Tracking a position of a motorized window treatment

1. A motorized window treatment system comprising:

a covering material;

a sensor circuit configured to generate one or more sensor signals indicative of a position of the covering material; and

a control circuit configured to be powered from a supply voltage and to control a motor drive circuit, the control circuit configured to determine a present sensor state of the sensor circuit in response to the sensor signal and update a present position of the covering material in response to changes in the present sensor state of the sensor circuit;

wherein, when powering up, the control circuit configured to:

determine a power-up sensor state based on the present sensor state of the sensor circuit;

determine a predicted sensor state for the sensor circuit based at least in part on a power-down position recorded at a first time and a final position recorded at a second time;

compare the predicted sensor state with the power-up sensor state; and

update the present position of the covering material based on the comparison of the predicted sensor state and the power-up sensor state.

2. The motorized window treatment system of claim 1 , wherein, prior to determining the power-up sensor state, the control circuit is configured to:

detect a power-loss event based on a voltage falling below a predetermined low-voltage threshold;

store the present position as the power-down position based on detection of the power-loss event; and

store the present sensor state as a power-down state based on detection of the power-loss event,

wherein the predetermined low-voltage threshold is below at least one of a bus voltage and a supply voltage and is above a voltage at which the control circuit is unpowered.

3. The motorized window treatment system of claim 2 , wherein the supply voltage powers the control circuit.

4. The motorized window treatment system of claim 2 , further comprising a motor drive circuit configured to generate signals that cause a motor to change the position of the covering material, wherein the motor drive circuit is configured to receive the bus voltage for driving the motor.

5. The motorized window treatment system of claim 2 , wherein the control circuit is configured to determine the final position of the covering material prior to an end of the power-loss event.

6. The motorized window treatment system of claim 5 , wherein the control circuit is configured to update the present position of the covering material by setting the present position of the covering material equal to the final position and adjusting the present position of the covering material by an adjustment factor if the predicted sensor state is not the same as the power-up sensor state.

7. The motorized window treatment system of claim 6 , wherein the control circuit is configured to determine the adjustment factor by calculating the predicted sensor state based on a difference between the final position of the covering material and the power-down position and comparing the predicted sensor state and the power-up sensor state.

8. The motorized window treatment system of claim 6 , wherein the control circuit is configured to adjust the present position of the covering material by the adjustment factor by incrementing or decrementing the present position of the covering material depending upon a direction of rotation of a motor prior to the power-loss event.

9. The motorized window treatment system of claim 5 , wherein the control circuit is configured to adjust the present position of the covering material by setting the present position of the covering material equal to the final position if the predicted sensor state is the same as the power-up sensor state.

10. The motorized window treatment system of claim 5 , wherein the control circuit is configured to determine a predicted sensor state by setting the predicted sensor state equal to the power-down state if the final position of the covering material is equal to the power-down position.

11. The motorized window treatment system of claim 5 , wherein the control circuit is configured to determine the predicted sensor state by determining the predicted sensor state based on the power-down state and a difference between the final position of the covering material and the power-down position.

12. The motorized window treatment system of claim 1 , wherein the control circuit is configured to store an error condition in memory if the predicted sensor state is not the same as the power-up sensor state for multiple sensor signals generated by the sensor circuit.

13. A method of adjusting a present position of a covering material of a motorized window treatment, the method comprising:

determining a power-up sensor state based on a present sensor state of a sensor circuit;

determining a predicted sensor state for the sensor circuit based at least in part on a power-down position recorded at a first time and a final position recorded at a second time;

comparing the predicted sensor state with the power-up sensor state; and

determining a present position of the covering material based on the comparison of the predicted sensor state and the power-up sensor state.

14. The method of claim 13 , further comprising, prior to determining the power-up sensor state:

detecting a power-loss event based on a voltage falling below a predetermined low-voltage threshold;

storing the present position as a power-down position based on detection of the power-loss event; and

storing the present sensor state as a power-down state based on detection of the power-loss event,

wherein the predetermined low-voltage threshold is below at least one of a bus voltage and a supply voltage and is above a voltage at which a control circuit is unpowered.

15. The method of claim 14 , further comprising:

determining a final position of the covering material prior to an end of the power-loss event.

16. The method of claim 15 , wherein determining the present position of the covering material further comprises:

setting the present position of the covering material equal to the final position; and

adjusting the present position of the covering material by an adjustment factor if the predicted sensor state is not the same as the power-up sensor state.

17. The method of claim 16 , further comprising:

determining the adjustment factor by calculating the predicted sensor state based on a difference between the final position of the covering material and the power-down position and comparing the predicted sensor state and the power-up sensor state.

18. The method of claim 17 , wherein adjusting the present position of the covering material by the adjustment factor further comprises incrementing or decrementing the present position of the covering material depending upon a direction of rotation of a motor prior to the power-loss event.

19. The method of claim 15 , wherein determining the present position of the covering material further comprises setting the present position of the covering material equal to the final position if the predicted sensor state is the same as the power-up sensor state.

20. The method of claim 15 , wherein determining the predicted sensor state further comprises setting the predicted sensor state equal to the power-down state if the final position of the covering material is equal to the power-down position.

21. The method of claim 15 , wherein determining the predicted sensor state further comprises determining the predicted sensor state based on the power-down state and a difference between the final position of the covering material and the power-down position.

22. The method of claim 13 , further comprising:

storing an error condition in memory if the predicted sensor state is not the same as the power-up sensor state for multiple sensor signals generated by the sensor circuit.

23. The method of claim 14 , wherein the supply voltage powers the control circuit, and wherein a motor drive circuit is configured to receive the bus voltage for driving a motor.