connected to a second variable element at said first electrode, said first variable element also connected to said second electrode, said second variable element also connected to said third electrode;

a first device connected between said second electrode and said fourth electrode;

a second device connected between said third electrode and said fourth electrode;

a source of a stimulation connected to apply a time varying stimulation across said first and said fourth electrodes; and

a timing sensitive circuit configured to measure duration of a signal appearing between said second electrode and said third electrode that arises from said stimulation applied across said first and fourth electrodes.

2. The electronic device as recited in claim 1, wherein said first variable element comprises a variable capacitor, a variable inductor, or a variable resistor.

3. The electronic device as recited in claim 2, further comprising a Wheatstone bridge wherein said Wheatstone bridge comprises a first leg and a second leg, said first leg comprising said first variable element, said second electrode, said first device, and said fourth electrode, said second leg comprising said first electrode, said second variable element, said third electrode, said second device, and said fourth electrode.

4. The electronic device as recited in claim 3, wherein said first variable element is connected between said first electrode and said second electrode, said first device is connected between said second electrode and said fourth electrode, said second variable element is connected between said first electrode and said third electrode, and said second device is connected between said third electrode and said fourth electrode.

5. The electronic device as recited in claim 4, wherein said Wheatstone bridge comprises a pair of variable capacitors or a pair of variable inductors wherein a first capacitor of said pair of capacitors or a first inductor of said pair of inductors is in said first leg and a second capacitor of said pair of capacitors or a second inductor of said pair of inductors is in said second leg.

6. The electronic device as recited in claim 5, wherein said first and second devices comprise a pair of fixed matched resistors, wherein a first resistor of said pair of matched resistors is in said first leg and a second resistor of said pair of matched resistors is in said second leg.

7. The electronic device as recited in claim 4, wherein said first and second variable elements comprise a pair of variable resistors, wherein a first variable resistor of said pair of variable resistors is in said first leg and a second variable resistor of said pair of variable resistors is in said second leg.

8. The electronic device as recited in claim 7, wherein said Wheatstone bridge further comprises a pair of fixed matched capacitors or a pair of fixed matched inductors wherein a first capacitor of said pair of fixed matched capacitors or a first inductor of said pair of fixed matched inductors is in said first leg and a second capacitor of said pair of fixed matched capacitors or a second inductor of said pair of fixed matched inductors is in said second leg.

9. The electronic device as recited in claim 1, wherein said source of said time varying stimulation comprises a pulse generator.

10. The electronic device as recited in claim 9, wherein said pulse generator comprises a microprocessor controlled by software.

11. The electronic device as recited in claim 9, wherein said pulse generator comprises a discrete pulse generator.

12. The electronic device as recited in claim 9, wherein said time varying stimulation comprises a leading edge, wherein said leading edge sets said timing sensitive circuit.

13. The electronic device as recited in claim 1, wherein said timing sensitive circuit is sensitive to a reactive time constant of a signal traveling in said first variable element and said first device.

14. The electronic device as recited in claim 13, wherein said first variable element and said first device comprise a first time delay, wherein said second variable element and said second device comprise a second time delay, wherein said first time delay is larger than said second time delay by an amount, and wherein said timing sensitive circuit measures a timing related to said amount.

15. The electronic device as recited in claim 14, wherein said timing sensitive circuit further comprises a comparator.

16. The electronic device as recited in claim 15, wherein said comparator is configured to provide magnitude of change of said sensor from said timing.

17. The electronic device as recited in claim 16, wherein said comparator outputs a square pulse signal, wherein said signal lasts for a time proportional to said reactive time constant of said first leg of said Wheatstone bridge.

18. The electronic device as recited in claim 15, wherein said timing sensitive circuit comprises a pair of comparators.

19. The electronic device as recited in claim 18, wherein said pair of comparators are configured to provide both direction and magnitude of change of said sensor elements.

20. The electronic device as recited in claim 18, wherein said pair of comparators are configured as a set-reset latch.

21. The electronic device as recited in claim 1, wherein said timing sensitive circuit measures analog position of said first variable element.

22. The electronic device as recited in claim 15, further comprising a circuit for reading timing information from said comparator and providing a signal with data from said comparator encoded for external transmission.

23. The electronic device as recited in claim 22, wherein said signal for external transmission is provided to a coil for external transmission.

24. The electronic device as recited in claim 22, wherein said signal for external transmission is used to modulate a radio transmitter carrier wave for radio transmission to a remote radio receiver.

