Automatic backlight for handheld devices

• US 6,664,744 B2
• Filed: 04/03/2002
• Issued: 12/16/2003
• Est. Priority Date: 04/03/2002
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Research Laboratories (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Electric Research Laboratories, Inc. (Mitsubishi Electric Corporation)
• Inventors: Dietz, Paul H.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Tran, Chuc
• Application Number:
  US10/115,299
• Publication Number:
  US 20030189211A1
• Time in Patent Office: 622 Days
• Field of Search: 315/292, 315/291, 315/294, 315/312, 315/316, 374/163, 374/142, 356/402, 345/102
• US Class Current: 315/291
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/14 Semiconductor devices, e.g. diodes
• CPC Class Codes: G09G 3/32 semiconductive, e.g. using light-emitting diodes [LED]
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H01H 2219/038 ambient light dependent
• CPC Class Codes: H04M 1/22 Illumination; Arrangements for improving the visibility of characters on dials
• CPC Class Codes: H04W 52/027 by controlling a display operation or backlight unit
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

An automatic backlight turns on before a user hits a key, but only in dark lighting conditions. A capacitive proximity sensor detects active handling of the device and the backlight itself is used as a light sensor. The circuit requires only a single additional capacitor and three free I/O pins to implement on typical microprocessor-based systems (such as remote controls). Because the system uses the current backlight LED as a sensor, devices can often be upgraded to include this feature without changing the existing packaging.

Claims

1. An automatic backlight, comprising:

an LED coupled in series with a resistor;

a micro-processor having a first I/O pin connected to the LED and a second I/O pin coupled to the resistor;

means for periodically driving the LED in forward bias to emit light;

means for periodically driving the LED in reverse bias;

means for discharging the LED after driving the LED in reverse bias to measure a level of ambient light; and

means for adjusting a level of the emitted light according to a level of measured ambient light.

2. The automatic backlight of claim 1 wherein the level of emitted light is on or off.

3. The automatic backlight of claim 1 further comprising:

means for measuring a capacitive coupling with a user, and only driving the LED when there is a capacitive coupling with the user.

4. The automatic backlight of claim 1 further comprising:

means for measuring a capacitive coupling with a user.

5. The automatic backlight of claim 4 wherein the LED is driven only when the capacitive coupling with the user exceeds a predetermined threshold.

6. The automatic backlight of claim 4 wherein a standby signal is transmitted to a controlled device when the capacitive coupling with the user exceeds a threshold.

7. A method for operating an automatic backlight, comprising:

coupling an LED in series with a resistor;

connecting a first I/O pin of a microprocessor to the LED and a second I/O pin to the resistor;

periodically driving the LED in forward bias to emit light;

periodically driving the LED in reverse bias;

discharging the LED after driving the LED in reverse bias to measure a level of ambient light; and

adjusting a level of the emitted light according to a level of measured ambient light.