Method and system for variable LED output in an electronic device

• US 7,615,938 B2
• Filed: 04/06/2005
• Issued: 11/10/2009
• Est. Priority Date: 04/06/2005
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Prouse, Craig
• Primary Examiner(s): Vy; Hung T
• Application Number:
  US11/101,025
• Publication Number:
  US 20060226790A1
• Time in Patent Office: 1,679 Days
• Field of Search: 315/246, 315/291, 250/458.01, 345/45, 345/102, 257/88
• US Class Current: 315/291
• CPC Class Codes: H05B 45/12 using optical feedback

Abstract

A waveform generator generates LED signal values that define an LED waveform and period. Each signal value is scaled by a particular scaling value to scale the amplitude of the LED waveform. The scaled LED waveform is then transmitted to an LED to cause the light emitted by the LED to pulse at a variable brightness.

Claims

1. A system in an electronic device for emitting light from a light-emitting diode (LED) at a variable brightness, comprising:

a waveform generator for generating an LED signal waveform comprised of a plurality of LED signal values; and

a processing unit for determining a scaling value for one or more LED signal values in the plurality of LED signal values, wherein the scaling value scales the one or more LED signal values based upon a percentage of a particular LED brightness.

2. The system of claim 1, wherein the processing unit comprises a state machine unit operable to receive a time of day and determine a percentage of a particular LED brightness based on the time of day.

3. The system of claim 2, wherein the processing unit further comprises a scaling unit operable to receive the percentage of a particular LED brightness based on the time of day and determine a scaling value for each of the plurality of LED signal values using the percentage of a particular LED brightness.

4. The system of claim 3, wherein the processing unit further comprises a multiplier operable to multiply the plurality of LED signal values by respective scaling values.

5. The system of claim 1, wherein the processing unit comprising an ambient light sensor operable to sense an amount of light and generate a signal representing the amount of light.

6. The system of claim 5, wherein the processing unit further comprises a scaling unit operable to receive the signal representing the amount of light and operable to determine a scaling value for one or more LED signal values in the plurality of LED signal values.

7. The system of claim 6, wherein the processing unit further comprises a multiplier operable to multiply one or more LED signal values in the plurality of LED signal values by respective scaling values.

8. The system of claim 1, further comprising a slew rate filter operable to receive the scaled LED signal values and operable to analyze each scaled LED signal value with a previous scaled LED signal value.

9. A method for varying a brightness of light emitted from a light-emitting diode (LED) in an electronic device, comprising:

a) generating an LED signal waveform comprised of a plurality of LED signal values;

b) determining a scaling value for one or more LED signal values in the plurality of LED signal values, wherein the scaling value is based upon a percentage of a particular LED brightness; and

c) generating one or more scaled LED signal values by scaling the one or more LED signal values with the scaling value.

10. The method of claim 9, further comprising:

d) transmitting the one or more scaled LED signal values to a light emitting diode.

11. The method of claim 9, further comprising repeating a) through d) for all of the LED signal values in the plurality of LED signal values.

12. The method of claim 9, wherein determining a scaling value for one or more LED signal values in the plurality of LED signal values comprises:

receiving a clock signal representing a time of day; and

determining the percentage of a particular LED brightness, wherein the percentage comprises one or more initial brightness percentages based on the clock signal.

13. The method of claim 12, wherein determining a scaling value for one or more LED signal values in the plurality of LED signal values comprises calculating a scaling value for one or more LED signal values in the plurality of LED signal values using the one or more initial brightness percentages.

14. The method of claim 13, wherein calculating a scaling value for one or more LED signal values in the plurality of LED signal values using the one or more initial brightness percentages comprises calculating each scaling value using the equation [P/(1+k(1−

P))], where P is the initial brightness percentage and k an environmental constant.

15. The method of claim 12, wherein calculating a scaling value for one or more LED signal values in the plurality of LED signal values using the one or more initial brightness percentages comprises calculating a scaling value for one or more LED signal values based on a human perception of brightness and using the one or more initial brightness percentages.

16. The method of claim 9, wherein generating one or more scaled LED signal values by scaling the one or more LED signal values with the scaling value comprises multiplying the one or more scaling values with one or more respective LED signal values for the light-emitting diode.

17. The method of claim 9, wherein determining a scaling value for one or more LED signal values in the plurality of LED signal values comprises:

measuring an amount of light in an area;

generating a signal representative of the amount of measured light; and

determining the particular LED brightness.

18. The method of claim 17, wherein determining a scaling value for one or more LED signal values in the plurality of LED signal values comprises calculating a scaling value for one or more LED signal values in the plurality of LED signal values using the signal representative of the amount of measured light.

19. The method of claim 9, further comprising:

calculating a difference between each scaled LED signal value and a previous scaled LED signal value; and

determining whether each difference exceeds a threshold value.