Differential pest sensor

1. A pest sensor comprising a processor configured to:

receive a first signal indicative of a first impedance across a first sensing circuit;

receive a second signal indicative of a second impedance across a second sensing circuit; and

in response to detecting that one of the first or second signals differs from the other by more than a predefined difference threshold, output an indication of pest activity.

2. The pest sensor of claim 1 wherein the indication of pest activity is output in response to detecting that the one of the first or second signals differs from the other by more than the predefined difference threshold for more than a predetermined period of time or for more than a predetermined number of consecutive measurements.

3. The pest sensor of claim 1 wherein the processor is configured to, in response to detecting that the one of the first or second signals differs from the other by more than the predefined difference threshold, enter a triggered state and remain in the state until receiving an instruction to reset.

4. The pest sensor of claim 1 wherein the indication of pest activity is output via a wireless interface to notify a central monitoring system and/or wherein the indication of pest activity is output via an indicator on the pest sensor.

5. The pest sensor of claim 1 wherein the processor is configured to, in response to detecting that both the first impedance and the second impedance are below the predefined threshold, output an indication that the first and second sensing circuits have been compromised by a short circuit.

6. The pest sensor of claim 1 wherein the processor is configured to output an indication that the first and second sensing circuits have been disconnected or broken in response to both the first impedance and the second impedance being greater than a further predefined threshold that is greater than the predefined threshold.

7. The pest sensor of claim 1 comprising circuitry for obtaining the first and second signals, the circuitry comprising a set of electrodes for connecting to first and second tracks of the first sensing circuit and to first and second tracks of the second sensing circuit, wherein the pest sensor is configured to measure the first signal across the first and second tracks of the first sensing circuit and to measure the second signal across the first and second tracks of the second sensing circuit.

8. The pest sensor of claim 7 wherein the set of electrodes comprise a shared electrode or a shared set of electrodes for connecting to the second tracks of the second tracks of the first and second sensing circuits wherein the second tracks are connected as a shared second track.

9. The pest sensor of claim 7 wherein:

the pest sensor comprises biasing circuitry configured to apply a voltage to the first tracks of the first and second sensing circuits, and to connect the second tracks of the first and second sensing circuits to ground; or

the pest sensor comprises biasing circuitry configured to apply a voltage to the second tracks of the first and second sensing circuitry, and to connect the first tracks of the first and second sensing circuits to ground.

10. The pest sensor of claim 1 further configured to releasably connect to the first and second sensing circuits.

11. The pest sensor of claim 1 wherein the first and second sensing circuits form part of a detector and wherein the pest sensor comprises a breakage sensor configured to connect to a pair of connected electrodes on the detector and to detect when the detector has been disconnected or broken in response to an increase in the loop resistance measured at the pair of connected electrodes.

12. A detector for use in a pest sensing system, the detector comprising first and second sensing circuits, each comprising:

a first electrode connected to a first track running along a longitudinal direction;

a second electrode connected to a second track running substantially parallel to the first track; and

sensing tracks in the form of a set of fingers located between the first and second tracks, a first set of the fingers being connected to the first track only and reaching towards the second track, and a second set of the fingers being connected to the second track only and reaching towards the first track, the first and second sets of fingers being interdigitated with each other and separated from each other such that pest activity can be detected via a reduction in the impedance between the two sets of interdigitated fingers, measured via the first and second electrodes, wherein at least a portion of each finger runs in a direction that has at least some component that is in the longitudinal direction.

13. The detector of claim 12 wherein the interdigitated fingers have complimentary zig-zag patterns running substantially along the transverse direction and providing alternating positive and negative longitudinal components.

14. The detector of claim 12 comprising a set of channels formed over at least one of the first and second sensing circuits and running along the transverse direction to direct pests to pass over the at least one of the first and second sensing circuits.

15. The detector of claim 12 wherein the second track of the first sensing circuit is connected to the second track of the second sensing circuit to form a combined central track running along the longitudinal direction.

16. The detector of claim 12 further comprising a breakage detection circuit comprising one or more conductive loops connected between a pair of electrodes such that breakage or disconnection of the detector can be detected via a change in loop resistance measured across the pair of electrodes.

17. The detector of claim 16 wherein the breakage detection circuit comprises a plurality of conductive loops, each of a different length to the other, extending along the longitudinal direction.

18. The detector of claim 17 wherein the loops are formed by two parallel tracks running along the longitudinal direction and connected by a succession of transverse connectors located at various distances along the longitudinal direction.

19. A pest sensing system comprising a pest sensor and a detector for use in the pest sensing system, wherein:

the detector comprises first and second sensing circuits, each comprising:

a first electrode connected to a first track running along a longitudinal direction;

a second electrode connected to a second track running substantially parallel to the first track; and

sensing tracks in the form of a set of fingers located between the first and second tracks, a first set of the fingers being connected to the first track only and reaching towards the second track, and a second set of the fingers being connected to the second track only and reaching towards the first track, the first and second sets of fingers being interdigitated with each other and separated from each other such that pest activity can be detected via a reduction in the impedance between the two sets of interdigitated fingers, measured via the first and second electrodes; and

the pest sensor comprises a processor configured to:

receive a first signal indicative of a first impedance across the first sensing circuit;

receive a second signal indicative of a second impedance across the second sensing circuit; and

in response to detecting that one of the first or second signals differs from the other by more than a predefined difference threshold, output an indication of pest activity.

20. A detector for use in a pest sensing system, the detector comprising:

first and second sensing circuits, each comprising:

a first electrode connected to a first track running along a longitudinal direction;

a second electrode connected to a second track running substantially parallel to the first track; and

sensing tracks in the form of a set of fingers located between the first and second tracks, a first set of the fingers being connected to the first track only and reaching towards the second track, and a second set of the fingers being connected to the second track only and reaching towards the first track, the first and second sets of fingers being interdigitated with each other and separated from each other such that pest activity can be detected via a reduction in the impedance between the two sets of interdigitated fingers, measured via the first and second electrodes; and

a set of channels formed over at least one of the first and second sensing circuits and running along the transverse direction to direct pests to pass over the at least one of the first and second sensing circuits.

21. A detector for use in a pest sensing system, the detector comprising first and second sensing circuits, each comprising:

a first electrode connected to a first track running along a longitudinal direction;

a second electrode connected to a second track running substantially parallel to the first track; and

sensing tracks in the form of a set of fingers located between the first and second tracks, a first set of the fingers being connected to the first track only and reaching towards the second track, and a second set of the fingers being connected to the second track only and reaching towards the first track, the first and second sets of fingers being interdigitated with each other and separated from each other such that pest activity can be detected via a reduction in the impedance between,

wherein the second track of the first sensing circuit is connected to the second track of the second sensing circuit to form a combined central track running along the longitudinal direction.

22. A detector for use in a pest sensing system, the detector comprising:

first and second sensing circuits, each comprising:

a first electrode connected to a first track running along a longitudinal direction;

a second electrode connected to a second track running substantially parallel to the first track; and

sensing tracks in the form of a set of fingers located between the first and second tracks, a first set of the fingers being connected to the first track only and reaching towards the second track, and a second set of the fingers being connected to the second track only and reaching towards the first track, the first and second sets of fingers being interdigitated with each other and separated from each other such that pest activity can be detected via a reduction in the impedance between; and

a breakage detection circuit comprising one or more conductive loops connected between a pair of electrodes such that breakage or disconnection of the detector can be detected via a change in loop resistance measured across the pair of electrodes.