Automatic backlight for handheld devices
First Claim
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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.
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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.
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Citations
7 Claims
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1. An automatic backlight, comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6)
means for measuring a capacitive coupling with a user, and only driving the LED when there is a capacitive coupling with the user.
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4. The automatic backlight of claim 1 further comprising:
means for measuring a capacitive coupling with a user.
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5. The automatic backlight of claim 4 wherein the LED is driven only when the capacitive coupling with the user exceeds a predetermined threshold.
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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.
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7. A method for operating an automatic backlight, comprising:
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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.
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Specification