Apparatus and method for determining the attitude of a remotely monitored device

1. An attitude detector for determining a horizontal resting orientation or a non-horizontal orientation of a monitoring device, the monitoring device is associated with a tracked person, the detector comprising:

a first tip-over switch of a first operating angle; and a second tip-over switch of a second operating angle, said second operating angle is larger than said first operation operating angle, wherein said first and second tip-over switches are coupled to said monitoring device such that a change in orientation of the monitoring device causes an equivalent change in orientation of both said first and second tip-over switches and wherein each of said first and second tip-over switches gives an output signal of a first value when tilted by an angle above its respective operating angle and of a second value when tilted by an angle below its respective operating angle;

a tip-over transition counter for counting transitions of said first tip-over switch during a predetermined time interval; and

an attitude calculator module configured to receive readouts of said tip-over transition counter and said second tip-over switch, to calculate a tip-over counter value according to said readouts, and to determine the orientation of said monitoring device based on said tip-over counter value and a set of pre-loaded parameters.

2. The detector of claim 1 wherein the first operating angle is in the range of from about 5 degrees to about 14 degrees.

3. The detector of claim 1 wherein the first operating angle is of about 5 degrees.

4. The detector of claim 1 wherein the first operating angle is of about 7 degrees.

5. The detector of claim 1 wherein the second operating angle is in the range of from about 15 degrees to about 30 degrees.

6. The detector of claim 1 wherein the second operating angle is of about 25 degrees.

7. The detector of claim 1 wherein the second operating angle is of about 23 degrees.

8. The detector of claim 1 wherein said pre-loaded set of parameters includes a transition counter threshold, a high transition limit, a low transition limit, a maximum counting limit and a minimum counting limit.

9. The detector of claim 1 wherein the monitoring unit comprises a location unit and wherein said location unit is inactivated upon determination of a horizontal resting orientation and re-activated upon determination of a non-horizontal orientation.

10. The detector according to claim 9 wherein said location unit is a GPS receiver.

11. A monitoring device associated with a tracked person, the monitoring device comprising:

a GPS receiver for receiving location coordinates of said monitoring device;

an attitude detector for detecting a horizontal/non-horizontal orientation of said monitoring device, and

a control circuit adapted for activating said GPS receiver when the orientation of said device is determined to be non-horizontal and for inactivating said GPS receiver when the orientation is determined to be horizontal

wherein the attitude detector comprises:

a first tip-over switch of a first operating angle and a second tip-over switch of a second operating angle, said second operating angle being larger than said first operating angle, wherein both the first and second tip-over switches are coupled to said monitoring device such that a change in orientation of the monitoring device causes an equivalent change in orientation both said first and second tip-over switches and wherein each of said first and second tip-over gives an output signal of a first value when tilted by an angle above its respective operating angle and of a second value when tilted by an angle below its respective operating angle;

a tip-over transition counter for counting transition of said first tip-over switch during

a predetermined time interval; and

an attitude calculator module to receive readouts of said tip-over transition counter and said second tip-over switch, to calculate a tip-over counter value according to said readouts, and to determine the orientation of said monitoring device based on said tip-over counter value and a stored set of predetermined parameters.

12. The monitoring device of claim 11 wherein said device is in short-range wireless communication with an electronic tag worn by the monitored person.

13. The monitoring device of claim 12 wherein said device further includes a communications means for communicating with a central monitoring device.

14. A method for determining a horizontal/non-horizontal orientation of a monitoring device, the monitoring device is associated with a tracked person, the method comprising:

providing said monitoring device with a first tip-over switch of a first operating angle and a second tip-over switch of a second operating angle such that a change in orientation of the monitoring device causes an equivalent change in orientation of both said first and second tip-over switches, said second operating angle is larger than said first operating angle and each of said first and second tip-over switches output a signal of a first value when tilted by an angle above its respective operating angle and of a second value when tilted by an angle below its respective operating angle; counting transitions of said first tip-over switch during a pre-defined time interval to obtain a first tip-over transitions number;

calculating a tip-over counter value based on (i) a last stored tip-over counter value, (ii) said first tip-over transitions number; and (iii) the output signal of the second tip-over switch; and

determining the orientation of said device by comparing said tip-over counter value to a set of pre-loaded parameters.

15. The method of claim 14 wherein said pre-defined time interval is in the range of 1 to 2 seconds.

16. The method of claim 14 wherein the first operating angle is in the range of from about 5 degrees to about 14 degrees.

17. The method of claim 14 wherein the second operating angle is in the range of from about 15 degrees to about 30 degrees.

18. The method of claim 14 wherein said monitoring device includes a location unit and wherein the method further comprises a step of activating or inactivating said location unit upon detection of a transition from horizontal to non-horizontal orientation or from non-horizontal to horizontal orientation, respectively.