25. The electronic device as recited in claim 24, further comprising a receive coil to wirelessly receive power wherein power received by said receive coil also supplies power to said radio transmitter.

26. The electronic device as recited in claim 22, wherein said data further comprises address information identifying the electronic device transmitting data.

27. The electronic device as recited in claim 1, further comprising a remote power source for powering the electronic device.

28. The electronic device as recited in claim 27, wherein said remote power source comprises a source of electromagnetic radiation directed at a receive coil connected to a rectifier in the electronic device.

29. The electronic device as recited in claim 28, wherein said rectifier is connected to said source of stimulation and to said timing sensitive circuit to provide power for their operation.

30. The electronic device as recited in claim 28, wherein said remote power source further comprises a coil for receiving information from the electronic device.

31. The electronic device as recited in claim 1, wherein said sensor is a peak strain detection linear displacement sensor.

32. The electronic device as recited in claim 1, further comprising a plurality of said sensors and an ID generator, said ID generator to identify which of said sensors is being interrogated.

33. A method of reading a sensor comprising the steps of:

(a) providing a differential sensor having a first variable element and a second variable element;

(b) providing a first comparator; and

(c) providing a time varying signal to said first variable element and to said second variable element wherein said sensor produces an output depending on magnitude of a difference between said first variable element and said second variable element, and using said first comparator for providing a signal having a time duration that is a measure of said magnitude.

34. The method as recited in claim 33, wherein said first variable element is a resistor, a capacitor or an inductor and said magnitude is a resistance, capacitance, or inductance.

35. The method as recited in claim 33, wherein a second comparator is connected to said second variable element.

36. The method as recited in claim 33, wherein said signal comprises a pulse.

37. The method as recited in claim 33, wherein a single pulse is sufficient to read said sensor.

38. The method as recited in claim 33, wherein said sensor comprises a reactive element and a resistive element, wherein said output depends on a time constant of said reactive and said resistive elements.

39. The device as recited in claim 1, wherein said a first variable element or said first device is reactive.

40. The device as recited in claim 39, wherein said a second variable element or said second device is reactive.

41. The method as recited in claim 33, wherein said providing step (b) comprises connecting said first comparator to said first variable element and to said second variable element.

42. The method as recited in claim 41, further comprising the step of providing a second comparator, wherein said second comparator is connected to said first variable element and to said second variable element.

43. The method as recited in claim 42, wherein said first comparator comprises a plus input connected to said first variable element and said second comparator comprises a plus input connected to said second variable element and wherein said first comparator comprises a minus input connected to said second variable element and said second comparator comprises a minus input connected to said first variable element.

44. The method as recited in claim 33, wherein said first comparator comprises a first plus input, a first minus input, and a first output, wherein said first plus input is connected to said first variable element and wherein said second comparator comprises a second plus input, a second minus input, and a second output, wherein said second plus input is connected to said second variable element, and wherein said first minus input is connected to said second output and said second minus input is connected to said first output to provide a latch.

45. An electronic circuit comprising a Wheatstone bridge, a detection circuit, and a signal generator, said Wheatstone bridge comprising first, second, third, and fourth electrodes, said signal generator for providing a time varying signal across said first and fourth electrodes, wherein said detection circuit is connected across said second and third electrodes, wherein said detection circuit has an output having a time duration proportional to magnitude of unbalance of said Wheatstone bridge.

46. The electronic device as recited in claim 45, wherein said signal generator is set to provide a pulse.

47. The electronic device as recited in claim 46, wherein said detection circuit provides a non-zero output in response to said pulse for a time proportional to said magnitude of unbalance of said Wheatstone bridge.

48. The electronic device as recited in claim 46, wherein said Wheatstone bridge comprises at least one reactive element.

49. The electronic device as recited in claim 48, wherein said Wheatstone bridge comprises at least one resistive element along with said at least one reactive element.

50. The electronic device as recited in claim 46, wherein said Wheatstone bridge comprises at least one variable element.

51. The electronic device as recited in claim 50, wherein said Wheatstone bridge comprises at least one variable reactive element.

52. The electronic device as recited in claim 46, wherein said Wheatstone bridge comprises two variable reactive elements to provide a differential sensor.

53. The electronic device as recited in claim 52, wherein said Wheatstone bridge further comprises two fixed elements.

54. The electronic device as recited in claim 53, wherein said detection circuit comprises a comparator.