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A motorized window treatment may provide a low-cost solution for controlling the amount of daylight entering a space through a window. The window treatment may include a covering material (e.g., a cellular shade fabric or a roller shade fabric), a drive assembly for raising and lowering the covering

A motorized window treatment may provide a low-cost solution for controlling the amount of daylight entering a space through a window. The window treatment may include a covering material (e.g., a cellular shade fabric or a roller shade fabric), a drive assembly for raising and lowering the covering material, and a motor drive unit including a motor configured to drive the drive assembly to raise and lower the covering material. The motorized window treatment may comprise one or more battery packs configured to receive batteries for powering the motor drive unit. The batteries may be located out of view of a user of the motorized window treatment (e.g., in a headrail or in a battery compartment). The motorized window treatment may use various power-saving methods to lengthen the lifetime of the batteries, e.g., to reduce the motor speed to conserve additional battery power and extend the lifetime of the batteries.

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1. A motorized window treatment comprising: a covering material;a drive assembly configured to raise and lower the covering material;a motor drive unit including a motor configured to drive the drive assembly to raise and lower the covering material between a fully-open position and a fully-closed p

1. A motorized window treatment comprising: a covering material;a drive assembly configured to raise and lower the covering material;a motor drive unit including a motor configured to drive the drive assembly to raise and lower the covering material between a fully-open position and a fully-closed position and to any position intermediate the fully-open and fully-closed positions; andat least one battery pack configured to hold at least one battery for producing a battery voltage to power the motor drive unit;wherein the motor drive unit is configured to monitor the magnitude of the battery voltage, the motor drive unit further configured to operate the motor at a reduced motor speed in response to the state of charge being reduced below a first predetermined threshold. 2. The motorized window treatment of claim 1, wherein the motor drive unit comprises a motor and a controller configured to rotate the motor to adjust the position of the covering material. 3. The motorized window treatment of claim 2, wherein the motor drive unit further comprises a transistor-bridge drive circuit, the controller configured to provide a pulse width modulated (PWM) control signal to the drive circuit for driving the motor to control the rotational speed of the motor so as to cause the transistor-bridge drive circuit to conduct a pulse-width modulated load current. 4. The motorized window treatment of claim 3, further comprising: a filter circuit having an input electrically coupled to the battery-powered supply to receive the battery voltage, and an output electrically coupled to the transistor-bridge circuit to conduct the pulse-width modulated load current;wherein the filter circuit is configured to conduct a substantially DC battery current from the battery-powered supply. 5. The motorized window treatment of claim 3, wherein the controller is configured to ramp the rotational speed up from zero to a desired rotational speed across a ramp time when starting the motor from a stopped condition. 6. The motorized window treatment of claim 3, wherein the controller is configured to increase the duty cycle of the PWM control signal as the covering material is raised from the midway position to the fully-open position and when the covering material is lowered from the midway position to the fully-closed position. 7. The motorized window treatment of claim 3, further comprising: a power supply for receiving the battery voltage and generating a DC supply voltage having a first nominal magnitude for powering the controller;wherein the controller is configured to increase the magnitude of the DC supply voltage to a second increased magnitude greater than the first magnitude when the controller is driving the motor drive circuit to raise and lower the covering material. 8. The motorized window treatment of claim 2, wherein the motor drive unit further comprises a rotational position sensor to enable the motor drive unit to sense movement of an output shaft of the motor, the controller configured to determine the position of a bottom end of the covering material in response to the rotational position sensor. 9. The motorized window treatment of claim 8, wherein the covering material is engageable by a user to manually adjust the covering material, the controller configured to determine the position of the covering material in response to the covering material being manually adjusted. 10. The motorized window treatment of claim 9, wherein the motor produces an electromotive force when the covering material is manually adjusted, the electromotive force being coupled to an input of the controller, the controller having a sleep mode and an active mode, the controller changing from the sleep mode to the active mode in response to the controller input receiving the electromotive force and allowing the controller to receive and process a sensor signal received from the rotational position sensor to determine the position of the bottom end of the covering material if the covering material is manually adjusted. 11. The motorized window treatment of claim 8, further comprising: a supplemental power source configured to power the controller; anda memory configured to store data related to the determined position to prevent loss of the position data it the at least one battery is removed from the battery pack. 12. The motorized window treatment of claim 2, wherein the controller is configured to begin operating in a first low-battery mode in response to the magnitude of the battery voltage dropping below the first predetermined low-battery threshold, the controller configured to operate the motor at the reduced motor speed in the first low-battery mode; wherein the controller is configured to begin operating in a second low battery mode in response to the magnitude of the battery voltage dropping below the first predetermined low-battery threshold a second time, the controller configured to stop the rotation of the motor in the second low-battery mode; andwherein the controller is configured to begin operating in a third low-battery mode in response to the magnitude of the battery voltage dropping below the first predetermined low-battery threshold a third time, the controller configured to shut down in the third low-battery mode so that approximately no current is drawn from the battery-powered supply. 