Automatic backlight for handheld devices
AssigneeMitsubishi Electric Research Laboratories, Inc.
InventorPaul H. Dietz
Life of this patent
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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.
Claims7
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.
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.
Dependencies are inferred from the claim text.