13. The motorized window treatment of claim 2, wherein the controller is configured to determine if the magnitude of the battery voltage is below a second predetermined threshold less than the first predetermined threshold, the motor drive unit configured to prevent movements of the covering material except to allow for one additional movement of the covering material to the fully-open position if the magnitude of the battery voltage has dropped below the second predetermined threshold. 14. The motorized window treatment of claim 1, wherein the motor drive unit is configured to prevent the motor from operating to lower the covering material until an upper limit for the covering material is reset after a loss of power. 15. The motorized window treatment of claim 1, wherein the at least one battery pack comprises first and second battery packs, each battery pack comprising a plurality of batteries electrically coupled in series. 16. The motorized window treatment of claim 15, further comprising: a battery-balancing circuit electrically coupled to the first and second battery packs;wherein a series combination of a first diode and the batteries of the first battery pack is electrically coupled in parallel with a series combination of a second diode and the batteries of the second battery pack so as to generate a battery voltage at an output of the battery-balancing circuit. 17. The motorized window treatment of claim 16, wherein the battery-balancing circuit comprises the first diode electrically coupled in series with the series-coupled batteries of the first battery pack and the second diode electrically coupled in series with the series-coupled batteries of the second battery pack, the cathodes of the first and second diodes electrically coupled together to produce the battery voltage at the junction of the first and second diodes. 18. The motorized window treatment of claim 17, wherein the junction of the first and second diodes and a common reference of the battery packs are electrically coupled to the motor drive unit via two respective electrical wires, the motorized window treatment further comprising: a wire antenna for receiving RF signals, the wire antenna extending from the motor drive unit adjacent to the electrical wires that extend between the battery packs and the motor; andat least one ferrite bead mechanically coupled around the electrical wires that extend between the battery packs and the motor and positioned adjacent the motor drive unit. 19. The motorized window treatment of claim 15, wherein the series-coupled batteries of the first battery pack are electrically coupled in series with the series-coupled batteries of the second battery pack so as to generate a battery voltage across the series combination of battery packs. 20. The motorized window treatment of claim 19, wherein the motor drive unit comprises a positive-temperature coefficient thermistor electrically coupled in series with the batteries to limit the current drawn from the batteries. 21. The motorized window treatment of claim 15, wherein the batteries comprise D-cell batteries and the batteries have a lifetime of approximately three years. 22. The motorized window treatment of claim 15, wherein the batteries are the sole source of power for the motor drive unit. 23. The motorized window treatment of claim 15, wherein the batteries are hidden when the battery packs are installed in the motorized window treatment. 24. The motorized window treatment of claim 1, further comprising: a headrail for housing the motor drive unit;wherein the drive assembly comprises a drive shaft located in the headrail and mechanically coupled to the motor, the drive assembly further comprising at least one lift cord that is rotatably received around the drive shaft and extends to a bottom of the covering material, the motor drive unit configured to rotate the drive shaft to raise and lower the covering material between the fully-open position and the fully-closed position. 25. The motorized window treatment of claim 24, further comprising: a spring assist assembly mechanically coupled to the drive shaft to provide torque on the drive shaft in a direction opposite a direction of a torque provided on the drive shaft by the lift cord. 26. The motorized window treatment of claim 1, further comprising: a headrail for housing the motor drive unit;wherein the drive assembly comprises two drive shafts extending from both sides of the motor drive unit and rotatably coupled to the motor drive unit thereby allowing rotations of the motor to result in rotations of the drive shafts, the drive assembly further comprising first and second lift cords, the first lift cord located proximate to the first opposite end of the headrail and the second lift cord located proximate to the second opposite end of the headrail, each lift cord rotatably received around a respective one of the drive shafts and extending vertically to a bottom end of the covering material. 27. The motorized window treatment of claim 26, wherein the motor drive unit further comprises a motor, a gear assembly operatively coupled to an output shaft of the motor, and two output gears located on each side of the motor drive unit, each of the output gears coupled to one of the drive shafts, the motor drive unit further comprising a coupling member coupled between the gear assembly and the output gears to enable rotations of the output shaft of the motor to result in rotations of the drive shafts. 28. The motorized window treatment of claim 1, wherein the drive assembly comprises a roller tube configured to windingly receive the covering material, the motor drive unit configured to rotate the roller tube to raise and lower the covering material between the fully-open position and the fully-closed position. 29. The motorized window treatment of claim 1, wherein the at least one battery pack comprises a plurality of batteries electrically coupled in series with a first diode, the motorized window treatment further comprising a second diode having a cathode electrically coupled to a cathode of the first diode, the series-coupled batteries configured to generate a battery voltage at the junction of the cathodes of the first and second diodes, the second diode having an anode adapted to receive a supply voltage from an external DC power supply. 30. A motorized window treatment comprising: a covering material;a drive assembly configured to raise and lower the covering material;a motor drive unit including a motor configured to drive the drive assembly to raise and lower the covering material between a fully-open position and a fully-closed position and to any position intermediate the fully-open and fully-closed positions; andat least one battery pack configured to hold at least one battery for producing a battery voltage to power the motor drive unit;wherein the motor drive unit is configured to determine that the magnitude of the battery voltage is too low for continued operation and reserve enough energy in the battery to allow for at least one additional movement of the covering material to the fully-open position. 31. The motorized window treatment of claim 30, wherein the motor drive unit comprises a motor and a controller configured to rotate the motor to adjust the position of the covering material, the controller configured to monitor the magnitude of the battery voltage and operate the motor at a reduced motor speed in response to the state of charge being reduced below a predetermined threshold. 32. A motorized window treatment comprising: a covering material;a drive assembly configured to raise and lower the covering material;a motor drive unit including a motor configured to drive the drive assembly to raise and lower the covering material between a fully-open position and a fully-closed position and to any position intermediate the fully-open and fully-closed positions; andat least one battery pack configured to hold at least one battery for producing a battery voltage to power the motor drive unit;wherein the motor drive unit comprises a motor and a controller configured to drive the motor to adjust the position of the covering material, the motor drive unit further comprising a power supply configured to receive the battery voltage and generate a DC supply voltage having a first nominal magnitude for powering the controller, the controller configured to increase the magnitude of the DC supply voltage to a second increased magnitude greater than the first magnitude when the controller is driving the motor to raise and lower the covering material. 33. A motorized window treatment comprising: a covering material;a drive assembly configured to raise and lower the covering material;a motor drive unit including a motor configured to drive the drive assembly to raise and lower the covering material between a fully-open position and a fully-closed position and to any position intermediate the fully-open and fully-closed positions, the motor drive unit comprising a controller and a rotational position sensor to enable the motor drive unit to sense movement of an output shaft of the motor, the controller configured to determine the position of a bottom end of the covering material in response to the rotational position sensor, the motor drive unit having a memory configured to store position data related to the determined position; andat least one battery pack configured to hold at least one battery for producing a battery voltage to power the motor drive unit; anda supplemental power source for the controller, the supplemental power source configured to maintain a charged voltage for a period of time adequate to maintain the position data when the at least one battery is removed from the battery pack;whereby the the position data is not lost when the at least one battery is removed from the battery pack. 34. The motorized window treatment of claim 33, wherein the supplemental power source comprises a capacitor electrically coupled to the battery pack for maintaining a charged voltage for a period of time adequate to maintain the position data for a time period between when the battery is removed from the battery pack and replaced in the battery pack. 35. The motorized window treatment of claim 33, wherein the supplemental power source comprises an additional battery electrically coupled to the controller to maintain power to the controller when the battery is removed from the battery pack. 36. A motorized window treatment comprising: a covering material;a drive assembly configured to raise and lower the covering material;a motor drive unit including a motor configured to drive the drive assembly to raise and lower the covering material between a fully-open position and a fully-closed position and to any position intermediate the fully-open and fully-closed positions, the motor drive unit comprising a controller and a rotational position sensor to enable the motor drive unit to sense movement of an output shaft of the motor, the controller configured to determine the position of a bottom end of the covering material in response to the rotational position sensor; andwherein the covering material is engageable by a user to manually position the covering material at any position between the fully-open position and the fully-closed positions, the rotational position sensor configured to provide at least one sensor signal to the controller so that the controller can determine the position of the covering material in response to the covering material being manually adjusted. 37. The motorized window treatment of claim 36, wherein the controller further comprises a microprocessor having a sleep mode, the microprocessor configured to use reduced electrical power during the sleep mode to conserve battery power, the motor configured to produce an electromotive force in response to the covering material being manually adjusted, the electromotive force being coupled to an input of the controller, the electromotive force at the input causing the controller to change from the sleep mode to an active mode and allow the controller to receive and process the at least one sensor signal received from the rotational position sensor, the controller determining from the sensor signal the position of the bottom end of the covering material in response to the covering material being manually adjusted.